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COVID-19 testing

January 01, 1970

COVID-19 testing involves analyzing samples to assess the current or past presence of SARS-CoV-2. The two main types of tests detect either the presence of the virus or antibodies produced in response to infection.[1][2] Molecular tests for viral presence through its molecular components are used to diagnose individual cases and to allow public health authorities to trace and contain outbreaks. Antibody tests (serology immunoassays) instead show whether someone once had the disease.[3] They are less useful for diagnosing current infections because antibodies may not develop for weeks after infection.[4] It is used to assess disease prevalence, which aids the estimation of the infection fatality rate.[5]

The US CDC's COVID-19 laboratory test kit

Individual jurisdictions have adopted varied testing protocols, including whom to test, how often to test, analysis protocols, sample collection and the uses of test results.[6][7][8] This variation has likely significantly impacted reported statistics, including case and test numbers, case fatality rates and case demographics.[9][10][11][12] Because SARS-CoV-2 transmission occurs days after exposure (and before onset of symptoms), there is an urgent need for frequent surveillance and rapid availability of results.[13]

Test analysis is often performed in automated, high-throughput, medical laboratories by medical laboratory scientists. Rapid self-tests and point-of-care testing are also available and can offer a faster and less expensive method to test for the virus although with a lower accuracy.[14][15]

Methods

 
Explanation of the underlying pathophysiology pertaining to diagnosis of COVID-19[16]

Positive viral tests indicate a current infection, while positive antibody tests indicate a prior infection.[17] Other techniques include a CT scan, checking for elevated body temperature, checking for low blood oxygen level, and detection by trained dogs.[18][19][20]

Detection of the virus

Detection of the virus is usually done either by looking for the virus's inner RNA, or pieces of protein on the outside of the virus. Tests that look for the viral antigens (parts of the virus) are called antigen tests.

There are multiple types of tests that look for the virus by detecting the presence of the virus's RNA. These are called nucleic acid or molecular tests, after molecular biology. As of 2021, the most common form of molecular test is the reverse transcription polymerase chain reaction (RT-PCR) test.[21] Other methods used in molecular tests include CRISPR, isothermal nucleic acid amplification, digital polymerase chain reaction, microarray analysis, and next-generation sequencing.[21]

Reverse transcription polymerase chain reaction (RT-PCR) test

Polymerase chain reaction (PCR) is a process that amplifies (replicates) a small, well-defined segment of DNA many hundreds of thousands of times, creating enough of it for analysis. Test samples are treated with certain chemicals[22][23] that allow DNA to be extracted. Reverse transcription converts RNA into DNA.

Reverse transcription polymerase chain reaction (RT-PCR) first uses reverse transcription to obtain DNA, followed by PCR to amplify that DNA, creating enough to be analyzed.[23] RT-PCR can thereby detect SARS-CoV-2, which contains only RNA. The RT-PCR process generally requires a few hours.[24] These tests are also referred to as molecular or genetic assays.[3]

Real-time PCR (qPCR)[25] provides advantages including automation, higher-throughput and more reliable instrumentation. It has become the preferred method.[26][27]

The combined technique has been described as real-time RT-PCR[28] or quantitative RT-PCR[29] and is sometimes abbreviated qRT-PCR,[30] rRT-PCR[31] or RT-qPCR,[32] although sometimes RT-PCR or PCR are used. The Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines propose the term RT-qPCR,[25] but not all authors adhere to this.

Average sensitivity for rapid molecular tests depend on the brand. For ID NOW, the average sensitivity was 73.0% with an average specificity of 99.7%; for Xpert Xpress the average sensitivity was 100% with an average specificity of 97.2%.[33][34]

In a diagnostic test, sensitivity is a measure of how well a test can identify true positives and specificity is a measure of how well a test can identify true negatives. For all testing, both diagnostic and screening, there is usually a trade-off between sensitivity and specificity, such that higher sensitivities will mean lower specificities and vice versa.

 
Sensitivity and Specificity

A 90% specific test will correctly identify 90% of those who are uninfected, leaving 10% with a false positive result.

Samples can be obtained by various methods, including a nasopharyngeal swab, sputum (coughed up material),[35] throat swabs,[36] deep airway material collected via suction catheter[36] or saliva.[37][38] Drosten et al. remarked that for 2003 SARS, "from a diagnostic point of view, it is important to note that nasal and throat swabs seem less suitable for diagnosis, since these materials contain considerably less viral RNA than sputum, and the virus may escape detection if only these materials are tested."[39]

Sensitivity of clinical samples by RT-PCR is 63% for nasal swab, 32% for pharyngeal swab, 48% for feces, 72–75% for sputum, and 93–95% for bronchoalveolar lavage.[40]

The likelihood of detecting the virus depends on collection method and how much time has passed since infection. According to Drosten tests performed with throat swabs are reliable only in the first week. Thereafter the virus may abandon the throat and multiply in the lungs. In the second week, sputum or deep airways collection is preferred.[36]

Collecting saliva may be as effective as nasal and throat swabs,[37] although this is not certain.[41][38] Sampling saliva may reduce the risk for health care professionals by eliminating close physical interaction.[42] It is also more comfortable for the patient.[43] Quarantined people can collect their own samples.[42] A saliva test's diagnostic value depends on sample site (deep throat, oral cavity, or salivary glands).[38] Some studies have found that saliva yielded greater sensitivity and consistency when compared with swab samples.[44][45][46]

On 15 August 2020, the US FDA granted an emergency use authorization for a saliva test developed at Yale University that gives results in hours.[47][48]

On 4 January 2021, the US FDA issued an alert about the risk of false results, particularly false negative results, with the Curative SARS-Cov-2 Assay real-time RT-PCR test.[49]

Viral burden measured in upper respiratory specimens declines after symptom onset.[50] Following recovery, many patients no longer have detectable viral RNA in upper respiratory specimens. Among those who do, RNA concentrations three days following recovery are generally below the range in which replication-competent virus has been reliably isolated.[51] No clear correlation has been described between length of illness and duration of post-recovery shedding of viral RNA in upper respiratory specimens.[52]

Other molecular tests

Isothermal nucleic acid amplification tests also amplify the virus's genome. They are faster than PCR because they do not involve repeated heating and cooling cycles. These tests typically detect DNA using fluorescent tags, which are read out with specialized machines.[citation needed]

CRISPR gene editing technology was modified to perform the detection: if the CRISPR enzyme attaches to the sequence, it colors a paper strip. The researchers expect the resulting test to be cheap and easy to use in point-of-care settings.[53][54] The test amplifies RNA directly, without the RNA-to-DNA conversion step of RT-PCR.[55]

Antigen tests

 
COVID-19 Antigen Rapid Test Kit; the timer is provided by the user.
 
Mucus from nose or throat in a test liquid is placed onto a COVID-19 rapid antigen diagnostic test device.
 
COVID-19 rapid testing in Rwanda

An antigen is the part of a pathogen that elicits an immune response. Antigen tests look for antigen proteins from the viral surface. In the case of a coronavirus, these are usually proteins from the surface spikes.[56] SARS-CoV-2 antigens can be detected before onset of COVID-19 symptoms (as soon as SARS-CoV-2 virus particles) with more rapid test results, but with less sensitivity than PCR tests for the virus.[57]

COVID-19 rapid antigen tests are lateral flow immunoassays that detect the presence of a specific viral antigen, which indicates current viral infection. Antigen tests produce results quickly (within approximately 15–30 minutes), and most can be used at the point-of-care or as self-tests. Self-tests are rapid tests that can be taken at home or anywhere, are easy to use, and produce rapid results.[58] Antigen tests can be performed on nasopharyngeal, nasal swab, or saliva specimens.[15]

Antigen tests that can identify SARS-CoV-2 offer a faster and less expensive method to test for the virus.[14] Antigen tests are generally less sensitive than real-time reverse transcription polymerase chain reaction (RT-PCR) and other nucleic acid amplification tests (NAATs).[15]

Antigen tests may be one way to scale up testing to much greater levels.[56] Isothermal nucleic acid amplification tests can process only one sample at a time per machine. RT-PCR tests are accurate but require too much time, energy and trained personnel to run the tests.[56] "There will never be the ability on a [PCR] test to do 300 million tests a day or to test everybody before they go to work or to school," Deborah Birx, head of the White House Coronavirus Task Force, said on 17 April 2020. "But there might be with the antigen test."[59]

Samples may be collected via nasopharyngeal swab, a swab of the anterior nares, or from saliva (obtained by various methods including lollipop tests for children).[60] The sample is then exposed to paper strips containing artificial antibodies designed to bind to coronavirus antigens. Antigens bind to the strips and give a visual readout. The process takes less than 30 minutes, can deliver results at point of care, and does not require expensive equipment or extensive training.[56]

Swabs of respiratory viruses often lack enough antigen material to be detectable.[61] This is especially true for asymptomatic patients who have little if any nasal discharge. Viral proteins are not amplified in an antigen test.[56][62] A Cochrane review based on 64 studies investigating the efficacy of 16 different antigen tests determined that they correctly identified COVID-19 infection in an average of 72% of people with symptoms, compared to 58% of people without symptoms.[63][needs update] Tests were most accurate (78%) when used in the first week after symptoms first developed, likely because people have the most virus in their system in the first days after they are infected.[63] While some scientists doubt whether an antigen test can be useful against COVID-19,[62] others have argued that antigen tests are highly sensitive when viral load is high and people are contagious, making them suitable for public health screening.[64][65] Routine antigen tests can quickly identify when asymptomatic people are contagious, while follow-up PCR can be used if confirmatory diagnosis is needed.[66]

Antibody tests

 
 
Left: Automated analyzer for immunoassays, used, for example, to find SARS-CoV-2 antibodies. Right: Example of quantitative results for SARS-CoV-2 antibody test.

The body responds to a viral infection by producing antibodies that help neutralize the virus.[67] Blood tests (also called serology tests or serology immunoassays[3]) can detect the presence of such antibodies.[68] Antibody tests can be used to assess what fraction of a population has once been infected, which can then be used to calculate the disease's mortality rate.[5] They can also be used to determine how much antibody is contained in a unit of convalescent plasma, for COVID-19 treatment, or to verify if a given vaccine generates an adequate immune response.[69]

SARS-CoV-2 antibodies' potency and protective period have not been established.[5][70] Therefore, a positive antibody test may not imply immunity to a future infection. Further, whether mild or asymptomatic infections produce sufficient antibodies for a test to detect has not been established.[71] Antibodies for some diseases persist in the bloodstream for many years, while others fade away.[56]

The most notable antibodies are IgM and IgG. IgM antibodies are generally detectable several days after initial infection, although levels over the course of infection and beyond are not well characterized.[72] IgG antibodies generally become detectable 10–14 days after infection and normally peak around 28 days after infection.[73][74] This pattern of antibody development seen with other infections, often does not apply to SARS-CoV-2, however, with IgM sometimes occurring after IgG, together with IgG or not occurring at all.[75] Generally, however, median IgM detection occurs 5 days after symptom onset, whereas IgG is detected a median 14 days after symptom onset.[76] IgG levels significantly decline after two or three months.[77]

Genetic tests verify infection earlier than antibody tests. Only 30% of those with a positive genetic test produced a positive antibody test on day 7 of their infection.[71]

Antibody Test Types

Rapid diagnostic test (RDT)

RDTs typically use a small, portable, positive/negative lateral flow assay that can be executed at point of care. RDTs may process blood samples, saliva samples, or nasal swab fluids. RDTs produce colored lines to indicate positive or negative results.[78]

Enzyme-linked immunosorbent assay (ELISA)

ELISAs can be qualitative or quantitative and generally require a lab. These tests usually use whole blood, plasma, or serum samples. A plate is coated with a viral protein, such as a SARS-CoV-2 spike protein. Samples are incubated with the protein, allowing any antibodies to bind to it. The antibody-protein complex can then be detected with another wash of antibodies that produce a color/fluorescent readout.[78]

Neutralization assay

Neutralization assays assess whether sample antibodies prevent viral infection in test cells.[67] These tests sample blood, plasma or serum. The test cultures cells that allow viral reproduction (e.g., Vero E6 cells). By varying antibody concentrations, researchers can visualize and quantify how many test antibodies block virus replication.[78]

Chemiluminescent immunoassay

Chemiluminescent immunoassays are quantitative lab tests. They sample blood, plasma, or serum. Samples are mixed with a known viral protein, buffer reagents and specific, enzyme-labeled antibodies. The result is luminescent. A chemiluminescent microparticle immunoassay uses magnetic, protein-coated microparticles. Antibodies react to the viral protein, forming a complex. Secondary enzyme-labeled antibodies are added and bind to these complexes. The resulting chemical reaction produces light. The radiance is used to calculate the number of antibodies. This test can identify multiple types of antibodies, including IgG, IgM, and IgA.[78]

Neutralizing vis-à-vis binding antibodies

Most if not all large scale COVID-19 antibody testing looks for binding antibodies only and does not measure the more important neutralizing antibodies (NAb).[79][80][81] A NAb is an antibody that neutralizes the infectivity of a virus particle by blocking its attachment to or entry into a susceptible cell; enveloped viruses, like e.g. SARS-CoV-2, are neutralized by the blocking of steps in the replicative cycle up to and including membrane fusion.[82][67] A non-neutralizing antibody either does not bind to the crucial structures on the virus surface or binds but leaves the virus particle infectious; the antibody may still contribute to the destruction of virus particles or infected cells by the immune system.[83][67] It may even enhance infectivity by interacting with receptors on macrophages.[84] Since most COVID-19 antibody tests return a positive result if they find only binding antibodies, these tests cannot indicate that the subject has generated protective NAbs that protect against re-infection.[80][81]

It is expected that binding antibodies imply the presence of NAbs[81] and for many viral diseases total antibody responses correlate somewhat with NAb responses[85] but this is not established for COVID-19. A study of 175 recovered patients in China who experienced mild symptoms reported that 10 individuals had no detectable NAbs at discharge, or thereafter. How these patients recovered without the help of NAbs and whether they were at risk of re-infection was not addressed.[80] An additional source of uncertainty is that even if NAbs are present, viruses such as HIV can evade NAb responses.[79]

Studies have indicated that NAbs to the original SARS virus (the predecessor to the current SARS-CoV-2) can remain active for two years[86] and are gone after six years.[87] Nevertheless, memory cells including memory B cells and memory T cells[88] can last much longer and may have the ability to reduce reinfection severity.[87]

  •  
    A point of care test in Peru. A blood droplet is collected by a pipette.
  •  
    Blood from pipette is then placed onto a COVID-19 rapid diagnostic test device.
  •  
    The rapid diagnostic test shows reactions of IgG and IgM antibodies. The left tray shows a negative result, and the right positive
  •  
    Home test with a positive result. The "C" is the control; the "T" is the test

Other tests

Sniff tests

Sudden loss of smell can be used to screen people on a daily basis for COVID-19. A study by the National Institutes of Health showed that those infected with SARS-CoV-2 could not smell a 25% mixture of ethanol and water.[89] Because various conditions can lead to the loss of the sense of smell, a sniff test would not be definitive but indicate the need for a PCR test. Because the loss of the sense of smell shows up before other symptoms, there has been a call for widespread sniff testing.[90] Health care bureaucracies have generally ignored sniff tests even though they are quick, easy and capable of being self-administered daily. This has led some medical journals to write editorials supporting the adoption of sniff testing.[91]

Imaging

Typical visible features on CT initially include bilateral multilobar ground-glass opacities with a peripheral or posterior distribution.[92] COVID-19 can be identified with higher precision using CT than with RT-PCR.[93]

Subpleural dominance, crazy paving, and consolidation may develop as the disease evolves.[92][94] Chest CT scans and chest x-rays are not recommended for diagnosing COVID-19. Radiologic findings in COVID-19 lack specificity.[92][95]

Chest X-rays, computed tomography scans and ultrasounds are all ways the coronavirus disease can be detected.

A chest x-ray is a portable lightweight machine. This machine is typically more available than polymerase chain reaction and computerized tomography scans. it only takes approximately 15 seconds per patient.[96] This makes chest-x ray readily accessible and inexpensive. It also has quick turnaround time and can be crucial to the clinical equipment in the detection of coronavirus disease.[97] Computerized tomography scans involve looking at 3D images from various angles. This is not as available as chest x-ray, but still only takes about 15 minutes per patient.[96] Computerized tomography has been a known routine scanning for pneumonia diagnosis, therefore can also be used to diagnose coronavirus disease. Computerized tomography scans may help with ongoing illness monitoring throughout treatment. Patients who had low-grade symptoms and high body temperatures revealed significant lung indications on their chest computed tomography scans. They emphasized how important chest computerized tomography scans are for determining how serious the coronavirus disease infection is.[98]

Ultrasound can be another tool to detect coronavirus disease. An ultrasound is a type of imaging exam that produces images using sound waves. Unlike computerized tomography scans and x-rays, ultrasound does not use radiation. Moreover, it is inexpensive, simple to use, repeatable, and has several additional advantages. Using a hand-held mobile machine, ultrasound examinations can be performed in a variety of healthcare settings.[99]

There are some downsides to using imaging, however. The equipment needed for computed tomography scans is not available in most hospitals, making it not as effective as some other tools used for detection of the coronavirus disease.[96] One of the difficult tasks in a pandemic is manually inspecting each report, which takes numerous radiology professionals and time.[100] There were several problems with early studies of using chest computerized tomography scans for diagnosing coronavirus. Some of these problems included the disease severity characters being different in severe and hospitalized cases. The criteria for doing a chest computerized tomography scan were not defined. There was also no characterization of positive chest computerized tomography scans results. The computerized tomography scans findings were not the same as positive computerized tomography scans findings of coronavirus.[99] In a typical clinical setting, chest imaging is not advised for routine screening of COVID-19. Patients with asymptomatic to mild symptoms are not recommended to be tested via chest computerized tomography scans. However, it is still crucial to use, particularly when determining complications or disease progression. Chest imaging also is not always the first route to take with patients who have high risk factors for COVID. High risk patients that had mild symptoms, chest imaging findings were limited. Although a computerized tomography scan is a strong tool in the diagnosis of COVID-19, it is insufficient to identify COVID-19 alone due to the poor specificity and the difficulties that radiologists may experience in distinguishing COVID-19 from other viral pneumonia on chest computerized tomography scans.[98]

Serology (CoLab score) tests

The standard blood test (quick scan) taken at the emergency room measures different values. By use of the blood quick scan the CoLab score is calculated with a developed algorithm based on how the coronavirus causes changes in the blood. The software is intended for use in emergency rooms to quickly rule out the presence of the disease in incoming patients. A not negative result is followed by a PCR (polymerase chain reaction) or LAMP (loop-mediated isothermal amplification) test.[101]

Breath tests

The breath test by a Coronavirus breathalyzer is a pre-screening test for people who have no or mild symptoms of COVID-19. A not negative result is followed by a PCR or LAMP test.[citation needed]

Animals

In May 2021, Reuters reported that Dutch researchers at Wageningen University had shown that trained bees could detect the virus in infected samples in seconds and this could benefit countries where test facilities are in short supply.[102] A two-month study by the Necker-Cochin hospital Paris in conjunction with the French national veterinary school reported in May 2021 that dogs were more reliable than current lateral flow tests.[103]

Researchers in Paris in March 2022 reported in a preprint not yet peer-reviewed that trained dogs were very effective for rapidly detecting the presence of SARS-Cov2 in people, whether displaying symptoms or not. The dogs were presented with sweat samples to smell from 335 people, of whom 78 with symptoms and 31 without tested positive by PCR. The dogs detected 97% of the symptomatic and 100% of the asymptomatic infections. They were 91% accurate at identifying volunteers who were not infected, and 94% accurate at ruling out the infection in people without symptoms. The authors said "Canine testing is non-invasive and provides immediate and reliable results.Further studies will be focused on direct sniffing by dogs to evaluate sniffer dogs for mass pre-test in airports, harbors, railways stations, cultural activities or sporting events."[104][105]

Functional assays

Tollotest is a molecular test that detects the activity of a SARS-CoV2 protease, which is a biomarker for active infection.[106]

History

Main article: Development of COVID-19 tests
 
Timeline of total number of tests in different countries[107]

In January 2020, scientists from China published the first genetic sequences of SARS-CoV-2 via virological.org,[108] a "hub for prepublication data designed to assist with public health activities and research".[109] Researchers around the world used that data to build molecular tests for the virus. Antigen- and antibody-based tests were developed later.[citation needed]

Even once the first tests were created, the supply was limited. As a result, no countries had reliable data on the prevalence of the virus early in the pandemic.[110] The WHO and other experts called for ramping up testing as the best way to slow the spread of the virus.[111][112] Shortages of reagent and other testing supplies became a bottleneck for mass testing in the EU, the UK and the US.[113][114][115] Early tests also encountered problems with reliability.[116][117]

Testing protocols

Drive-through testing

In drive-through testing, the person undergoing testing remains in a vehicle while a healthcare professional approaches the vehicle and obtains a sample, all while taking appropriate precautions such as wearing personal protective equipment (PPE).[118][119] Drive-through centers helped South Korea accelerate its testing program.[120]

Home collection

 
A Randox PCR home test kit in the UK, showing the swab, and multi-layer packaging to deliver it to the lab
 
A USPS package containing COVID-19 tests from the fifth round of free US distributions in the fall of 2023, with instructions regarding FDA extensions of test expiration dates.

In Hong Kong test subjects can stay home and receive a specimen tube. They spit into it, return it and later get the result.[121] Additionally, by the fall of 2023, the United States had conducted six rounds of mailing free at-home COVID-19 tests to households nationwide. The rapid antigen tests, while less accurate than PCR tests, did not require mailing the tests back to labs for analysis.[122][123]

Pooled testing

See also: List of countries implementing pool testing strategy against COVID-19

Pooled testing can improve turnaround time, by combining a number of samples to be tested together. If the pool result is negative, all samples are negative. If the test result is positive, samples will need to be individually tested.[69]

In Israel, researchers at Technion and Rambam Hospital developed a method for testing samples from 64 patients simultaneously, by pooling the samples and only testing further if the combined sample was positive.[124][125][126] Pool testing was then adopted in Israel, Germany, Ghana[127][128][129] South Korea,[130] Nebraska,[131] China[132] and the Indian states of Uttar Pradesh,[133] West Bengal,[134] Punjab,[135] Chhattisgarh[136] and Maharashtra.[137]

Open source, multiplexed designs released by Origami Assays can test as many as 1122 patient samples using only 93 assays.[138] These balanced designs can be run in small laboratories without robotic liquid handlers.

Multi-tiered testing

One study proposed a rapid immune response assay as a screening test, with a confirmatory nucleic acid test for diagnosis, followed by a rapid antibody test to determine course of action and assess population exposure/herd immunity.[139]

Required volume

Required testing levels are a function of disease spread. The more the cases, the more tests are needed to manage the outbreak. COVID-19 tends to grow exponentially at the beginning of an outbreak, meaning that the number of required tests initially also grows exponentially. If properly targeted testing grows more rapidly than cases, it can be contained.[citation needed]

WHO recommends increasing testing until fewer than 10% are positive in any given jurisdiction.[140]

United States

 
Number of tests done per day in the US, as of April 2020.
Blue: CDC lab
Orange: Public health lab
Gray: Data incomplete due to reporting lag
Not shown: Testing at private labs; total exceeded 100,000 per day by 27 March.[141]

Economist Paul Romer reported that the US has the technical capacity to scale up to 20 million tests per day, which is his estimate of the scale needed to fully remobilize the economy.[142] The Edmond J. Safra Center for Ethics estimated on 4 April 2020 that this capacity could be available by late July 2020.[143] Romer pointed to single-molecule real-time sequencing equipment from Pacific Biosciences[142][144] and to the Ion Torrent Next-Generation Sequencing equipment from ThermoFisher Scientific.[142][145] According to Romer, "Recent research papers suggest that any one of these has the potential to scale up to millions of tests per day." This plan requires removing regulatory hurdles. Romer estimated that $100 billion would cover the costs.[142]

Romer also claimed that high test accuracy is not required if tests are administered frequently enough. He ran model simulations in which 7% of the population is tested every day using a test with a 20% false negative rate and a 1% false positive rate. The average person would be tested roughly every two weeks. Those who tested positive would go into quarantine. Romer's simulation indicated that the fraction of the population that is infected at any given time (known as the attack rate) peaks reaches roughly 8% in about thirty days before gradually declining, in most runs reaching zero at 500 days, with cumulative prevalence remaining below 20%.[146]

Snapshot mass-testing

A study found that, despite possibly suboptimal implementation, the snapshot mass-testing approach conducted by Slovakia by which ~80% of its population was tested for COVID-19 within a weekend at the end of October 2020 was thought highly efficacious, decreasing observed prevalence by 58% within one week and by 70% compared to a hypothetical scenario of no snapshot mass-testing. [147][148] The significant reduction resulted from a set of complementary lockdown and quarantine measures whereby citizens who tested positive were quarantined synchronously the weeks afterwards.[149] The country increased other countermeasures at the same time so the inference was questionable. In the following months Slovakia's COVID-19 death rate per population increased to among the highest in the world. Research on mass testing suggests that people who test negative think it is safe to travel and come in contact with infected people. In the U.S. the tracing system was overwhelmed. On 70 percent of days there were more cases than tracers had time to contact and people contacted were often uncooperative. [150]

Surveillance and screening of populations

See also: Pandemic prevention § Surveillance and mapping

As of August 2020, the WHO recognizes wastewater surveillance of SARS-CoV-2 as a potentially useful source of information on the prevalence and temporal trends of COVID-19 in communities, while highlighting that gaps in research such as viral shedding characteristics should be addressed.[151] Such aggregative testing may have detected early cases.[152] Studies show that wastewater-based epidemiology has the potential for an early warning system and monitoring for COVID-19 infections.[153][154][155][156][157] This may prove particularly useful once large shares of regional populations are vaccinated or recovered and do not need to conduct rapid tests while in some cases being infectious nevertheless.[158]

Available tests

 
A temporary drive-in testing site for COVID-19 set up with tents in a parking lot

Countries around the world developed tests independently and in partnership with others.

Nucleic acid tests

Tests are available that look for viral DNA using either polymerase chain reaction (PCR) or loop-mediated isothermal amplification (LAMP) technology.

Tests developed in China, France, Germany, Hong Kong, Japan, the United Kingdom, and the US targeted different parts of the viral genome. WHO adopted the German system for manufacturing kits sent to low-income countries without the resources to develop their own.[citation needed]

PowerChek Coronavirus looks for the "E" gene shared by all beta coronaviruses, and the RdRp gene specific to SARS-CoV-2.[159]

 
US President Donald Trump displays a COVID-19 testing kit from Abbott Laboratories in March 2020.
 
Nucleic acid testing conducted using an Abbott Laboratories ID Now device

Abbott Laboratories' ID Now nucleic acid test uses isothermal amplification technology.[160] The assay amplifies a unique region of the virus's RdRp gene; the resulting copies are then detected with "fluorescently-labeled molecular beacons".[161] The test kit uses the company's "toaster-size" ID Now device, which is widely deployed in the US.[162] The device can be used in laboratories or in point of care settings, and provides results in 13 minutes or less.[161]

Primerdesign offers its Genesig Real-Time PCR test system. Roche Molecular Systems offers the Cobas 6800/8800 systems; they are offered among others by the United Nations.[citation needed]

Antigen tests

Main article: COVID-19 rapid antigen test
 
Innova SARS-CoV-2 Antigen Rapid Qualitative Lateral Flow Test kit showing a negative result. This device has been subject to accuracy concerns and a recall in the United States.

Antigen tests are readily available worldwide and have been approved by several health regulators.

Quidel's "Sofia 2 SARS Antigen FIA"[66][163] is a lateral flow test that uses monoclonal antibodies to detect the virus's nucleocapsid (N) protein.[164] The result is read out by the company's Sofia 2 device using immunofluorescence.[164] The test is simpler and cheaper but less accurate than nucleic acid tests. It can be deployed in laboratories or at point of care and gives results in 15 minutes.[163] A false negative result occurs if the sample's antigen level is positive but below the test's detection limit, requiring confirmation with a nucleic acid test.[164]

The Innova SARS-CoV-2 Antigen Rapid Qualitative Test was never approved for use in the United States, but was being sold by the company anyway. The FDA inspected Innova facilities in California in March and April 2021, and found inadequate quality assurance of tests manufactured in China.[165] On 23 April 2021, the company issued a recall. The FDA warned consumers to return or destroy the devices because the rate of false positives and false negatives found in clinical trials were higher than the rate claimed by the packaging.[166] Over 1 billion tests from the company have been distributed in the UK, with £3 billion in funding as part of Operation Moonshot, and the MHRK has authorized exceptional use until at least 28 August 2021.[165] Concerned experts pointed out that accuracy dropped significantly when screening was conducted by the public instead of by a medical professional, and that the test was not designed to screen asymptomatic people.[165] A 2020 study found 79% of positive cases were found when used by laboratory scientists, but only 58% when used by the general public and 40% when used for city-wide screening in Liverpool.[167]

Serology (antibody) tests

Antibodies are usually detectable 14 days after the onset of the infection. Multiple jurisdictions survey their populations using these tests.[168][169] The test requires a blood sample.

Private US labs including Quest Diagnostics and LabCorp offer antibody testing upon request.[170]

Certain antibody tests are available in several European countries and also in the US.[171][172]

Roche offers a selective ELISA serology test.[173]

A summary review in BMJ has noted that while some "serological tests … might be cheaper and easier to implement at the point of care [than RT-PCR]", and such testing can identify previously infected individuals, "caution is warranted … using serological tests for … epidemiological surveillance". The review called for higher quality studies assessing accuracy with reference to a standard of "RT-PCR performed on at least two consecutive specimens, and, when feasible, includ[ing] viral cultures."[174][175] CEBM researchers have called for in-hospital 'case definition' to record "CT lung findings and associated blood tests"[176] and for the WHO to produce a "protocol to standardise the use and interpretation of PCR" with continuous re-calibration.[177]

Accuracy

The location of sample collection impact on sensitivity for COVID-19 in 205 Wuhan patients[178]
Samples source Positive rate
Bronchoalveolar lavage fluid specimens 93% (14/15)
Sputum 72% (75/104)
Nasal swabs 63% (5/8)
Fibrobronchoscope brush biopsy 46% (6/13)
Pharyngeal swabs 32% (126/398)
Feces 29% (44/153)
Blood 1% (3/307)

Accuracy is measured in terms of specificity and selectivity. Test errors can be false positives (the test is positive, but the virus is not present) or false negatives, (the test is negative, but the virus is present).[179] In a study of over 900,000 rapid antigen tests, false positives were found to occur at a rate of 0.05% or 1 in 2000.[180]

Sensitivity and specificity

Main article: Sensitivity and specificity

Sensitivity indicates whether the test accurately identifies whether the virus is present. Each test requires a minimum level of viral load in order to produce a positive result. A 90% sensitive test will correctly identify 90% of infections, missing the other 10% (a false negative). Even relatively high sensitivity rates can produce high rates of false negatives in populations with low incidence rates.[179]

In a diagnostic test, sensitivity is a measure of how well a test can identify true positives and specificity is a measure of how well a test can identify true negatives. For all testing, both diagnostic and screening, there is usually a trade-off between sensitivity and specificity, such that higher sensitivities will mean lower specificities and vice versa.

 
Sensitivity and Specificity

A 90% specific test will correctly identify 90% of those who are uninfected, leaving 10% with a false positive result.[citation needed]

Low-specificity tests have a low positive predictive value (PPV) when prevalence is low. For example, suppose incidence is 5%. Testing 100 people at random using a test that has a specificity of 95% would yield on average 5 people who are actually negative who would incorrectly test positive. Since 5% of the subjects actually are positive, another five would also test positive correctly, totaling 10 positive results. Thus, the PPV is 50%,[181] an outcome no different from a coin toss. In this situation, assuming that the result of a second test is independent of the first test, retesting those with a first positive result increases the PPV to 94.5%, meaning that only 4.5% of the second tests would return the incorrect result, on average less than 1 incorrect result.[182]

Causes of test error

The time course of infection affects the accuracy of some tests. Samples may be collected before the virus has had a chance to establish itself or after the body has begun to eliminate it. A May 2020 review of PCR-RT testing found that the median probability of a false-negative result decreased from 100% on day 1, to 67% on day 4. On the day of symptom onset, the probability was 38%, which decreased to 20% 3 days later.[183][needs update]

PCR-based test

 
Detection of SARS-CoV-2 by nasal swab over six weeks in patients who experienced mild to moderate illness

RT-PCR is the most commonly-used diagnostic test.[184] PCR tests by nasopharyngeal swab have a sensitivity of 73%, but systematic analysis of specificity has not been determined due to the lack of PCR studies with a control group.[185]

In one study sensitivity was highest at week one (100%), followed by 89.3%, 66.1%, 32.1%, 5.4% and zero by week six since symptom onset.[186][failed verification][187]

Sensitivity is also a function of the number of PCR cycles, as well as time and temperature between sample collection and analysis.[188] A cycle threshold of 20 cycles would be adequate to detect SARS-Cov-2 in a highly infective person.[188] Cycle thresholds above 34 are increasingly likely to give false positives outside of high biosafety level facilities.[188]

On July 16, 2020, Dr. Anthony Fauci of the US CDC indicated that positive results obtained from RT-PCR tests run at more than 35 cycles were almost always "just dead nucleotides".[189] On August 29, 2020, the New York Times reported that, "In three sets of testing data that include cycle thresholds, compiled by officials in Massachusetts, New York and Nevada … most tests set the limit at 40 [cycles], a few at 37" and that the CDC was examining the use of cycle threshold measures "for policy decisions,"[190] On July 21, 2021, the CDC, in their "Real-Time RT-PCR Diagnostic Pan: Instructions for Use", indicated tests results should be determined at 40 cycles.[191]

A Dutch CDC-led laboratory investigation compared 7 PCR kits.[192] Test kits made by BGI, R-Biopharm AG, BGI, KH Medical and Seegene showed high sensitivity.[193]

High sensitivity kits are recommended to assess people without symptoms, while lower sensitivity tests are adequate when diagnosing symptomatic patients.[192]

The University of Oxford's Centre for Evidence-Based Medicine (CEBM) has pointed to mounting evidence[194][195] that "a good proportion of 'new' mild cases and people re-testing positives via RT-PCR after quarantine or discharge from hospital are not infectious, but are simply clearing harmless virus particles which their immune system has efficiently dealt with", and have called for "an international effort to standardize and periodically calibrate testing".[176] On 7 September, the UK government issued "guidance for procedures to be implemented in laboratories to provide assurance of positive SARS-CoV-2 RNA results during periods of low prevalence, when there is a reduction in the predictive value of positive test results".[196]

On 4 January 2021, the US FDA issued an alert about the risk of false results, particularly false negative results, with the Curative SARS-Cov-2 Assay real-time RT-PCR test.[49]

Isothermal nucleic amplification test

One study reported that the ID Now COVID-19 test showed sensitivity of 85.2%. Abbott responded that the issue could have been caused by analysis delays.[197] Another study rejected the test in their clinical setting because of this low sensitivity.[198]

Confirmatory testing

The WHO recommends countries that do not have testing capacity and national laboratories with limited experience on COVID-19 send their first five positives and the first ten negative COVID-19 samples to one of the 16 WHO reference laboratories for confirmatory testing.[199][200] Out of the sixteen reference laboratories, seven are in Asia, five in Europe, two in Africa, one in North America and one in Australia.[201]

National or regional responses

Iceland

Iceland managed the pandemic with aggressive contact tracing, inbound travel restrictions, testing, and quarantining, but with less aggressive lock-downs.[202]

India

Main article: COVID-19 pandemic in India § Testing and countermeasures

Italy

Researchers tested the entire population of Vo', the site of Italy's first COVID-19 death. They tested about 3,400 people twice, at an interval of ten days. About half the people testing positive had no symptoms. All discovered cases were quarantined. Along with restricting travel to the commune, new infections were eliminated.[203]

Japan

Unlike other Asian countries, Japan did not experience a pandemic of SARS or MERS, so the country's PCR testing system was not well developed.[204][205] Japan preferentially tested patients with severe illness and their close contacts at the beginning. Japan's Novel Coronavirus Expert Meeting chose cluster measures to identify infections clusters.[204][205] The Expert Meeting analyzed the outbreak from Wuhan and identified conditions leading to clusters (closed spaces, crowded spaces and close-contact), and asked people to avoid them.[205][206]

In January, contact tracers took action shortly after the first infection was found. Only administrative tests were carried out at first, until insurance began covering PCR tests on 6 March. Private companies began to test, and the test system gradually expanded.[204][207]

On 3 April, those with positive tests were legally permitted to recuperate at home or in a hotel if they had asymptomatic or mild illness, ending the hospital bed shortage.[208] The first wave (from China) was contained,[209] but a second wave (caused by returnees from Europe and the US) in mid-March led to spreading infection in April.[205] On 7 April, Japan declared a state of emergency (less strict than a lockdown, because it did not block cities or restrict outings).[205][208][210] On 13 May, antigen test kits became covered by insurance, and were combined with a PCR test for diagnosis.[211][212]

Japan's PCR test count per capita remained far smaller than in some other countries even though its positive test rate was lower. Excess mortality was observed in March.[206][failed verification][210][failed verification][213] The Expert Meeting stated, "The Japanese health care system originally carries out pneumonia surveillance, allowing it to detect most of the severely ill patients who develop pneumonia. There are a large number of CT scanners in Japan and they have spread to small hospitals all over the country, so pneumonia patients are rarely missed. In that sense, it meets the same standards as other countries that mainly carry out PCR tests."[206][213] The group recommended using CT scans data and doctor's findings for diagnosis.[214][215] On the Diamond Princess cruise ship, many people who initially tested negative later tested positive. Half of coronavirus-positives there who remained mild or asymptomatic had pneumonia findings on CT scans and their CT image showed a frosted glass shadow that is characteristic of infection.[214][216]

As of 18 July, Japan's daily PCR testing capacity was about 32,000, more than three times the 10,000 cases as of April. When the antigen test is added to it, the number is about 58,000. The number of tests per 1,000 people in the United States is about 27 times that of Japan, the UK is 20 times, Italy is 8 times, and South Korea is twice (as of 26 July).[217][218][219] The number of those infected with coronavirus and inpatients has increased in July, but the number of serious cases has not increased. This is thought to be due to the proper testing of those infected in July compared to those in April. In April, the number of tests could not catch up with the increase in the number of infected people, and the test standards were strict, so the test positive rate exceeded 30% at the peak. It means that there were quite a few cases where those infected were not PCR tested. It is thought that the severe case was preferentially tested though there were a lot of mild cases and asymptomatic carriers mainly in the young during the first wave. In other words, it became possible to grasp the actual situation of infection much better than before by strengthening the testing system.[220] At the end of July, accommodation facilities for mild and asymptomatic carriers became full, and the authorities requested hospitals to prepare beds for the mild. However, it became difficult to treat patients with other illnesses and to maintain the ICU system including the staff due to the occupation of hospital beds by patients with mild symptoms.[221][222][223]

Russia

On 27 April 2020, Russia tested 3 million people and had 183,000 positive results.[224] On 28 April Anna Popova, head of Federal Service for Surveillance in Healthcare (Roszdravnadzor) stated that 506 laboratories were testing; that 45% of those who tested positive had no symptoms; that 5% of patients had a severe form; and 40% of infections were from family members. Illness improved from six days to one day after symptoms appeared. Antibody testing was carried out on 3,200 Moscow doctors, finding 20% immunity.[225]

Singapore

With contact tracing, inbound travel restrictions, testing, and quarantining, Singapore arrested the initial spread without complete lockdown.[226]

Slovakia

In late October 2020 Slovakia tested 3.62 million people in a weekend, from a population of 5.4m, representing 67% of the total (or 82% of the adult population), 38,359 tested positive, representing 1.06% of those tested. The government considered the mass test would significantly assist in controlling the virus and avoid a lockdown and may repeat the exercise at a later date.[227]

South Korea

South Korea's broad testing approach helped reduce spread. Testing capacity, largely in private sector labs, was built up over several years by the South Korean government in the early 2000s.[228]

The government exploited the resident registration number (RRN) system. Authorities mobilized young men who were eligible for military service as social service agents, security and public health doctors. Public health doctors were mainly dispatched to public health centers and life treatment centers where mildly ill patients were accommodated. They performed PCR tests and managed mild patients. Social service agents worked in pharmacies to fill staff shortages. Korea's 10k PCR tests per million residents was the world's highest as of 13 April rising to 20k by mid-June. Twenty-seven Korean companies exported test kits worth $48.6 million in March, and were asked to provide test kits or humanitarian assistance by more than 120 countries. Korean authorities set up a treatment center to isolate and manage patients with asymptomatic and minor illnesses in one facility in order to vacate hospital beds for the more severely ill.

Centers were sited mainly at national facilities and corporate training centers. The failure of Korea's MERS quarantine in May 2015 left Korea more prepared for COVID-19 than countries that did not face that pandemic. Then President Park Geun-hye allowed Korean CDC-approved private sector testing for infectious diseases in 2016. Korea already had a system for isolating, testing and treating infectious disease patients separately from others. Patients with respiratory illness but no epidemiological relevance were treated at the National Hospital, and those with epidemiological relevance were treated at selected clinics.[229][230][231][232][233][234][235][236][237]

Korea established a large scale drive-through/walk-through" test testing program. However, the most common method was "mobile examination". In Daegu City, 54% of samples were collected by 23 March in home or hospital. Collecting samples door-to-door of avoided the risk of travel by possibly infected patients, but required additional staff. Korea solved the problem by drafting more than 2,700 public insurance doctors.[229][233][232]

The government disclosed personal information to the public via KCDC without patient consent. The authorities used digital surveillance to trace possible spread.[230][233][234][236][237][238][239][240][241][242][excessive citations]

Taiwan

Health insurance IDs and national identification card numbers were used to trace contacts.[243][244][245][246]

United Arab Emirates

In January 2021, the COVID-19 testing results of the UAE came under scrutiny, as Denmark suspended the Emirati flights for five days. The European nation said that it barred the flights from the UAE due to growing suspicion of irregularities in the testing process being followed in the Gulf nation. Denmark's Minister of Transport, Benny Engelbrecht said that they were taking time to ensure that the negative tests of travelers from the Emirates were a real screening carried out appropriately.[247]

United States

Main article: COVID-19 testing in the United States

New York State

New York State's control measures consisted of PCR tests, stay-at-home measures and strengthening the healthcare system. On 29 February before its first case, the state allowed testing at the Wordsworth Center. They managed to convince the CDC to approve tests at state laboratories and the FDA to approve a test kit. As of 13 March the state was conducting more than 1,000 daily tests, growing to 10,000/day on 19 March. In April, the number exceeded 20,000. Many people queued at hospitals to get tested. On 21 March New York City health officials directed medical providers to test only those entering the hospital, for lack of PPE.[236][248][249][250][251][excessive citations]

USS Theodore Roosevelt

Main article: COVID-19 pandemic on USS Theodore Roosevelt

Following an outbreak, 94% of the 4,800 aircraft carrier crew were tested. Roughly 60 percent of the 600-plus sailors who tested positive were asymptomatic.[252] Five infected sailors who completed quarantine subsequently developed flu-like symptoms and again tested positive.[253]

Nevada

In 2020, Nevada received a donation of 250,000 Covid testing kits, which were a product of China's leading genetics company, BGI Group. A UAE-based firm owned by Tahnoun bin Zayed Al Nahyan, Group 42 partnered with the BGI Group to supply the testing kits to Nevada. However, the US Department of Homeland Security and the State Department raised a warning for Nevada hospitals to not use the Chinese-made testing kits, as there were concerns around the involvement of the Chinese government, test accuracy and privacy of the patients.[254]

Delayed testing

A shortage of trained medical laboratory scientists, assay reagents, analyzers, transport medium, and PPE coupled with high demand had limited initially limited the availability of testing and led to significantly increased turnaround times.[citation needed]

Testing statistics by country

Testing strategies vary by country and over time,[255] with some countries testing very widely,[8] while others have at times focused narrowly on only testing the seriously ill.[6] The country that tests only people showing symptoms will have a higher figure for "Confirmed"/"tested" than the country that also tests others.[256] If two countries are alike in every respect, including which people they test, the one that tests more people will have a higher "Confirmed / population". Studies have also found that countries that test more, relative to the number of deaths, have lower estimated case fatality rates[9] and younger age distributions of cases.[11]

COVID-19 testing statistics by country
Country or region Date[a] Tested Units[b] Confirmed
(cases) 		Confirmed /
tested,
% 		Tested /
population,
% 		Confirmed /
population,
% 		Ref.
  Afghanistan 17 Dec 2020 154,767 samples 49,621 32.1 0.40 0.13 [257]
  Albania 18 Feb 2021 428,654 samples 96,838 22.6 15.0 3.4 [258]
  Algeria 2 Nov 2020 230,553 samples 58,574 25.4 0.53 0.13 [259][260]
  Andorra 23 Feb 2022 300,307 samples 37,958 12.6 387 49.0 [261]
  Angola 2 Feb 2021 399,228 samples 20,981 5.3 1.3 0.067 [262]
  Antigua and Barbuda 6 Mar 2021 15,268 samples 832 5.4 15.9 0.86 [263]
  Argentina 16 Apr 2022 35,716,069 samples 9,060,495 25.4 78.3 20.0 [264]
  Armenia 29 May 2022 3,099,602 samples 422,963 13.6 105 14.3 [265]
  Australia 9 Sep 2022 78,548,492 samples 10,112,229 12.9 313 40.3 [266]
  Austria 1 Feb 2023 205,817,752 samples 5,789,991 2.8 2,312 65.0 [267]
  Azerbaijan 11 May 2022 6,838,458 samples 792,638 11.6 69.1 8.0 [268]
  Bahamas 28 Nov 2022 259,366 samples 37,483 14.5 67.3 9.7 [269]
  Bahrain 3 Dec 2022 10,578,766 samples 696,614 6.6 674 44.4 [270]
  Bangladesh 24 Jul 2021 7,417,714 samples 1,151,644 15.5 4.5 0.70 [271]
  Barbados 14 Oct 2022 770,100 samples 103,014 13.4 268 35.9 [272]
  Belarus 9 May 2022 13,217,569 samples 982,809 7.4 139 10.4 [273]
  Belgium 24 Jan 2023 36,548,544 samples 4,691,499 12.8 317 40.7 [274]
  Belize 8 Jun 2022 572,900 samples 60,694 10.6 140 14.9 [275][276]
  Benin 4 May 2021 595,112 samples 7,884 1.3 5.1 0.067 [277]
  Bhutan 28 Feb 2022 1,736,168 samples 12,702 0.73 234 1.71 [278]
  Bolivia 5 Jun 2022 4,358,669 cases 910,228 20.9 38.1 8.0 [279]
  Bosnia and Herzegovina 27 Sep 2022 1,872,934 samples 399,887 21.4 54.7 11.7 [280]
  Botswana 11 Jan 2022 2,026,898 232,432 11.5 89.9 10.3 [281][282]
  Brazil 19 Feb 2021 23,561,497 samples 10,081,676 42.8 11.2 4.8 [283][284]
  Brunei 2 Aug 2021 153,804 samples 338 0.22 33.5 0.074 [285]
  Bulgaria 2 Feb 2023 10,993,239 samples 1,295,524 11.8 158 18.6 [286]
  Burkina Faso 4 Mar 2021 158,777 samples 12,123 7.6 0.76 0.058 [259][287]
  Burundi 5 Jan 2021 90,019 884 0.98 0.76 0.0074 [288]
  Cambodia 1 Aug 2021 1,812,706 77,914 4.3 11.2 0.48 [289]
  Cameroon 18 Feb 2021 942,685 samples 32,681 3.5 3.6 0.12 [259]
  Canada 26 Nov 2022 66,343,123 samples 4,423,053 6.7 175 11.7 [290]
  Chad 2 Mar 2021 99,027 samples 4,020 4.1 0.72 0.029 [259][291]
  Chile 1 Feb 2023 48,154,268 samples 5,123,007 10.6 252 26.9 [292]
  China[c] 31 Jul 2020 160,000,000 cases 87,655 0.055 11.1 0.0061 [293][294]
  Colombia 24 Nov 2022 36,875,818 samples 6,314,769 17.1 76.4 13.1 [295][296]
  Costa Rica 2 Nov 2021 2,575,363 samples 561,054 21.8 51.5 11.2 [297]
  Croatia 2 Feb 2023 5,481,285 cases 1,267,798 23.1 134 31.1 [298]
  Cuba 2 Feb 2023 14,301,394 samples 1,112,470 7.8 126 9.8 [299][300]
  Cyprus[d] 29 Jan 2023 27,820,163 samples 644,160 2.3 3,223 74.4 [301]
  Czechia 1 Feb 2023 22,544,928 samples 4,590,529 20.4 211 42.9 [302]
  Denmark[e] 31 Jan 2023 67,682,707 samples 3,399,947 5.0 1,162 58.4 [303][304]
  Djibouti 28 Apr 2022 305,941 15,631 5.1 33.2 1.7 [305]
  Dominica 20 Jun 2022 209,803 cases 14,821 7.1 293 20.7 [306]
  Dominican Republic 22 Jul 2022 3,574,665 samples 626,030 17.5 32.9 5.8 [307]
  DR Congo 28 Feb 2021 124,838 25,961 20.8 0.14 0.029 [259][308]
  Ecuador 23 Jul 2021 1,627,189 samples 480,720 29.5 9.5 2.8 [309]
  Egypt 23 Jul 2021 3,137,519 samples 283,947 9.1 3.1 0.28 [259][310]
  El Salvador 18 Mar 2022 1,847,861 samples 161,052 8.7 28.5 2.5 [311]
  Equatorial Guinea 30 Jan 2023 403,773 17,113 4.2 30.8 1.3 [312]
  Estonia 31 Jan 2023 3,637,908 samples 613,954 16.9 274 46.2 [313]
  Eswatini 8 Dec 2021 415,110 49,253 11.9 36.5 4.3 [314]
  Ethiopia 24 Jun 2021 2,981,185 samples 278,446 9.3 2.6 0.24 [315]
  Faroe Islands 27 Feb 2022 774,000 samples 34,237 4.4 1,493 65.7 [316]
  Fiji 2 Jan 2023 667,953 samples 68,848 10.3 74.5 7.7 [317]
  Finland 14 Jan 2022 9,042,453 samples 371,135 4.1 163 6.7 [318]
  France[f][g] 15 May 2022 272,417,258 samples 29,183,646 10.7 417 44.7 [319]
  Gabon 23 Jul 2021 958,807 samples 25,325 2.6 3.1 0.082 [320]
  Gambia 15 Feb 2021 43,217 samples 4,469 10.3 2.0 0.21 [321]
  Georgia[h] 3 Nov 2021 4,888,787 samples 732,965 15.0 132 19.7 [322]
  Germany 7 Jul 2021 65,247,345 samples 3,733,519 5.7 77.8 4.5 [323][324]
  Ghana 3 Jul 2021 1,305,749 samples 96,708 7.4 4.2 0.31 [325]
  Greece 18 Dec 2022 101,576,831 samples 5,548,487 5.5 943 51.5 [326]
  Greenland 30 Jan 2022 164,573 samples 10,662 6.5 293 19.0 [327]
  Grenada 11 May 2021 28,684 161 0.56 25.7 0.14 [328]
  Guatemala 6 Jan 2023 6,800,560 samples 1,230,098 18.1 39.4 7.1 [329]
  Guinea 21 Jul 2021 494,898 samples 24,878 5.0 3.8 0.19 [259][330]
  Guinea-Bissau 7 Jul 2022 145,231 8,400 5.8 7.7 0.45 [331]
  Guyana 15 Jun 2022 648,569 cases 66,129 10.2 82.5 8.4 [332]
  Haiti 26 Nov 2022 223,475 cases 33,874 15.2 2.0 0.30 [333]
  Honduras 26 Nov 2021 1,133,782 samples 377,859 33.3 11.8 3.9 [334]
  Hungary 10 May 2022 11,394,556 samples 1,909,948 16.8 118 19.8 [335]
  Iceland 9 Aug 2022 1,988,652 samples 203,162 10.2 546 55.8 [336]
  India 8 Jul 2022 866,177,937 samples 43,585,554 5.0 63 31.7 [337][338]
  Indonesia 3 Jul 2023 76,062,770 cases 6,812,127 9.0 28.2 2.5 [339][340]
  Iran 31 May 2022 52,269,202 samples 7,232,268 13.8 62.8 8.7 [341]
  Iraq 3 Aug 2022 19,090,652 samples 2,448,484 12.8 47.5 6.1 [342]
  Ireland 31 Jan 2023 12,990,476 samples 1,700,817 13.1 264 34.6 [343]
  Israel 17 Jan 2022 41,373,364 samples 1,792,137 4.3 451 19.5 [344]
  Italy 16 Mar 2023 269,127,054 samples 25,651,205 9.5 446 42.5 [345]
  Ivory Coast 3 Mar 2021 429,177 samples 33,285 7.8 1.6 0.13 [346]
  Jamaica 30 Sep 2022 1,184,973 samples 151,931 12.8 43.5 5.6 [347]
  Japan 1 Mar 2021 8,487,288 432,773 5.1 6.7 0.34 [348]
  Jordan 6 Jun 2021 7,407,053 samples 739,847 10.0 69.5 6.9 [349]
  Kazakhstan 28 May 2021 11,575,012 samples 385,144 3.3 62.1 2.1 [350]
  Kenya 5 Mar 2021 1,322,806 samples 107,729 8.1 2.8 0.23 [351]
  Kosovo 31 May 2021 611,357 cases 107,410 17.6 33.8 5.9 [352]
  Kuwait 9 Mar 2022 7,754,247 samples 624,573 8.1 181 14.6 [353]
  Kyrgyzstan 10 Feb 2021 695,415 samples 85,253 12.3 10.7 1.3 [354]
  Laos 1 Mar 2021 114,030 cases 45 0.039 1.6 0.00063 [355]
  Latvia 5 Sep 2021 3,630,095 samples 144,518 4.0 189 7.5 [356]
  Lebanon 14 Jun 2021 4,599,186 samples 542,649 11.8 67.4 8.0 [357]
  Lesotho 30 Mar 2022 431,221 32,910 7.6 21.5 1.6 [358]
  Liberia 17 Jul 2021 128,246 5,396 4.2 2.5 0.11 [359]
  Libya 14 Apr 2022 2,578,215 samples 501,862 19.5 37.6 7.3 [259][360]
  Lithuania 31 Jan 2023 9,046,584 samples 1,170,108 12.9 324 41.9 [361][362]
  Luxembourg[i] 12 May 2022 4,248,188 samples 244,182 5.7 679 39.0 [363]
  Madagascar 19 Feb 2021 119,608 cases 19,831 16.6 0.46 0.076 [364]
  Malawi 29 Nov 2022 624,784 samples 88,086 14.1 3.3 0.46 [365]
  Malaysia 7 Sep 2021 23,705,425 cases 1,880,734 7.9 72.3 5.7 [366]
  Maldives 13 Mar 2022 2,216,560 samples 174,658 7.9 398 31.3 [367][368]
  Mali 7 Jul 2021 322,504 samples 14,449 4.5 1.6 0.071 [259][369]
  Malta 8 Sep 2021 1,211,456 samples 36,606 3.0 245 7.4 [370]
  Mauritania 16 Apr 2021 268,093 18,103 6.8 6.1 0.41 [371]
  Mauritius 22 Nov 2020 289,552 samples 494 0.17 22.9 0.039 [372]
  Mexico 15 Oct 2021 10,503,678 cases 3,749,860 35.7 8.2 2.9 [373]
  Moldova[j] 20 Apr 2022 3,213,594 samples 516,864 16.1 122 19.6 [374]
  Mongolia 10 Jul 2021 3,354,200 cases 136,053 4.1 100 4.1 [375]
  Montenegro 10 May 2021 394,388 samples 98,449 25.0 62.5 15.6 [376][377]
  Morocco 6 Jan 2023 14,217,563 cases 1,272,299 8.9 38.5 3.4 [378]
  Mozambique 22 Jul 2021 688,570 samples 105,866 15.4 2.2 0.34 [379]
  Myanmar 16 Sep 2021 4,047,680 samples 440,741 10.9 7.4 0.81 [380]
  Namibia 4 Jul 2022 1,062,663 samples 166,229 15.6 38.7 6.1 [381]
  Nepal 26 Jul 2022 5,804,358 samples 984,475 17.0 20.7 3.5 [382]
  Netherlands 6 Jul 2021 14,526,293 cases 1,692,834 11.7 83.4 9.7 [383]
  New Caledonia 3 Sep 2021 41,962 samples 136 0.32 15.7 0.050 [384]
  New Zealand 29 Jan 2023 7,757,935 samples 2,136,662 27.5 156 42.9 [385][386]
  Niger 22 Feb 2021 79,321 cases 4,740 6.0 0.35 0.021 [387]
  Nigeria 28 Feb 2021 1,544,008 samples 155,657 10.1 0.75 0.076 [388]
  North Korea 25 Nov 2020 16,914 cases 0 0 0.066 0 [389]
  North Macedonia 1 Jul 2021 881,870 samples 155,689 17.7 42.5 7.5 [390][391]
  Northern Cyprus[k] 12 Jul 2022 7,096,998 samples 103,034 1.5 2,177 31.6 [392]
  Norway 20 Jan 2022 9,811,888 samples 554,778 5.7 183 10.3 [393]
  Oman 28 Oct 2020 509,959 samples 114,434 22.4 11.0 2.5 [394]
  Pakistan 5 Mar 2021 9,173,593 samples 588,728 6.4 4.2 0.27 [395]
  Palestine 5 Feb 2022 3,078,533 samples 574,105 18.6 60.9 11.4 [396]
  Panama 28 Jan 2023 7,475,016 samples 1,029,701 13.8 179 24.7 [397]
  Papua New Guinea 17 Feb 2021 47,490 cases 961 2.0 0.53 0.011 [398]
  Paraguay 27 Mar 2022 2,609,819 samples 647,950 24.8 36.6 9.1 [399]
  Peru 17 Nov 2022 36,073,768 samples 4,177,786 11.6 109.9 12.7 [400]
  Philippines 7 Jan 2023 34,402,980 samples 4,073,980 11.8 34.1 4.0 [401][402]
  Poland 27 Apr 2022 36,064,311 samples 5,993,861 16.6 94.0 15.6 [403]
  Portugal 5 Jan 2022 27,515,490 samples 1,499,976 5.5 268 14.6 [404]
  Qatar 11 Nov 2022 4,061,988 cases 473,440 11.7 141 16.4 [405]
  Romania 29 Jan 2021 5,405,393 samples 724,250 13.4 27.9 3.7 [406]
  Russia 6 Jun 2022 295,542,733 samples 18,358,459 6.2 201 12.5 [407][408]
  Rwanda 6 Oct 2021 2,885,812 samples 98,209 3.4 22.3 0.76 [409]
  Saint Kitts and Nevis 26 Aug 2021 30,231 cases 995 3.3 57.6 1.9 [410]
  Saint Lucia 7 Oct 2022 212,132 samples 29,550 13.9 116.6 16.2 [411]
  Saint Vincent 28 Jan 2023 113,504 cases 9,585 8.4 103.0 8.7 [412]
  San Marino 29 Jan 2023 192,613 samples 23,427 12.2 563 68.4 [413]
  Saudi Arabia 26 Apr 2022 41,849,069 samples 753,632 1.8 120 2.2 [414]
  Senegal 12 Jul 2021 624,502 samples 46,509 7.4 3.9 0.29 [415]
  Serbia 2 Feb 2023 12,185,475 cases 2,473,599 20.3 175 35.5 [416]
  Singapore 3 Aug 2021 16,206,203 samples 65,315 0.40 284 1.1 [417][418]
  Slovakia 2 Feb 2023 7,391,882 samples 1,861,034 25.2 135 34.1 [419]
  Slovenia 2 Feb 2023 2,826,117 samples 1,322,282 46.8 135 63.1 [420]
  South Africa 24 May 2021 11,378,282 cases 1,637,848 14.4 19.2 2.8 [421][422]
  South Korea 1 Mar 2021 6,592,010 samples 90,029 1.4 12.7 0.17 [423]
  South Sudan 26 May 2021 164,472 10,688 6.5 1.3 0.084 [424]
  Spain 1 Jul 2021 54,128,524 samples 3,821,305 7.1 116 8.2 [425][426]
  Sri Lanka 30 Mar 2021 2,384,745 samples 93,128 3.9 10.9 0.43 [427][428]
  Sudan 7 Jan 2021 158,804 samples 23,316 14.7 0.36 0.053 [259]
  Sweden 24 May 2021 9,996,795 samples 1,074,751 10.8 96.8 10.4 [429][430]
  Switzerland[l] 7 Nov 2022 23,283,909 samples 4,276,836 18.4 270 49.7 [431]
  Taiwan[m] 3 Feb 2023 30,275,725 samples 8,622,129 28.48 128.3 36.528 [432]
  Tanzania 18 Nov 2020 3,880 509 13.1 0.0065 0.00085 [259]
  Thailand 4 Mar 2021 1,579,597 cases 26,162 1.7 2.3 0.038 [433]
  Togo 6 Jan 2023 807,269 39,358 4.9 9.4 0.46 [434]
  Trinidad and Tobago 3 Jan 2022 512,730 cases 92,997 18.1 37.6 6.8 [435]
  Tunisia 23 Aug 2021 2,893,625 samples 703,732 24.3 24.5 6.0 [436]
  Turkey 2 Jul 2021 61,236,294 samples 5,435,831 8.9 73.6 6.5 [437]
  Uganda 11 Feb 2021 852,444 samples 39,979 4.7 1.9 0.087 [438]
  Ukraine 24 Nov 2021 15,648,456 samples 3,367,461 21.5 37.2 8.0 [439]
  United Arab Emirates 1 Feb 2023 198,685,717 samples 1,049,537 0.53 2,070 10.9 [440]
  United Kingdom 19 May 2022 522,526,476 samples 22,232,377 4.3 774 32.9 [441]
  United States 29 Jul 2022 929,349,291 samples 90,749,469 9.8 281 27.4 [442][443]
  Uruguay 16 Apr 2022 6,089,116 samples 895,592 14.7 175 25.8 [444]
  Uzbekistan 7 Sep 2020 2,630,000 samples 43,975 1.7 7.7 0.13 [445]
  Venezuela 30 Mar 2021 3,179,074 samples 159,149 5.0 11.0 0.55 [446]
  Vietnam 28 Aug 2022 45,772,571 samples 11,403,302 24.9 46.4 11.6 [447]
  Zambia 10 Mar 2022 3,301,860 samples 314,850 9.5 19.0 1.8 [448]
  Zimbabwe 15 Oct 2022 2,529,087 samples 257,893 10.2 17.0 1.7 [259][449]
  1. ^ Local time.
  2. ^ For some countries it is unclear whether they report samples or cases. One person tested twice is recorded as one case and two samples.
  3. ^ Excluding Taiwan.
  4. ^ Excluding Northern Cyprus.
  5. ^ Excluding Greenland and the Faroe Islands.
  6. ^ Excluding Overseas France.
  7. ^ Testing data from 4 May to 12 May is missing because of the transition to the new reporting system SI-DEP.
  8. ^ Excluding Abkhazia and South Ossetia.
  9. ^ Data for residents only.
  10. ^ Excluding Transnistria.
  11. ^ Northern Cyprus is not recognized as a sovereign state by any country except Turkey.
  12. ^ Includes data for Liechtenstein.
  13. ^ Not a United Nations member.

See also

References

  •   This article incorporates public domain material from Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19. Centers for Disease Control and Prevention. Retrieved 5 May 2020.
  1. ^ "Coronavirus Disease 2019 (COVID-19)". U.S. Centers for Disease Control and Prevention (CDC). 11 February 2020. from the original on 14 March 2020. Retrieved 9 June 2020.
  2. ^ Kobokovich A, West R, Gronvall G. "Global Progress on COVID-19 Serology-Based Testing". Johns Hopkins Center for Health Security. from the original on 9 June 2020. Retrieved 9 June 2020.
  3. ^ a b c Kubina R, Dziedzic A (June 2020). "Molecular and Serological Tests for COVID-19 a Comparative Review of SARS-CoV-2 Coronavirus Laboratory and Point-of-Care Diagnostics". Diagnostics. 10 (6): 434. doi:10.3390/diagnostics10060434. PMC 7345211. PMID 32604919.
  4. ^ "Test for Past Infection". U.S. Centers for Disease Control and Prevention (CDC). 2020. from the original on 16 May 2020. Retrieved 19 May 2020. Antibody blood tests, also called antibody tests, check your blood by looking for antibodies, which show if you had a previous infection with the virus. Depending on when someone was infected and the timing of the test, the test may not find antibodies in someone with a current COVID-19 infection.
  5. ^ a b c Abbasi J (May 2020). "The Promise and Peril of Antibody Testing for COVID-19". JAMA. 323 (19): 1881–1883. doi:10.1001/jama.2020.6170. PMID 32301958. from the original on 20 April 2020. Retrieved 20 April 2020.
  6. ^ a b Brotschi M (7 March 2020). "Bund sucht nicht mehr alle Corona-Infizierten" [The federal government is no longer looking for all those infected with corona]. Der Bund (in German). ISSN 0774-6156. from the original on 29 March 2020. Retrieved 9 June 2020.
  7. ^ Van Beusekom M (24 March 2020). "Italian doctors note high COVID-19 death rate, urge action". CIDRAP News. from the original on 9 June 2020. Retrieved 9 June 2020.
  8. ^ a b Otmani M (22 March 2020). "COVID-19: First results of the voluntary screening in Iceland". Nordic Life Science. from the original on 29 March 2020. Retrieved 9 June 2020.
  9. ^ a b Ward D (April 2020). "Sampling bias: explaining wide variations in COVID-19 case fatality rates". Preprint. Bern, Switzerland: WardEnvironment. doi:10.13140/RG.2.2.24953.62564/1.
  10. ^ Henriques M (2 April 2020). "Coronavirus: Why death and mortality rates differ". BBC News. from the original on 2 April 2020. Retrieved 9 June 2020.
  11. ^ a b Ward D (May 2020). Sampling Bias: Explaining Variations in Age Distributions of COVID-19 Cases. Technical Report (Report). WardEnvironment. doi:10.13140/RG.2.2.27321.19047/2.
  12. ^ "Why More Younger People Are Testing Positive for COVID-19". Time. from the original on 26 February 2021. Retrieved 18 August 2020.
  13. ^ Mina MJ, Parker R, Larremore DB (November 2020). "Rethinking Covid-19 Test Sensitivity - A Strategy for Containment". The New England Journal of Medicine. 383 (22): e120. doi:10.1056/NEJMp2025631. PMID 32997903. S2CID 222158786.
  14. ^ a b "Antigen-detection in the diagnosis of SARS-CoV-2 infection". www.who.int. Retrieved 12 July 2022.
  15. ^ a b c CDC (11 February 2020). "Guidance for Antigen Testing for SARS-CoV-2 for Healthcare Providers Testing Individuals in the Community". Centers for Disease Control and Prevention. Retrieved 12 July 2022.
  16. ^ "Siouxsie Wiles & Toby Morris: What we don't know about Covid-19". The Spinoff. 6 May 2020. from the original on 22 August 2020. Retrieved 6 May 2020.
  17. ^ "Testing for COVID-19". U.S. Centers for Disease Control and Prevention (CDC). 20 May 2020. from the original on 19 May 2020. Retrieved 20 May 2020. Two kinds of tests are available for COVID-19: viral tests and antibody tests.
  18. ^ Tanner T (23 September 2020). "Finland deploys coronavirus-sniffing dogs at main airport". Associated Press. Helsinki. from the original on 27 October 2020. Retrieved 28 October 2020.
  19. ^ Jones RT, Guest C, Lindsay SW, Kleinschmidt I, Bradley J, Dewhirst S, et al. (December 2020). "Could bio-detection dogs be used to limit the spread of COVID-19 by travellers?". Journal of Travel Medicine. 27 (8). doi:10.1093/jtm/taaa131. PMC 7454791. PMID 32789466.
  20. ^ Jendrny P, Schulz C, Twele F, Meller S, von Köckritz-Blickwede M, Osterhaus AD, et al. (July 2020). "Scent dog identification of samples from COVID-19 patients - a pilot study". BMC Infectious Diseases. 20 (1): 536. doi:10.1186/s12879-020-05281-3. PMC 7376324. PMID 32703188.
  21. ^ a b Habibzadeh P, Mofatteh M, Silawi M, Ghavami S, Faghihi MA (September 2021). "Molecular diagnostic assays for COVID-19: an overview". Critical Reviews in Clinical Laboratory Sciences. 58 (6): 385–398. doi:10.1080/10408363.2021.1884640. PMC 7898297. PMID 33595397.
  22. ^ "RNA Extraction". AssayGenie. from the original on 6 May 2020. Retrieved 7 May 2020.
  23. ^ a b "How is the COVID-19 Virus Detected using Real Time RT-PCR?". IAEA. 27 March 2020. from the original on 1 May 2020. Retrieved 5 May 2020.
  24. ^ "Curetis Group Company Ares Genetics and BGI Group Collaborate to Offer Next-Generation Sequencing and PCR-based Coronavirus (2019-nCoV) Testing in Europe". GlobeNewswire News Room (Press release). 30 January 2020. from the original on 31 January 2020. Retrieved 1 February 2020.
  25. ^ a b Bustin SA, Benes V, Garson JA, Hellemans J, Huggett J, Kubista M, et al. (April 2009). "The MIQE guidelines: minimum information for publication of quantitative real-time PCR experiments". Clinical Chemistry. 55 (4): 611–622. doi:10.1373/clinchem.2008.112797. PMID 19246619.
  26. ^ "Real-time reverse transcription PCR (qRT-PCR) and its potential use in clinical diagnosis" (PDF). Clinical Science. 23 September 2005. (PDF) from the original on 24 November 2020. Retrieved 5 May 2020.
  27. ^ "The Basics: RT-PCR". ThermoFisher Scientific. from the original on 14 April 2020. Retrieved 5 May 2020.
  28. ^ Kang XP, Jiang T, Li YQ, Lin F, Liu H, Chang GH, et al. (June 2010). "A duplex real-time RT-PCR assay for detecting H5N1 avian influenza virus and pandemic H1N1 influenza virus". Virology Journal. 7: 113. doi:10.1186/1743-422X-7-113. PMC 2892456. PMID 20515509.
  29. ^ Joyce C (2002). "Quantitative RT-PCR: A Review of Current Methodologies". RT-PCR Protocols. Methods Mol. Biol. Vol. 193. pp. 83–92. doi:10.1385/1-59259-283-X:083. ISBN 978-1-59259-283-8. PMID 12325527.
  30. ^ Varkonyi-Gasic E, Hellens RP (2010). "QRT-PCR of Small RNAs". Plant Epigenetics. Methods in Molecular Biology. Vol. 631. pp. 109–22. doi:10.1007/978-1-60761-646-7_10. ISBN 978-1-60761-645-0. PMID 20204872.
  31. ^ "Accelerated Emergency Use Authorization (Eua) Summary Covid-19 Rt-Pcr Test (Laboratory Corporation of America)". FDA. from the original on 16 January 2021. Retrieved 3 April 2020.
  32. ^ Taylor S, Wakem M, Dijkman G, Alsarraj M, Nguyen M (April 2010). "A practical approach to RT-qPCR-Publishing data that conform to the MIQE guidelines". Methods. 50 (4): S1–S5. doi:10.1016/j.ymeth.2010.01.005. PMID 20215014.
  33. ^ Dinnes J, Deeks JJ, Berhane S, Taylor M, Adriano A, Davenport C, et al. (March 2021). "Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection". The Cochrane Database of Systematic Reviews. 3 (4): CD013705. doi:10.1002/14651858.CD013705.pub2. PMC 8078597. PMID 33760236.
  34. ^ Dinnes J, Sharma P, Berhane S, van Wyk SS, Nyaaba N, Domen J, et al. (July 2022). "Rapid, point-of-care antigen tests for diagnosis of SARS-CoV-2 infection". The Cochrane Database of Systematic Reviews. 2022 (7): CD013705. doi:10.1002/14651858.CD013705.pub3. PMC 9305720. PMID 35866452.
  35. ^ "Real-Time RT-PCR Panel for Detection 2019-nCoV". U.S. Centers for Disease Control and Prevention (CDC). 29 January 2020. from the original on 30 January 2020. Retrieved 1 February 2020.
  36. ^ a b c Drosten C (26 March 2020). "Coronavirus-Update Folge 22" [Coronavirus update episode 22] (PDF). NDR. (PDF) from the original on 31 March 2020. Retrieved 2 April 2020.
  37. ^ a b "Here's where things stand on COVID-19 tests in the U.S." Science News. ScienceNews. 17 April 2020. from the original on 28 April 2020. Retrieved 6 May 2020.
  38. ^ a b c Xu R, Cui B, Duan X, Zhang P, Zhou X, Yuan Q (April 2020). "Saliva: potential diagnostic value and transmission of 2019-nCoV". International Journal of Oral Science. 12 (1): 11. doi:10.1038/s41368-020-0080-z. PMC 7162686. PMID 32300101.
  39. ^ Drosten C, Günther S, Preiser W, van der Werf S, Brodt HR, Becker S, et al. (May 2003). "Identification of a novel coronavirus in patients with severe acute respiratory syndrome". The New England Journal of Medicine. 348 (20): 1967–1976. doi:10.1056/NEJMoa030747. hdl:1765/8447. PMID 12690091.
  40. ^ Ghoshal U, Vasanth S, Tejan N (June 2020). "A guide to laboratory diagnosis of Corona Virus Disease-19 for the gastroenterologists". Indian Journal of Gastroenterology. 39 (3): 236–242. doi:10.1007/s12664-020-01082-3. PMC 7462729. PMID 32875524.
  41. ^ "COVID-19 saliva tests: What is the benefit?". Mayo Clinic. 16 April 2020. from the original on 1 May 2020. Retrieved 6 May 2020.
  42. ^ a b "New Rutgers Saliva Test for Coronavirus Gets FDA Approval". Rutgers.edu. 13 April 2020. from the original on 30 April 2020. Retrieved 1 May 2020.
  43. ^ "FDA authorizes Covid-19 saliva test for emergency use". CNN. 14 April 2020. from the original on 27 April 2020. Retrieved 1 May 2020.
  44. ^ Wyllie AL, Fournier J, Casanovas-Massana A, Campbell M, Tokuyama M, Vijayakumar P, et al. (September 2020). "Saliva or Nasopharyngeal Swab Specimens for Detection of SARS-CoV-2". The New England Journal of Medicine. 383 (13): 1283–1286. doi:10.1056/NEJMc2016359. PMC 7484747. PMID 32857487. S2CID 221358482.
  45. ^ Service RF (August 2020). "Spit shines for easier coronavirus testing". Science. 369 (6507): 1041–1042. Bibcode:2020Sci...369.1041S. doi:10.1126/science.369.6507.1041. PMID 32855317. S2CID 221358939.
  46. ^ "Yale University School of Public Health finds saliva samples promising alternative to nasopharyngeal swab". Merck Manual. 29 April 2020. from the original on 28 May 2020. Retrieved 6 April 2020.
  47. ^ "FDA gives emergency approval to 'game changer' COVID-19 saliva test". The Washington Times. from the original on 16 August 2020. Retrieved 15 August 2020.
  48. ^ "Coronavirus (COVID-19) Update: FDA Issues Emergency Use Authorization to Yale School of Public Health for SalivaDirect, Which Uses a New Method of Saliva Sample Processing". U.S. Food and Drug Administration (FDA) (Press release). 15 August 2020. from the original on 16 August 2020. Retrieved 6 November 2020.
  49. ^ a b   One or more of the preceding sentences incorporates text from this source, which is in the public domain: "Risk of False Results with the Curative SARS-Cov-2 Test for COVID-19". U.S. Food and Drug Administration (FDA). 4 January 2021. from the original on 4 January 2021. Retrieved 4 January 2021.
  50. ^ Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19 (2020) referenced
    • CDC unpublished data
    • COVID-19 Investigation Team (June 2020). "Clinical and virologic characteristics of the first 12 patients with coronavirus disease 2019 (COVID-19) in the United States". Nature Medicine. 26 (6): 861–868. doi:10.1038/s41591-020-0877-5. PMID 32327757.{{cite journal}}: CS1 maint: numeric names: authors list (link)
    • Young BE, Ong SW, Kalimuddin S, Low JG, Tan SY, Loh J, et al. (April 2020). "Epidemiologic Features and Clinical Course of Patients Infected With SARS-CoV-2 in Singapore". JAMA. 323 (15): 1488–1494. doi:10.1001/jama.2020.3204. PMC 7054855. PMID 32125362.
    • Zou L, Ruan F, Huang M, Liang L, Huang H, Hong Z, et al. (March 2020). "SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients". The New England Journal of Medicine. 382 (12): 1177–1179. doi:10.1056/NEJMc2001737. PMC 7121626. PMID 32074444.
    • Wölfel R, Corman VM, Guggemos W, Seilmaier M, Zange S, Müller MA, et al. (May 2020). "Virological assessment of hospitalized patients with COVID-2019". Nature. 581 (7809): 465–469. Bibcode:2020Natur.581..465W. doi:10.1038/s41586-020-2196-x. PMID 32235945.
  51. ^ Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19 (2020) referenced
  52. ^ Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19 (2020) referenced
    • CDC unpublished data
    • COVID-19 Investigation Team (June 2020). "Clinical and virologic characteristics of the first 12 patients with coronavirus disease 2019 (COVID-19) in the United States". Nature Medicine. 26 (6): 861–868. doi:10.1038/s41591-020-0877-5. PMID 32327757.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  53. ^ Zimmer C (5 May 2020). "With Crispr, a Possible Quick Test for the Coronavirus". The New York Times. ISSN 0362-4331. from the original on 14 May 2020. Retrieved 14 May 2020.
  54. ^ "STOPCovid". stopcovid.science. from the original on 10 June 2020. Retrieved 14 June 2020.
  55. ^ Joung J, Ladha A, Saito M, Segel M, Bruneau R, Huang MW, et al. (May 2020). "Point-of-care testing for COVID-19 using SHERLOCK diagnostics". medRxiv 10.1101/2020.05.04.20091231v1.
  56. ^ a b c d e f "Developing Antibodies and Antigens for COVID-19 Diagnostics". Technology Networks. 6 April 2020. from the original on 30 April 2020. Retrieved 30 April 2020.
  57. ^ Guglielmi G (September 2020). "Fast coronavirus tests: what they can and can't do". Nature. 585 (7826): 496–498. Bibcode:2020Natur.585..496G. doi:10.1038/d41586-020-02661-2. PMID 32939084. S2CID 221768935.
  58. ^ CDC (11 February 2020). "COVID-19 and Your Health". Centers for Disease Control and Prevention. Retrieved 12 July 2022.
  59. ^ "Remarks by President Trump, Vice President Pence, and Members of the Coronavirus Task Force in Press Briefing". whitehouse.gov. 17 April 2020. from the original on 20 January 2021. Retrieved 30 April 2020 – via National Archives.
  60. ^ Müllender F (11 March 2021). "Grundschulen – Corona-Pool-Tests gelten als kindgerecht, unkompliziert und sicher" (in German). Deutschlandfunk. from the original on 24 July 2021. Retrieved 5 June 2021.
  61. ^ "NIH launches competition to speed COVID-19 diagnostics". AAAS. 29 April 2020. from the original on 1 May 2020. Retrieved 1 May 2020.
  62. ^ a b "What to know about the three main types of coronavirus tests". CNN. 29 April 2020. from the original on 10 May 2020. Retrieved 30 April 2020.
  63. ^ a b Dinnes J, Deeks JJ, Berhane S, Taylor M, Adriano A, Davenport C, et al. (Cochrane COVID-19 Diagnostic Test Accuracy Group) (March 2021). "Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection". The Cochrane Database of Systematic Reviews. 3 (3): CD013705. doi:10.1002/14651858.CD013705.pub2. PMC 8078597. PMID 33760236.
  64. ^ "Rapid Tests". Rapid Tests. from the original on 31 May 2021. Retrieved 2 July 2021.
  65. ^ Shaw J (3 August 2020). "Failing the Coronavirus-Testing Test". Harvard Magazine. from the original on 30 June 2021. Retrieved 2 July 2021.
  66. ^ a b Office of the Commissioner (9 May 2020). "Coronavirus (COVID-19) Update: FDA Authorizes First Antigen Test to Help in the Rapid Detection of the Virus that Causes COVID-19 in Patients". FDA. from the original on 29 May 2021. Retrieved 2 July 2021.
  67. ^ a b c d Klasse PJ (9 September 2014). "Neutralization of Virus Infectivity by Antibodies: Old Problems in New Perspectives". Advances in Biology. 2014. Hindawi Limited: 1–24. doi:10.1155/2014/157895. PMC 4835181. PMID 27099867.
  68. ^ "The next frontier in coronavirus testing: Identifying the full scope of the pandemic, not just individual infections". STAT. 27 March 2020. from the original on 29 June 2020. Retrieved 30 April 2020.
  69. ^ a b Tang EW, Bobenchik AM, Lu S (September 2020). "Testing for SARS-CoV-2 (COVID-19): A General Review". Rhode Island Medical Journal. 103 (8): 20–23. PMID 32900007.
  70. ^ "What Immunity to COVID-19 Really Means". Scientific American. 10 April 2020. from the original on 28 April 2020.
  71. ^ a b Fox, Tilly; Geppert, Julia; Dinnes, Jacqueline; Scandrett, Katie; Bigio, Jacob; Sulis, Giorgia; Hettiarachchi, Dineshani; Mathangasinghe, Yasith; Weeratunga, Praveen; Wickramasinghe, Dakshitha; Bergman, Hanna; Buckley, Brian S.; Probyn, Katrin; Sguassero, Yanina; Davenport, Clare (17 November 2022). "Antibody tests for identification of current and past infection with SARS-CoV-2". The Cochrane Database of Systematic Reviews. 2022 (11): CD013652. doi:10.1002/14651858.CD013652.pub2. ISSN 1469-493X. PMC 9671206. PMID 36394900.
  72. ^ "Cellex Emergency Use Authorization". FDA. 1 April 2020. from the original on 9 April 2020. Retrieved 10 April 2020.
  73. ^ "Will an Antibody Test Allow Us to Go Back to School or Work?". The New York Times. 10 April 2020. from the original on 15 April 2020. Retrieved 15 April 2020.
  74. ^ "Mount Sinai Emergency Use Authorization". FDA. 15 April 2020. Retrieved 18 April 2020.
  75. ^ Bauer G (January 2021). "The variability of the serological response to SARS-corona virus-2: Potential resolution of ambiguity through determination of avidity (functional affinity)". Journal of Medical Virology. 93 (1): 311–322. doi:10.1002/jmv.26262. PMC 7361859. PMID 32633840.
  76. ^ Ravi N, Cortade DL, Ng E, Wang SX (October 2020). "Diagnostics for SARS-CoV-2 detection: A comprehensive review of the FDA-EUA COVID-19 testing landscape". Biosensors & Bioelectronics. 165: 112454. doi:10.1016/j.bios.2020.112454. PMC 7368663. PMID 32729549.
  77. ^ Goudouris ES (2020). "Laboratory diagnosis of COVID-19". Jornal de Pediatria. 97 (1): 7–12. doi:10.1016/j.jped.2020.08.001. PMC 7456621. PMID 32882235.
  78. ^ a b c d "Global Progress on COVID-19 Serology-Based Testing". Johns Hopkins Center for Health Security. from the original on 14 June 2020. Retrieved 14 June 2020.
  79. ^ a b Tan CW, Chia WN, Qin X, Liu P, Chen MI, Tiu C, et al. (September 2020). "A SARS-CoV-2 surrogate virus neutralization test based on antibody-mediated blockage of ACE2-spike protein-protein interaction". Nature Biotechnology. 38 (9): 1073–1078. doi:10.1038/s41587-020-0631-z. PMID 32704169. S2CID 220720953.
  80. ^ a b c Mallapaty S (April 2020). "Will antibody tests for the coronavirus really change everything?". Nature. 580 (7805): 571–572. Bibcode:2020Natur.580..571M. doi:10.1038/d41586-020-01115-z. PMID 32313159. S2CID 216048544. from the original on 24 June 2020. Retrieved 20 April 2020.
  81. ^ a b c "Q&A on COVID-19 Antibody Tests". factcheck.org. 27 April 2020. from the original on 27 April 2020. Retrieved 28 April 2020.
  82. ^ "Neutralising antibody". Biology-Online. 2008. from the original on 8 July 2018. Retrieved 4 July 2009.
  83. ^ Schmaljohn AL (July 2013). "Protective antiviral antibodies that lack neutralizing activity: precedents and evolution of concepts". Current HIV Research. 11 (5): 345–353. doi:10.2174/1570162x113116660057. PMID 24191933.
  84. ^ Rhorer J, Ambrose CS, Dickinson S, Hamilton H, Oleka NA, Malinoski FJ, Wittes J (February 2009). "Efficacy of live attenuated influenza vaccine in children: A meta-analysis of nine randomized clinical trials". Vaccine. 27 (7). Virology Blog: 1101–1110. doi:10.1016/j.vaccine.2008.11.093. PMID 19095024. from the original on 23 April 2020. Retrieved 29 April 2020.
  85. ^ "expert reaction to announcement by Roche of its new serology test for COVID-19 antibodies". Science Media Centre. 17 April 2020. from the original on 30 April 2020. Retrieved 28 April 2020.
  86. ^ Cao WC, Liu W, Zhang PH, Zhang F, Richardus JH (September 2007). "Disappearance of antibodies to SARS-associated coronavirus after recovery". The New England Journal of Medicine. 357 (11). NEJM: 1162–1163. doi:10.1056/NEJMc070348. PMID 17855683.
  87. ^ a b "Lack of Peripheral Memory B Cell Responses in Recovered Patients with Severe Acute Respiratory Syndrome: A Six-Year Follow-Up Study" (PDF). Journal of Immunology. 19 April 2011. (PDF) from the original on 1 May 2020. Retrieved 1 May 2020.
  88. ^ Leslie M (May 2020). "T cells found in coronavirus patients 'bode well' for long-term immunity". Science. 368 (6493): 809–810. Bibcode:2020Sci...368..809L. doi:10.1126/science.368.6493.809. PMID 32439770. S2CID 218834495.
  89. ^ Calvo-Henriquez C, Maldonado-Alvarado B, Chiesa-Estomba C, Rivero-Fernández I, Sanz-Rodriguez M, Villarreal IM, et al. (October 2020). "Ethyl alcohol threshold test: a fast, reliable and affordable olfactory Assessment tool for COVID-19 patients". European Archives of Oto-Rhino-Laryngology. 277 (10): 2783–2792. doi:10.1007/s00405-020-06131-3. PMC 7312102. PMID 32583183.
  90. ^ Hayes J, Exten C, State P (24 December 2020). "At-home DIY smell tests could catch Covid-19 cases". CNN Health. The Conversation. Retrieved 7 September 2021.
  91. ^ Menni C, Sudre CH, Steves CJ, Ourselin S, Spector TD (November 2020). "Widespread smell testing for COVID-19 has limited application - Authors' reply". Lancet. 396 (10263): 1630–1631. doi:10.1016/S0140-6736(20)32316-3. PMC 7832202. PMID 33157000.
  92. ^ a b c Salehi S, Abedi A, Balakrishnan S, Gholamrezanezhad A (July 2020). "Coronavirus Disease 2019 (COVID-19): A Systematic Review of Imaging Findings in 919 Patients". AJR. American Journal of Roentgenology. 215 (1): 87–93. doi:10.2214/AJR.20.23034. PMID 32174129. Known features of COVID-19 on initial CT include bilateral multilobar ground-glass opacification (GGO) with a peripheral or posterior distribution, mainly in the lower lobes and less frequently within the right middle lobe.
  93. ^ Manigandan S, Wu MT, Ponnusamy VK, Raghavendra VB, Pugazhendhi A, Brindhadevi K (November 2020). "A systematic review on recent trends in transmission, diagnosis, prevention and imaging features of COVID-19". Process Biochemistry. 98: 233–240. doi:10.1016/j.procbio.2020.08.016. PMC 7439988. PMID 32843849.
  94. ^ Lee EY, Ng MY, Khong PL (April 2020). "COVID-19 pneumonia: what has CT taught us?". The Lancet. Infectious Diseases. 20 (4): 384–385. doi:10.1016/S1473-3099(20)30134-1. PMC 7128449. PMID 32105641.
  95. ^ "ACR Recommendations for the use of Chest Radiography and Computed Tomography (CT) for Suspected COVID-19 Infection". American College of Radiology. 22 March 2020. from the original on 13 May 2020. Retrieved 20 May 2020.
  96. ^ a b c Tabik S, Gomez-Rios A, Martin-Rodriguez JL, Sevillano-Garcia I, Rey-Area M, Charte D, et al. (December 2020). "COVIDGR Dataset and COVID-SDNet Methodology for Predicting COVID-19 Based on Chest X-Ray Images". IEEE Journal of Biomedical and Health Informatics. 24 (12): 3595–3605. doi:10.1109/JBHI.2020.3037127. hdl:10045/110797. PMC 8545181. PMID 33170789. S2CID 219179286.
January 01, 1970
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COVID 19 testing involves analyzing samples to assess the current or past presence of SARS CoV 2 The two main types of tests detect either the presence of the virus or antibodies produced in response to infection 1 2 Molecular tests for viral presence through its molecular components are used to diagnose individual cases and to allow public health authorities to trace and contain outbreaks Antibody tests serology immunoassays instead show whether someone once had the disease 3 They are less useful for diagnosing current infections because antibodies may not develop for weeks after infection 4 It is used to assess disease prevalence which aids the estimation of the infection fatality rate 5 The US CDC s COVID 19 laboratory test kit Individual jurisdictions have adopted varied testing protocols including whom to test how often to test analysis protocols sample collection and the uses of test results 6 7 8 This variation has likely significantly impacted reported statistics including case and test numbers case fatality rates and case demographics 9 10 11 12 Because SARS CoV 2 transmission occurs days after exposure and before onset of symptoms there is an urgent need for frequent surveillance and rapid availability of results 13 Test analysis is often performed in automated high throughput medical laboratories by medical laboratory scientists Rapid self tests and point of care testing are also available and can offer a faster and less expensive method to test for the virus although with a lower accuracy 14 15 Contents 1 Methods 1 1 Detection of the virus 1 1 1 Reverse transcription polymerase chain reaction RT PCR test 1 1 2 Other molecular tests 1 1 3 Antigen tests 1 2 Antibody tests 1 2 1 Antibody Test Types 1 2 1 1 Rapid diagnostic test RDT 1 2 1 2 Enzyme linked immunosorbent assay ELISA 1 2 1 3 Neutralization assay 1 2 1 4 Chemiluminescent immunoassay 1 2 2 Neutralizing vis a vis binding antibodies 1 3 Other tests 1 3 1 Sniff tests 1 3 2 Imaging 1 3 3 Serology CoLab score tests 1 3 4 Breath tests 1 3 5 Animals 1 3 6 Functional assays 2 History 3 Testing protocols 3 1 Drive through testing 3 2 Home collection 3 3 Pooled testing 3 4 Multi tiered testing 3 5 Required volume 3 5 1 United States 3 6 Snapshot mass testing 3 7 Surveillance and screening of populations 4 Available tests 4 1 Nucleic acid tests 4 2 Antigen tests 4 3 Serology antibody tests 5 Accuracy 5 1 Sensitivity and specificity 5 2 Causes of test error 5 3 PCR based test 5 4 Isothermal nucleic amplification test 6 Confirmatory testing 7 National or regional responses 7 1 Iceland 7 2 India 7 3 Italy 7 4 Japan 7 5 Russia 7 6 Singapore 7 7 Slovakia 7 8 South Korea 7 9 Taiwan 7 10 United Arab Emirates 7 11 United States 7 11 1 New York State 7 11 2 USS Theodore Roosevelt 7 11 3 Nevada 7 11 4 Delayed testing 8 Testing statistics by country 9 See also 10 References 11 Further reading 12 External linksMethods nbsp Explanation of the underlying pathophysiology pertaining to diagnosis of COVID 19 16 Positive viral tests indicate a current infection while positive antibody tests indicate a prior infection 17 Other techniques include a CT scan checking for elevated body temperature checking for low blood oxygen level and detection by trained dogs 18 19 20 Detection of the virus Detection of the virus is usually done either by looking for the virus s inner RNA or pieces of protein on the outside of the virus Tests that look for the viral antigens parts of the virus are called antigen tests There are multiple types of tests that look for the virus by detecting the presence of the virus s RNA These are called nucleic acid or molecular tests after molecular biology As of 2021 update the most common form of molecular test is the reverse transcription polymerase chain reaction RT PCR test 21 Other methods used in molecular tests include CRISPR isothermal nucleic acid amplification digital polymerase chain reaction microarray analysis and next generation sequencing 21 Reverse transcription polymerase chain reaction RT PCR test Polymerase chain reaction PCR is a process that amplifies replicates a small well defined segment of DNA many hundreds of thousands of times creating enough of it for analysis Test samples are treated with certain chemicals 22 23 that allow DNA to be extracted Reverse transcription converts RNA into DNA Reverse transcription polymerase chain reaction RT PCR first uses reverse transcription to obtain DNA followed by PCR to amplify that DNA creating enough to be analyzed 23 RT PCR can thereby detect SARS CoV 2 which contains only RNA The RT PCR process generally requires a few hours 24 These tests are also referred to as molecular or genetic assays 3 Real time PCR qPCR 25 provides advantages including automation higher throughput and more reliable instrumentation It has become the preferred method 26 27 The combined technique has been described as real time RT PCR 28 or quantitative RT PCR 29 and is sometimes abbreviated qRT PCR 30 rRT PCR 31 or RT qPCR 32 although sometimes RT PCR or PCR are used The Minimum Information for Publication of Quantitative Real Time PCR Experiments MIQE guidelines propose the term RT qPCR 25 but not all authors adhere to this Average sensitivity for rapid molecular tests depend on the brand For ID NOW the average sensitivity was 73 0 with an average specificity of 99 7 for Xpert Xpress the average sensitivity was 100 with an average specificity of 97 2 33 34 In a diagnostic test sensitivity is a measure of how well a test can identify true positives and specificity is a measure of how well a test can identify true negatives For all testing both diagnostic and screening there is usually a trade off between sensitivity and specificity such that higher sensitivities will mean lower specificities and vice versa nbsp Sensitivity and SpecificityA 90 specific test will correctly identify 90 of those who are uninfected leaving 10 with a false positive result Samples can be obtained by various methods including a nasopharyngeal swab sputum coughed up material 35 throat swabs 36 deep airway material collected via suction catheter 36 or saliva 37 38 Drosten et al remarked that for 2003 SARS from a diagnostic point of view it is important to note that nasal and throat swabs seem less suitable for diagnosis since these materials contain considerably less viral RNA than sputum and the virus may escape detection if only these materials are tested 39 Sensitivity of clinical samples by RT PCR is 63 for nasal swab 32 for pharyngeal swab 48 for feces 72 75 for sputum and 93 95 for bronchoalveolar lavage 40 The likelihood of detecting the virus depends on collection method and how much time has passed since infection According to Drosten tests performed with throat swabs are reliable only in the first week Thereafter the virus may abandon the throat and multiply in the lungs In the second week sputum or deep airways collection is preferred 36 Collecting saliva may be as effective as nasal and throat swabs 37 although this is not certain 41 38 Sampling saliva may reduce the risk for health care professionals by eliminating close physical interaction 42 It is also more comfortable for the patient 43 Quarantined people can collect their own samples 42 A saliva test s diagnostic value depends on sample site deep throat oral cavity or salivary glands 38 Some studies have found that saliva yielded greater sensitivity and consistency when compared with swab samples 44 45 46 On 15 August 2020 the US FDA granted an emergency use authorization for a saliva test developed at Yale University that gives results in hours 47 48 On 4 January 2021 the US FDA issued an alert about the risk of false results particularly false negative results with the Curative SARS Cov 2 Assay real time RT PCR test 49 Viral burden measured in upper respiratory specimens declines after symptom onset 50 Following recovery many patients no longer have detectable viral RNA in upper respiratory specimens Among those who do RNA concentrations three days following recovery are generally below the range in which replication competent virus has been reliably isolated 51 No clear correlation has been described between length of illness and duration of post recovery shedding of viral RNA in upper respiratory specimens 52 nbsp Demonstration of a nasopharyngeal swab for COVID 19 testing nbsp Demonstration of a throat swab for COVID 19 testing nbsp A PCR machine source source source source source source Video of a nasopharyngeal swab for COVID 19 testing Other molecular tests Isothermal nucleic acid amplification tests also amplify the virus s genome They are faster than PCR because they do not involve repeated heating and cooling cycles These tests typically detect DNA using fluorescent tags which are read out with specialized machines citation needed CRISPR gene editing technology was modified to perform the detection if the CRISPR enzyme attaches to the sequence it colors a paper strip The researchers expect the resulting test to be cheap and easy to use in point of care settings 53 54 The test amplifies RNA directly without the RNA to DNA conversion step of RT PCR 55 Antigen tests nbsp COVID 19 Antigen Rapid Test Kit the timer is provided by the user nbsp Mucus from nose or throat in a test liquid is placed onto a COVID 19 rapid antigen diagnostic test device nbsp COVID 19 rapid testing in Rwanda An antigen is the part of a pathogen that elicits an immune response Antigen tests look for antigen proteins from the viral surface In the case of a coronavirus these are usually proteins from the surface spikes 56 SARS CoV 2 antigens can be detected before onset of COVID 19 symptoms as soon as SARS CoV 2 virus particles with more rapid test results but with less sensitivity than PCR tests for the virus 57 COVID 19 rapid antigen tests are lateral flow immunoassays that detect the presence of a specific viral antigen which indicates current viral infection Antigen tests produce results quickly within approximately 15 30 minutes and most can be used at the point of care or as self tests Self tests are rapid tests that can be taken at home or anywhere are easy to use and produce rapid results 58 Antigen tests can be performed on nasopharyngeal nasal swab or saliva specimens 15 Antigen tests that can identify SARS CoV 2 offer a faster and less expensive method to test for the virus 14 Antigen tests are generally less sensitive than real time reverse transcription polymerase chain reaction RT PCR and other nucleic acid amplification tests NAATs 15 Antigen tests may be one way to scale up testing to much greater levels 56 Isothermal nucleic acid amplification tests can process only one sample at a time per machine RT PCR tests are accurate but require too much time energy and trained personnel to run the tests 56 There will never be the ability on a PCR test to do 300 million tests a day or to test everybody before they go to work or to school Deborah Birx head of the White House Coronavirus Task Force said on 17 April 2020 But there might be with the antigen test 59 Samples may be collected via nasopharyngeal swab a swab of the anterior nares or from saliva obtained by various methods including lollipop tests for children 60 The sample is then exposed to paper strips containing artificial antibodies designed to bind to coronavirus antigens Antigens bind to the strips and give a visual readout The process takes less than 30 minutes can deliver results at point of care and does not require expensive equipment or extensive training 56 Swabs of respiratory viruses often lack enough antigen material to be detectable 61 This is especially true for asymptomatic patients who have little if any nasal discharge Viral proteins are not amplified in an antigen test 56 62 A Cochrane review based on 64 studies investigating the efficacy of 16 different antigen tests determined that they correctly identified COVID 19 infection in an average of 72 of people with symptoms compared to 58 of people without symptoms 63 needs update Tests were most accurate 78 when used in the first week after symptoms first developed likely because people have the most virus in their system in the first days after they are infected 63 While some scientists doubt whether an antigen test can be useful against COVID 19 62 others have argued that antigen tests are highly sensitive when viral load is high and people are contagious making them suitable for public health screening 64 65 Routine antigen tests can quickly identify when asymptomatic people are contagious while follow up PCR can be used if confirmatory diagnosis is needed 66 Antibody tests nbsp nbsp Left Automated analyzer for immunoassays used for example to find SARS CoV 2 antibodies Right Example of quantitative results for SARS CoV 2 antibody test The body responds to a viral infection by producing antibodies that help neutralize the virus 67 Blood tests also called serology tests or serology immunoassays 3 can detect the presence of such antibodies 68 Antibody tests can be used to assess what fraction of a population has once been infected which can then be used to calculate the disease s mortality rate 5 They can also be used to determine how much antibody is contained in a unit of convalescent plasma for COVID 19 treatment or to verify if a given vaccine generates an adequate immune response 69 SARS CoV 2 antibodies potency and protective period have not been established 5 70 Therefore a positive antibody test may not imply immunity to a future infection Further whether mild or asymptomatic infections produce sufficient antibodies for a test to detect has not been established 71 Antibodies for some diseases persist in the bloodstream for many years while others fade away 56 The most notable antibodies are IgM and IgG IgM antibodies are generally detectable several days after initial infection although levels over the course of infection and beyond are not well characterized 72 IgG antibodies generally become detectable 10 14 days after infection and normally peak around 28 days after infection 73 74 This pattern of antibody development seen with other infections often does not apply to SARS CoV 2 however with IgM sometimes occurring after IgG together with IgG or not occurring at all 75 Generally however median IgM detection occurs 5 days after symptom onset whereas IgG is detected a median 14 days after symptom onset 76 IgG levels significantly decline after two or three months 77 Genetic tests verify infection earlier than antibody tests Only 30 of those with a positive genetic test produced a positive antibody test on day 7 of their infection 71 Antibody Test Types Rapid diagnostic test RDT RDTs typically use a small portable positive negative lateral flow assay that can be executed at point of care RDTs may process blood samples saliva samples or nasal swab fluids RDTs produce colored lines to indicate positive or negative results 78 Enzyme linked immunosorbent assay ELISA ELISAs can be qualitative or quantitative and generally require a lab These tests usually use whole blood plasma or serum samples A plate is coated with a viral protein such as a SARS CoV 2 spike protein Samples are incubated with the protein allowing any antibodies to bind to it The antibody protein complex can then be detected with another wash of antibodies that produce a color fluorescent readout 78 Neutralization assay Neutralization assays assess whether sample antibodies prevent viral infection in test cells 67 These tests sample blood plasma or serum The test cultures cells that allow viral reproduction e g Vero E6 cells By varying antibody concentrations researchers can visualize and quantify how many test antibodies block virus replication 78 Chemiluminescent immunoassay Chemiluminescent immunoassays are quantitative lab tests They sample blood plasma or serum Samples are mixed with a known viral protein buffer reagents and specific enzyme labeled antibodies The result is luminescent A chemiluminescent microparticle immunoassay uses magnetic protein coated microparticles Antibodies react to the viral protein forming a complex Secondary enzyme labeled antibodies are added and bind to these complexes The resulting chemical reaction produces light The radiance is used to calculate the number of antibodies This test can identify multiple types of antibodies including IgG IgM and IgA 78 Neutralizing vis a vis binding antibodies Most if not all large scale COVID 19 antibody testing looks for binding antibodies only and does not measure the more important neutralizing antibodies NAb 79 80 81 A NAb is an antibody that neutralizes the infectivity of a virus particle by blocking its attachment to or entry into a susceptible cell enveloped viruses like e g SARS CoV 2 are neutralized by the blocking of steps in the replicative cycle up to and including membrane fusion 82 67 A non neutralizing antibody either does not bind to the crucial structures on the virus surface or binds but leaves the virus particle infectious the antibody may still contribute to the destruction of virus particles or infected cells by the immune system 83 67 It may even enhance infectivity by interacting with receptors on macrophages 84 Since most COVID 19 antibody tests return a positive result if they find only binding antibodies these tests cannot indicate that the subject has generated protective NAbs that protect against re infection 80 81 It is expected that binding antibodies imply the presence of NAbs 81 and for many viral diseases total antibody responses correlate somewhat with NAb responses 85 but this is not established for COVID 19 A study of 175 recovered patients in China who experienced mild symptoms reported that 10 individuals had no detectable NAbs at discharge or thereafter How these patients recovered without the help of NAbs and whether they were at risk of re infection was not addressed 80 An additional source of uncertainty is that even if NAbs are present viruses such as HIV can evade NAb responses 79 Studies have indicated that NAbs to the original SARS virus the predecessor to the current SARS CoV 2 can remain active for two years 86 and are gone after six years 87 Nevertheless memory cells including memory B cells and memory T cells 88 can last much longer and may have the ability to reduce reinfection severity 87 nbsp A point of care test in Peru A blood droplet is collected by a pipette nbsp Blood from pipette is then placed onto a COVID 19 rapid diagnostic test device nbsp The rapid diagnostic test shows reactions of IgG and IgM antibodies The left tray shows a negative result and the right positive nbsp Home test with a positive result The C is the control the T is the test Other tests Sniff tests Sudden loss of smell can be used to screen people on a daily basis for COVID 19 A study by the National Institutes of Health showed that those infected with SARS CoV 2 could not smell a 25 mixture of ethanol and water 89 Because various conditions can lead to the loss of the sense of smell a sniff test would not be definitive but indicate the need for a PCR test Because the loss of the sense of smell shows up before other symptoms there has been a call for widespread sniff testing 90 Health care bureaucracies have generally ignored sniff tests even though they are quick easy and capable of being self administered daily This has led some medical journals to write editorials supporting the adoption of sniff testing 91 Imaging Typical visible features on CT initially include bilateral multilobar ground glass opacities with a peripheral or posterior distribution 92 COVID 19 can be identified with higher precision using CT than with RT PCR 93 Subpleural dominance crazy paving and consolidation may develop as the disease evolves 92 94 Chest CT scans and chest x rays are not recommended for diagnosing COVID 19 Radiologic findings in COVID 19 lack specificity 92 95 Chest X rays computed tomography scans and ultrasounds are all ways the coronavirus disease can be detected A chest x ray is a portable lightweight machine This machine is typically more available than polymerase chain reaction and computerized tomography scans it only takes approximately 15 seconds per patient 96 This makes chest x ray readily accessible and inexpensive It also has quick turnaround time and can be crucial to the clinical equipment in the detection of coronavirus disease 97 Computerized tomography scans involve looking at 3D images from various angles This is not as available as chest x ray but still only takes about 15 minutes per patient 96 Computerized tomography has been a known routine scanning for pneumonia diagnosis therefore can also be used to diagnose coronavirus disease Computerized tomography scans may help with ongoing illness monitoring throughout treatment Patients who had low grade symptoms and high body temperatures revealed significant lung indications on their chest computed tomography scans They emphasized how important chest computerized tomography scans are for determining how serious the coronavirus disease infection is 98 Ultrasound can be another tool to detect coronavirus disease An ultrasound is a type of imaging exam that produces images using sound waves Unlike computerized tomography scans and x rays ultrasound does not use radiation Moreover it is inexpensive simple to use repeatable and has several additional advantages Using a hand held mobile machine ultrasound examinations can be performed in a variety of healthcare settings 99 There are some downsides to using imaging however The equipment needed for computed tomography scans is not available in most hospitals making it not as effective as some other tools used for detection of the coronavirus disease 96 One of the difficult tasks in a pandemic is manually inspecting each report which takes numerous radiology professionals and time 100 There were several problems with early studies of using chest computerized tomography scans for diagnosing coronavirus Some of these problems included the disease severity characters being different in severe and hospitalized cases The criteria for doing a chest computerized tomography scan were not defined There was also no characterization of positive chest computerized tomography scans results The computerized tomography scans findings were not the same as positive computerized tomography scans findings of coronavirus 99 In a typical clinical setting chest imaging is not advised for routine screening of COVID 19 Patients with asymptomatic to mild symptoms are not recommended to be tested via chest computerized tomography scans However it is still crucial to use particularly when determining complications or disease progression Chest imaging also is not always the first route to take with patients who have high risk factors for COVID High risk patients that had mild symptoms chest imaging findings were limited Although a computerized tomography scan is a strong tool in the diagnosis of COVID 19 it is insufficient to identify COVID 19 alone due to the poor specificity and the difficulties that radiologists may experience in distinguishing COVID 19 from other viral pneumonia on chest computerized tomography scans 98 Serology CoLab score tests The standard blood test quick scan taken at the emergency room measures different values By use of the blood quick scan the CoLab score is calculated with a developed algorithm based on how the coronavirus causes changes in the blood The software is intended for use in emergency rooms to quickly rule out the presence of the disease in incoming patients A not negative result is followed by a PCR polymerase chain reaction or LAMP loop mediated isothermal amplification test 101 Breath tests The breath test by a Coronavirus breathalyzer is a pre screening test for people who have no or mild symptoms of COVID 19 A not negative result is followed by a PCR or LAMP test citation needed Animals In May 2021 Reuters reported that Dutch researchers at Wageningen University had shown that trained bees could detect the virus in infected samples in seconds and this could benefit countries where test facilities are in short supply 102 A two month study by the Necker Cochin hospital Paris in conjunction with the French national veterinary school reported in May 2021 that dogs were more reliable than current lateral flow tests 103 Researchers in Paris in March 2022 reported in a preprint not yet peer reviewed that trained dogs were very effective for rapidly detecting the presence of SARS Cov2 in people whether displaying symptoms or not The dogs were presented with sweat samples to smell from 335 people of whom 78 with symptoms and 31 without tested positive by PCR The dogs detected 97 of the symptomatic and 100 of the asymptomatic infections They were 91 accurate at identifying volunteers who were not infected and 94 accurate at ruling out the infection in people without symptoms The authors said Canine testing is non invasive and provides immediate and reliable results Further studies will be focused on direct sniffing by dogs to evaluate sniffer dogs for mass pre test in airports harbors railways stations cultural activities or sporting events 104 105 Functional assays Tollotest is a molecular test that detects the activity of a SARS CoV2 protease which is a biomarker for active infection 106 HistoryMain article Development of COVID 19 tests nbsp Timeline of total number of tests in different countries 107 In January 2020 scientists from China published the first genetic sequences of SARS CoV 2 via virological org 108 a hub for prepublication data designed to assist with public health activities and research 109 Researchers around the world used that data to build molecular tests for the virus Antigen and antibody based tests were developed later citation needed Even once the first tests were created the supply was limited As a result no countries had reliable data on the prevalence of the virus early in the pandemic 110 The WHO and other experts called for ramping up testing as the best way to slow the spread of the virus 111 112 Shortages of reagent and other testing supplies became a bottleneck for mass testing in the EU the UK and the US 113 114 115 Early tests also encountered problems with reliability 116 117 Testing protocolsDrive through testing In drive through testing the person undergoing testing remains in a vehicle while a healthcare professional approaches the vehicle and obtains a sample all while taking appropriate precautions such as wearing personal protective equipment PPE 118 119 Drive through centers helped South Korea accelerate its testing program 120 Home collection nbsp A Randox PCR home test kit in the UK showing the swab and multi layer packaging to deliver it to the lab nbsp A USPS package containing COVID 19 tests from the fifth round of free US distributions in the fall of 2023 with instructions regarding FDA extensions of test expiration dates In Hong Kong test subjects can stay home and receive a specimen tube They spit into it return it and later get the result 121 Additionally by the fall of 2023 the United States had conducted six rounds of mailing free at home COVID 19 tests to households nationwide The rapid antigen tests while less accurate than PCR tests did not require mailing the tests back to labs for analysis 122 123 Pooled testing See also List of countries implementing pool testing strategy against COVID 19 Pooled testing can improve turnaround time by combining a number of samples to be tested together If the pool result is negative all samples are negative If the test result is positive samples will need to be individually tested 69 In Israel researchers at Technion and Rambam Hospital developed a method for testing samples from 64 patients simultaneously by pooling the samples and only testing further if the combined sample was positive 124 125 126 Pool testing was then adopted in Israel Germany Ghana 127 128 129 South Korea 130 Nebraska 131 China 132 and the Indian states of Uttar Pradesh 133 West Bengal 134 Punjab 135 Chhattisgarh 136 and Maharashtra 137 Open source multiplexed designs released by Origami Assays can test as many as 1122 patient samples using only 93 assays 138 These balanced designs can be run in small laboratories without robotic liquid handlers Multi tiered testing One study proposed a rapid immune response assay as a screening test with a confirmatory nucleic acid test for diagnosis followed by a rapid antibody test to determine course of action and assess population exposure herd immunity 139 Required volume Required testing levels are a function of disease spread The more the cases the more tests are needed to manage the outbreak COVID 19 tends to grow exponentially at the beginning of an outbreak meaning that the number of required tests initially also grows exponentially If properly targeted testing grows more rapidly than cases it can be contained citation needed WHO recommends increasing testing until fewer than 10 are positive in any given jurisdiction 140 United States nbsp Number of tests done per day in the US as of April 2020 update Blue CDC lab Orange Public health lab Gray Data incomplete due to reporting lag Not shown Testing at private labs total exceeded 100 000 per day by 27 March 141 Economist Paul Romer reported that the US has the technical capacity to scale up to 20 million tests per day which is his estimate of the scale needed to fully remobilize the economy 142 The Edmond J Safra Center for Ethics estimated on 4 April 2020 that this capacity could be available by late July 2020 143 Romer pointed to single molecule real time sequencing equipment from Pacific Biosciences 142 144 and to the Ion Torrent Next Generation Sequencing equipment from ThermoFisher Scientific 142 145 According to Romer Recent research papers suggest that any one of these has the potential to scale up to millions of tests per day This plan requires removing regulatory hurdles Romer estimated that 100 billion would cover the costs 142 Romer also claimed that high test accuracy is not required if tests are administered frequently enough He ran model simulations in which 7 of the population is tested every day using a test with a 20 false negative rate and a 1 false positive rate The average person would be tested roughly every two weeks Those who tested positive would go into quarantine Romer s simulation indicated that the fraction of the population that is infected at any given time known as the attack rate peaks reaches roughly 8 in about thirty days before gradually declining in most runs reaching zero at 500 days with cumulative prevalence remaining below 20 146 Snapshot mass testing A study found that despite possibly suboptimal implementation the snapshot mass testing approach conducted by Slovakia by which 80 of its population was tested for COVID 19 within a weekend at the end of October 2020 was thought highly efficacious decreasing observed prevalence by 58 within one week and by 70 compared to a hypothetical scenario of no snapshot mass testing 147 148 The significant reduction resulted from a set of complementary lockdown and quarantine measures whereby citizens who tested positive were quarantined synchronously the weeks afterwards 149 The country increased other countermeasures at the same time so the inference was questionable In the following months Slovakia s COVID 19 death rate per population increased to among the highest in the world Research on mass testing suggests that people who test negative think it is safe to travel and come in contact with infected people In the U S the tracing system was overwhelmed On 70 percent of days there were more cases than tracers had time to contact and people contacted were often uncooperative 150 Surveillance and screening of populations See also Pandemic prevention Surveillance and mapping As of August 2020 the WHO recognizes wastewater surveillance of SARS CoV 2 as a potentially useful source of information on the prevalence and temporal trends of COVID 19 in communities while highlighting that gaps in research such as viral shedding characteristics should be addressed 151 Such aggregative testing may have detected early cases 152 Studies show that wastewater based epidemiology has the potential for an early warning system and monitoring for COVID 19 infections 153 154 155 156 157 This may prove particularly useful once large shares of regional populations are vaccinated or recovered and do not need to conduct rapid tests while in some cases being infectious nevertheless 158 Available tests nbsp A temporary drive in testing site for COVID 19 set up with tents in a parking lot Countries around the world developed tests independently and in partnership with others Nucleic acid tests Tests are available that look for viral DNA using either polymerase chain reaction PCR or loop mediated isothermal amplification LAMP technology Tests developed in China France Germany Hong Kong Japan the United Kingdom and the US targeted different parts of the viral genome WHO adopted the German system for manufacturing kits sent to low income countries without the resources to develop their own citation needed PowerChek Coronavirus looks for the E gene shared by all beta coronaviruses and the RdRp gene specific to SARS CoV 2 159 nbsp US President Donald Trump displays a COVID 19 testing kit from Abbott Laboratories in March 2020 nbsp Nucleic acid testing conducted using an Abbott Laboratories ID Now device Abbott Laboratories ID Now nucleic acid test uses isothermal amplification technology 160 The assay amplifies a unique region of the virus s RdRp gene the resulting copies are then detected with fluorescently labeled molecular beacons 161 The test kit uses the company s toaster size ID Now device which is widely deployed in the US 162 The device can be used in laboratories or in point of care settings and provides results in 13 minutes or less 161 Primerdesign offers its Genesig Real Time PCR test system Roche Molecular Systems offers the Cobas 6800 8800 systems they are offered among others by the United Nations citation needed Antigen tests Main article COVID 19 rapid antigen test nbsp Innova SARS CoV 2 Antigen Rapid Qualitative Lateral Flow Test kit showing a negative result This device has been subject to accuracy concerns and a recall in the United States Antigen tests are readily available worldwide and have been approved by several health regulators Quidel s Sofia 2 SARS Antigen FIA 66 163 is a lateral flow test that uses monoclonal antibodies to detect the virus s nucleocapsid N protein 164 The result is read out by the company s Sofia 2 device using immunofluorescence 164 The test is simpler and cheaper but less accurate than nucleic acid tests It can be deployed in laboratories or at point of care and gives results in 15 minutes 163 A false negative result occurs if the sample s antigen level is positive but below the test s detection limit requiring confirmation with a nucleic acid test 164 The Innova SARS CoV 2 Antigen Rapid Qualitative Test was never approved for use in the United States but was being sold by the company anyway The FDA inspected Innova facilities in California in March and April 2021 and found inadequate quality assurance of tests manufactured in China 165 On 23 April 2021 the company issued a recall The FDA warned consumers to return or destroy the devices because the rate of false positives and false negatives found in clinical trials were higher than the rate claimed by the packaging 166 Over 1 billion tests from the company have been distributed in the UK with 3 billion in funding as part of Operation Moonshot and the MHRK has authorized exceptional use until at least 28 August 2021 165 Concerned experts pointed out that accuracy dropped significantly when screening was conducted by the public instead of by a medical professional and that the test was not designed to screen asymptomatic people 165 A 2020 study found 79 of positive cases were found when used by laboratory scientists but only 58 when used by the general public and 40 when used for city wide screening in Liverpool 167 Serology antibody tests Antibodies are usually detectable 14 days after the onset of the infection Multiple jurisdictions survey their populations using these tests 168 169 The test requires a blood sample Private US labs including Quest Diagnostics and LabCorp offer antibody testing upon request 170 Certain antibody tests are available in several European countries and also in the US 171 172 Roche offers a selective ELISA serology test 173 A summary review in BMJ has noted that while some serological tests might be cheaper and easier to implement at the point of care than RT PCR and such testing can identify previously infected individuals caution is warranted using serological tests for epidemiological surveillance The review called for higher quality studies assessing accuracy with reference to a standard of RT PCR performed on at least two consecutive specimens and when feasible includ ing viral cultures 174 175 CEBM researchers have called for in hospital case definition to record CT lung findings and associated blood tests 176 and for the WHO to produce a protocol to standardise the use and interpretation of PCR with continuous re calibration 177 AccuracyThe location of sample collection impact on sensitivity for COVID 19 in 205 Wuhan patients 178 Samples source Positive rate Bronchoalveolar lavage fluid specimens 93 14 15 Sputum 72 75 104 Nasal swabs 63 5 8 Fibrobronchoscope brush biopsy 46 6 13 Pharyngeal swabs 32 126 398 Feces 29 44 153 Blood 1 3 307 Accuracy is measured in terms of specificity and selectivity Test errors can be false positives the test is positive but the virus is not present or false negatives the test is negative but the virus is present 179 In a study of over 900 000 rapid antigen tests false positives were found to occur at a rate of 0 05 or 1 in 2000 180 Sensitivity and specificity Main article Sensitivity and specificity Sensitivity indicates whether the test accurately identifies whether the virus is present Each test requires a minimum level of viral load in order to produce a positive result A 90 sensitive test will correctly identify 90 of infections missing the other 10 a false negative Even relatively high sensitivity rates can produce high rates of false negatives in populations with low incidence rates 179 In a diagnostic test sensitivity is a measure of how well a test can identify true positives and specificity is a measure of how well a test can identify true negatives For all testing both diagnostic and screening there is usually a trade off between sensitivity and specificity such that higher sensitivities will mean lower specificities and vice versa nbsp Sensitivity and SpecificityA 90 specific test will correctly identify 90 of those who are uninfected leaving 10 with a false positive result citation needed Low specificity tests have a low positive predictive value PPV when prevalence is low For example suppose incidence is 5 Testing 100 people at random using a test that has a specificity of 95 would yield on average 5 people who are actually negative who would incorrectly test positive Since 5 of the subjects actually are positive another five would also test positive correctly totaling 10 positive results Thus the PPV is 50 181 an outcome no different from a coin toss In this situation assuming that the result of a second test is independent of the first test retesting those with a first positive result increases the PPV to 94 5 meaning that only 4 5 of the second tests would return the incorrect result on average less than 1 incorrect result 182 Causes of test error The time course of infection affects the accuracy of some tests Samples may be collected before the virus has had a chance to establish itself or after the body has begun to eliminate it A May 2020 review of PCR RT testing found that the median probability of a false negative result decreased from 100 on day 1 to 67 on day 4 On the day of symptom onset the probability was 38 which decreased to 20 3 days later 183 needs update PCR based test nbsp Detection of SARS CoV 2 by nasal swab over six weeks in patients who experienced mild to moderate illness RT PCR is the most commonly used diagnostic test 184 PCR tests by nasopharyngeal swab have a sensitivity of 73 but systematic analysis of specificity has not been determined due to the lack of PCR studies with a control group 185 In one study sensitivity was highest at week one 100 followed by 89 3 66 1 32 1 5 4 and zero by week six since symptom onset 186 failed verification 187 Sensitivity is also a function of the number of PCR cycles as well as time and temperature between sample collection and analysis 188 A cycle threshold of 20 cycles would be adequate to detect SARS Cov 2 in a highly infective person 188 Cycle thresholds above 34 are increasingly likely to give false positives outside of high biosafety level facilities 188 On July 16 2020 Dr Anthony Fauci of the US CDC indicated that positive results obtained from RT PCR tests run at more than 35 cycles were almost always just dead nucleotides 189 On August 29 2020 the New York Times reported that In three sets of testing data that include cycle thresholds compiled by officials in Massachusetts New York and Nevada most tests set the limit at 40 cycles a few at 37 and that the CDC was examining the use of cycle threshold measures for policy decisions 190 On July 21 2021 the CDC in their Real Time RT PCR Diagnostic Pan Instructions for Use indicated tests results should be determined at 40 cycles 191 A Dutch CDC led laboratory investigation compared 7 PCR kits 192 Test kits made by BGI R Biopharm AG BGI KH Medical and Seegene showed high sensitivity 193 High sensitivity kits are recommended to assess people without symptoms while lower sensitivity tests are adequate when diagnosing symptomatic patients 192 The University of Oxford s Centre for Evidence Based Medicine CEBM has pointed to mounting evidence 194 195 that a good proportion of new mild cases and people re testing positives via RT PCR after quarantine or discharge from hospital are not infectious but are simply clearing harmless virus particles which their immune system has efficiently dealt with and have called for an international effort to standardize and periodically calibrate testing 176 On 7 September the UK government issued guidance for procedures to be implemented in laboratories to provide assurance of positive SARS CoV 2 RNA results during periods of low prevalence when there is a reduction in the predictive value of positive test results 196 On 4 January 2021 the US FDA issued an alert about the risk of false results particularly false negative results with the Curative SARS Cov 2 Assay real time RT PCR test 49 Isothermal nucleic amplification test One study reported that the ID Now COVID 19 test showed sensitivity of 85 2 Abbott responded that the issue could have been caused by analysis delays 197 Another study rejected the test in their clinical setting because of this low sensitivity 198 Confirmatory testingThe WHO recommends countries that do not have testing capacity and national laboratories with limited experience on COVID 19 send their first five positives and the first ten negative COVID 19 samples to one of the 16 WHO reference laboratories for confirmatory testing 199 200 Out of the sixteen reference laboratories seven are in Asia five in Europe two in Africa one in North America and one in Australia 201 National or regional responsesIceland Iceland managed the pandemic with aggressive contact tracing inbound travel restrictions testing and quarantining but with less aggressive lock downs 202 India Main article COVID 19 pandemic in India Testing and countermeasures Italy Researchers tested the entire population of Vo the site of Italy s first COVID 19 death They tested about 3 400 people twice at an interval of ten days About half the people testing positive had no symptoms All discovered cases were quarantined Along with restricting travel to the commune new infections were eliminated 203 Japan Unlike other Asian countries Japan did not experience a pandemic of SARS or MERS so the country s PCR testing system was not well developed 204 205 Japan preferentially tested patients with severe illness and their close contacts at the beginning Japan s Novel Coronavirus Expert Meeting chose cluster measures to identify infections clusters 204 205 The Expert Meeting analyzed the outbreak from Wuhan and identified conditions leading to clusters closed spaces crowded spaces and close contact and asked people to avoid them 205 206 In January contact tracers took action shortly after the first infection was found Only administrative tests were carried out at first until insurance began covering PCR tests on 6 March Private companies began to test and the test system gradually expanded 204 207 On 3 April those with positive tests were legally permitted to recuperate at home or in a hotel if they had asymptomatic or mild illness ending the hospital bed shortage 208 The first wave from China was contained 209 but a second wave caused by returnees from Europe and the US in mid March led to spreading infection in April 205 On 7 April Japan declared a state of emergency less strict than a lockdown because it did not block cities or restrict outings 205 208 210 On 13 May antigen test kits became covered by insurance and were combined with a PCR test for diagnosis 211 212 Japan s PCR test count per capita remained far smaller than in some other countries even though its positive test rate was lower Excess mortality was observed in March 206 failed verification 210 failed verification 213 The Expert Meeting stated The Japanese health care system originally carries out pneumonia surveillance allowing it to detect most of the severely ill patients who develop pneumonia There are a large number of CT scanners in Japan and they have spread to small hospitals all over the country so pneumonia patients are rarely missed In that sense it meets the same standards as other countries that mainly carry out PCR tests 206 213 The group recommended using CT scans data and doctor s findings for diagnosis 214 215 On the Diamond Princess cruise ship many people who initially tested negative later tested positive Half of coronavirus positives there who remained mild or asymptomatic had pneumonia findings on CT scans and their CT image showed a frosted glass shadow that is characteristic of infection 214 216 As of 18 July Japan s daily PCR testing capacity was about 32 000 more than three times the 10 000 cases as of April When the antigen test is added to it the number is about 58 000 The number of tests per 1 000 people in the United States is about 27 times that of Japan the UK is 20 times Italy is 8 times and South Korea is twice as of 26 July 217 218 219 The number of those infected with coronavirus and inpatients has increased in July but the number of serious cases has not increased This is thought to be due to the proper testing of those infected in July compared to those in April In April the number of tests could not catch up with the increase in the number of infected people and the test standards were strict so the test positive rate exceeded 30 at the peak It means that there were quite a few cases where those infected were not PCR tested It is thought that the severe case was preferentially tested though there were a lot of mild cases and asymptomatic carriers mainly in the young during the first wave In other words it became possible to grasp the actual situation of infection much better than before by strengthening the testing system 220 At the end of July accommodation facilities for mild and asymptomatic carriers became full and the authorities requested hospitals to prepare beds for the mild However it became difficult to treat patients with other illnesses and to maintain the ICU system including the staff due to the occupation of hospital beds by patients with mild symptoms 221 222 223 Russia On 27 April 2020 Russia tested 3 million people and had 183 000 positive results 224 On 28 April Anna Popova head of Federal Service for Surveillance in Healthcare Roszdravnadzor stated that 506 laboratories were testing that 45 of those who tested positive had no symptoms that 5 of patients had a severe form and 40 of infections were from family members Illness improved from six days to one day after symptoms appeared Antibody testing was carried out on 3 200 Moscow doctors finding 20 immunity 225 Singapore With contact tracing inbound travel restrictions testing and quarantining Singapore arrested the initial spread without complete lockdown 226 Slovakia In late October 2020 Slovakia tested 3 62 million people in a weekend from a population of 5 4m representing 67 of the total or 82 of the adult population 38 359 tested positive representing 1 06 of those tested The government considered the mass test would significantly assist in controlling the virus and avoid a lockdown and may repeat the exercise at a later date 227 South Korea South Korea s broad testing approach helped reduce spread Testing capacity largely in private sector labs was built up over several years by the South Korean government in the early 2000s 228 The government exploited the resident registration number RRN system Authorities mobilized young men who were eligible for military service as social service agents security and public health doctors Public health doctors were mainly dispatched to public health centers and life treatment centers where mildly ill patients were accommodated They performed PCR tests and managed mild patients Social service agents worked in pharmacies to fill staff shortages Korea s 10k PCR tests per million residents was the world s highest as of 13 April rising to 20k by mid June Twenty seven Korean companies exported test kits worth 48 6 million in March and were asked to provide test kits or humanitarian assistance by more than 120 countries Korean authorities set up a treatment center to isolate and manage patients with asymptomatic and minor illnesses in one facility in order to vacate hospital beds for the more severely ill Centers were sited mainly at national facilities and corporate training centers The failure of Korea s MERS quarantine in May 2015 left Korea more prepared for COVID 19 than countries that did not face that pandemic Then President Park Geun hye allowed Korean CDC approved private sector testing for infectious diseases in 2016 Korea already had a system for isolating testing and treating infectious disease patients separately from others Patients with respiratory illness but no epidemiological relevance were treated at the National Hospital and those with epidemiological relevance were treated at selected clinics 229 230 231 232 233 234 235 236 237 Korea established a large scale drive through walk through test testing program However the most common method was mobile examination In Daegu City 54 of samples were collected by 23 March in home or hospital Collecting samples door to door of avoided the risk of travel by possibly infected patients but required additional staff Korea solved the problem by drafting more than 2 700 public insurance doctors 229 233 232 The government disclosed personal information to the public via KCDC without patient consent The authorities used digital surveillance to trace possible spread 230 233 234 236 237 238 239 240 241 242 excessive citations Taiwan Health insurance IDs and national identification card numbers were used to trace contacts 243 244 245 246 United Arab Emirates In January 2021 the COVID 19 testing results of the UAE came under scrutiny as Denmark suspended the Emirati flights for five days The European nation said that it barred the flights from the UAE due to growing suspicion of irregularities in the testing process being followed in the Gulf nation Denmark s Minister of Transport Benny Engelbrecht said that they were taking time to ensure that the negative tests of travelers from the Emirates were a real screening carried out appropriately 247 United States Main article COVID 19 testing in the United States New York State New York State s control measures consisted of PCR tests stay at home measures and strengthening the healthcare system On 29 February before its first case the state allowed testing at the Wordsworth Center They managed to convince the CDC to approve tests at state laboratories and the FDA to approve a test kit As of 13 March the state was conducting more than 1 000 daily tests growing to 10 000 day on 19 March In April the number exceeded 20 000 Many people queued at hospitals to get tested On 21 March New York City health officials directed medical providers to test only those entering the hospital for lack of PPE 236 248 249 250 251 excessive citations USS Theodore Roosevelt Main article COVID 19 pandemic on USS Theodore Roosevelt Following an outbreak 94 of the 4 800 aircraft carrier crew were tested Roughly 60 percent of the 600 plus sailors who tested positive were asymptomatic 252 Five infected sailors who completed quarantine subsequently developed flu like symptoms and again tested positive 253 Nevada In 2020 Nevada received a donation of 250 000 Covid testing kits which were a product of China s leading genetics company BGI Group A UAE based firm owned by Tahnoun bin Zayed Al Nahyan Group 42 partnered with the BGI Group to supply the testing kits to Nevada However the US Department of Homeland Security and the State Department raised a warning for Nevada hospitals to not use the Chinese made testing kits as there were concerns around the involvement of the Chinese government test accuracy and privacy of the patients 254 Delayed testing A shortage of trained medical laboratory scientists assay reagents analyzers transport medium and PPE coupled with high demand had limited initially limited the availability of testing and led to significantly increased turnaround times citation needed Testing statistics by countryTesting strategies vary by country and over time 255 with some countries testing very widely 8 while others have at times focused narrowly on only testing the seriously ill 6 The country that tests only people showing symptoms will have a higher figure for Confirmed tested than the country that also tests others 256 If two countries are alike in every respect including which people they test the one that tests more people will have a higher Confirmed population Studies have also found that countries that test more relative to the number of deaths have lower estimated case fatality rates 9 and younger age distributions of cases 11 vteCOVID 19 testing statistics by country Country or region Date a Tested Units b Confirmed cases Confirmed tested Tested population Confirmed population Ref nbsp Afghanistan 17 Dec 2020 154 767 samples 49 621 32 1 0 40 0 13 257 nbsp Albania 18 Feb 2021 428 654 samples 96 838 22 6 15 0 3 4 258 nbsp Algeria 2 Nov 2020 230 553 samples 58 574 25 4 0 53 0 13 259 260 nbsp Andorra 23 Feb 2022 300 307 samples 37 958 12 6 387 49 0 261 nbsp Angola 2 Feb 2021 399 228 samples 20 981 5 3 1 3 0 067 262 nbsp Antigua and Barbuda 6 Mar 2021 15 268 samples 832 5 4 15 9 0 86 263 nbsp Argentina 16 Apr 2022 35 716 069 samples 9 060 495 25 4 78 3 20 0 264 nbsp Armenia 29 May 2022 3 099 602 samples 422 963 13 6 105 14 3 265 nbsp Australia 9 Sep 2022 78 548 492 samples 10 112 229 12 9 313 40 3 266 nbsp Austria 1 Feb 2023 205 817 752 samples 5 789 991 2 8 2 312 65 0 267 nbsp Azerbaijan 11 May 2022 6 838 458 samples 792 638 11 6 69 1 8 0 268 nbsp Bahamas 28 Nov 2022 259 366 samples 37 483 14 5 67 3 9 7 269 nbsp Bahrain 3 Dec 2022 10 578 766 samples 696 614 6 6 674 44 4 270 nbsp Bangladesh 24 Jul 2021 7 417 714 samples 1 151 644 15 5 4 5 0 70 271 nbsp Barbados 14 Oct 2022 770 100 samples 103 014 13 4 268 35 9 272 nbsp Belarus 9 May 2022 13 217 569 samples 982 809 7 4 139 10 4 273 nbsp Belgium 24 Jan 2023 36 548 544 samples 4 691 499 12 8 317 40 7 274 nbsp Belize 8 Jun 2022 572 900 samples 60 694 10 6 140 14 9 275 276 nbsp Benin 4 May 2021 595 112 samples 7 884 1 3 5 1 0 067 277 nbsp Bhutan 28 Feb 2022 1 736 168 samples 12 702 0 73 234 1 71 278 nbsp Bolivia 5 Jun 2022 4 358 669 cases 910 228 20 9 38 1 8 0 279 nbsp Bosnia and Herzegovina 27 Sep 2022 1 872 934 samples 399 887 21 4 54 7 11 7 280 nbsp Botswana 11 Jan 2022 2 026 898 232 432 11 5 89 9 10 3 281 282 nbsp Brazil 19 Feb 2021 23 561 497 samples 10 081 676 42 8 11 2 4 8 283 284 nbsp Brunei 2 Aug 2021 153 804 samples 338 0 22 33 5 0 074 285 nbsp Bulgaria 2 Feb 2023 10 993 239 samples 1 295 524 11 8 158 18 6 286 nbsp Burkina Faso 4 Mar 2021 158 777 samples 12 123 7 6 0 76 0 058 259 287 nbsp Burundi 5 Jan 2021 90 019 884 0 98 0 76 0 0074 288 nbsp Cambodia 1 Aug 2021 1 812 706 77 914 4 3 11 2 0 48 289 nbsp Cameroon 18 Feb 2021 942 685 samples 32 681 3 5 3 6 0 12 259 nbsp Canada 26 Nov 2022 66 343 123 samples 4 423 053 6 7 175 11 7 290 nbsp Chad 2 Mar 2021 99 027 samples 4 020 4 1 0 72 0 029 259 291 nbsp Chile 1 Feb 2023 48 154 268 samples 5 123 007 10 6 252 26 9 292 nbsp China c 31 Jul 2020 160 000 000 cases 87 655 0 055 11 1 0 0061 293 294 nbsp Colombia 24 Nov 2022 36 875 818 samples 6 314 769 17 1 76 4 13 1 295 296 nbsp Costa Rica 2 Nov 2021 2 575 363 samples 561 054 21 8 51 5 11 2 297 nbsp Croatia 2 Feb 2023 5 481 285 cases 1 267 798 23 1 134 31 1 298 nbsp Cuba 2 Feb 2023 14 301 394 samples 1 112 470 7 8 126 9 8 299 300 nbsp Cyprus d 29 Jan 2023 27 820 163 samples 644 160 2 3 3 223 74 4 301 nbsp Czechia 1 Feb 2023 22 544 928 samples 4 590 529 20 4 211 42 9 302 nbsp Denmark e 31 Jan 2023 67 682 707 samples 3 399 947 5 0 1 162 58 4 303 304 nbsp Djibouti 28 Apr 2022 305 941 15 631 5 1 33 2 1 7 305 nbsp Dominica 20 Jun 2022 209 803 cases 14 821 7 1 293 20 7 306 nbsp Dominican Republic 22 Jul 2022 3 574 665 samples 626 030 17 5 32 9 5 8 307 nbsp DR Congo 28 Feb 2021 124 838 25 961 20 8 0 14 0 029 259 308 nbsp Ecuador 23 Jul 2021 1 627 189 samples 480 720 29 5 9 5 2 8 309 nbsp Egypt 23 Jul 2021 3 137 519 samples 283 947 9 1 3 1 0 28 259 310 nbsp El Salvador 18 Mar 2022 1 847 861 samples 161 052 8 7 28 5 2 5 311 nbsp Equatorial Guinea 30 Jan 2023 403 773 17 113 4 2 30 8 1 3 312 nbsp Estonia 31 Jan 2023 3 637 908 samples 613 954 16 9 274 46 2 313 nbsp Eswatini 8 Dec 2021 415 110 49 253 11 9 36 5 4 3 314 nbsp Ethiopia 24 Jun 2021 2 981 185 samples 278 446 9 3 2 6 0 24 315 nbsp Faroe Islands 27 Feb 2022 774 000 samples 34 237 4 4 1 493 65 7 316 nbsp Fiji 2 Jan 2023 667 953 samples 68 848 10 3 74 5 7 7 317 nbsp Finland 14 Jan 2022 9 042 453 samples 371 135 4 1 163 6 7 318 nbsp France f g 15 May 2022 272 417 258 samples 29 183 646 10 7 417 44 7 319 nbsp Gabon 23 Jul 2021 958 807 samples 25 325 2 6 3 1 0 082 320 nbsp Gambia 15 Feb 2021 43 217 samples 4 469 10 3 2 0 0 21 321 nbsp Georgia h 3 Nov 2021 4 888 787 samples 732 965 15 0 132 19 7 322 nbsp Germany 7 Jul 2021 65 247 345 samples 3 733 519 5 7 77 8 4 5 323 324 nbsp Ghana 3 Jul 2021 1 305 749 samples 96 708 7 4 4 2 0 31 325 nbsp Greece 18 Dec 2022 101 576 831 samples 5 548 487 5 5 943 51 5 326 nbsp Greenland 30 Jan 2022 164 573 samples 10 662 6 5 293 19 0 327 nbsp Grenada 11 May 2021 28 684 161 0 56 25 7 0 14 328 nbsp Guatemala 6 Jan 2023 6 800 560 samples 1 230 098 18 1 39 4 7 1 329 nbsp Guinea 21 Jul 2021 494 898 samples 24 878 5 0 3 8 0 19 259 330 nbsp Guinea Bissau 7 Jul 2022 145 231 8 400 5 8 7 7 0 45 331 nbsp Guyana 15 Jun 2022 648 569 cases 66 129 10 2 82 5 8 4 332 nbsp Haiti 26 Nov 2022 223 475 cases 33 874 15 2 2 0 0 30 333 nbsp Honduras 26 Nov 2021 1 133 782 samples 377 859 33 3 11 8 3 9 334 nbsp Hungary 10 May 2022 11 394 556 samples 1 909 948 16 8 118 19 8 335 nbsp Iceland 9 Aug 2022 1 988 652 samples 203 162 10 2 546 55 8 336 nbsp India 8 Jul 2022 866 177 937 samples 43 585 554 5 0 63 31 7 337 338 nbsp Indonesia 3 Jul 2023 76 062 770 cases 6 812 127 9 0 28 2 2 5 339 340 nbsp Iran 31 May 2022 52 269 202 samples 7 232 268 13 8 62 8 8 7 341 nbsp Iraq 3 Aug 2022 19 090 652 samples 2 448 484 12 8 47 5 6 1 342 nbsp Ireland 31 Jan 2023 12 990 476 samples 1 700 817 13 1 264 34 6 343 nbsp Israel 17 Jan 2022 41 373 364 samples 1 792 137 4 3 451 19 5 344 nbsp Italy 16 Mar 2023 269 127 054 samples 25 651 205 9 5 446 42 5 345 nbsp Ivory Coast 3 Mar 2021 429 177 samples 33 285 7 8 1 6 0 13 346 nbsp Jamaica 30 Sep 2022 1 184 973 samples 151 931 12 8 43 5 5 6 347 nbsp Japan 1 Mar 2021 8 487 288 432 773 5 1 6 7 0 34 348 nbsp Jordan 6 Jun 2021 7 407 053 samples 739 847 10 0 69 5 6 9 349 nbsp Kazakhstan 28 May 2021 11 575 012 samples 385 144 3 3 62 1 2 1 350 nbsp Kenya 5 Mar 2021 1 322 806 samples 107 729 8 1 2 8 0 23 351 nbsp Kosovo 31 May 2021 611 357 cases 107 410 17 6 33 8 5 9 352 nbsp Kuwait 9 Mar 2022 7 754 247 samples 624 573 8 1 181 14 6 353 nbsp Kyrgyzstan 10 Feb 2021 695 415 samples 85 253 12 3 10 7 1 3 354 nbsp Laos 1 Mar 2021 114 030 cases 45 0 039 1 6 0 00063 355 nbsp Latvia 5 Sep 2021 3 630 095 samples 144 518 4 0 189 7 5 356 nbsp Lebanon 14 Jun 2021 4 599 186 samples 542 649 11 8 67 4 8 0 357 nbsp Lesotho 30 Mar 2022 431 221 32 910 7 6 21 5 1 6 358 nbsp Liberia 17 Jul 2021 128 246 5 396 4 2 2 5 0 11 359 nbsp Libya 14 Apr 2022 2 578 215 samples 501 862 19 5 37 6 7 3 259 360 nbsp Lithuania 31 Jan 2023 9 046 584 samples 1 170 108 12 9 324 41 9 361 362 nbsp Luxembourg i 12 May 2022 4 248 188 samples 244 182 5 7 679 39 0 363 nbsp Madagascar 19 Feb 2021 119 608 cases 19 831 16 6 0 46 0 076 364 nbsp Malawi 29 Nov 2022 624 784 samples 88 086 14 1 3 3 0 46 365 nbsp Malaysia 7 Sep 2021 23 705 425 cases 1 880 734 7 9 72 3 5 7 366 nbsp Maldives 13 Mar 2022 2 216 560 samples 174 658 7 9 398 31 3 367 368 nbsp Mali 7 Jul 2021 322 504 samples 14 449 4 5 1 6 0 071 259 369 nbsp Malta 8 Sep 2021 1 211 456 samples 36 606 3 0 245 7 4 370 nbsp Mauritania 16 Apr 2021 268 093 18 103 6 8 6 1 0 41 371 nbsp Mauritius 22 Nov 2020 289 552 samples 494 0 17 22 9 0 039 372 nbsp Mexico 15 Oct 2021 10 503 678 cases 3 749 860 35 7 8 2 2 9 373 nbsp Moldova j 20 Apr 2022 3 213 594 samples 516 864 16 1 122 19 6 374 nbsp Mongolia 10 Jul 2021 3 354 200 cases 136 053 4 1 100 4 1 375 nbsp Montenegro 10 May 2021 394 388 samples 98 449 25 0 62 5 15 6 376 377 nbsp Morocco 6 Jan 2023 14 217 563 cases 1 272 299 8 9 38 5 3 4 378 nbsp Mozambique 22 Jul 2021 688 570 samples 105 866 15 4 2 2 0 34 379 nbsp Myanmar 16 Sep 2021 4 047 680 samples 440 741 10 9 7 4 0 81 380 nbsp Namibia 4 Jul 2022 1 062 663 samples 166 229 15 6 38 7 6 1 381 nbsp Nepal 26 Jul 2022 5 804 358 samples 984 475 17 0 20 7 3 5 382 nbsp Netherlands 6 Jul 2021 14 526 293 cases 1 692 834 11 7 83 4 9 7 383 nbsp New Caledonia 3 Sep 2021 41 962 samples 136 0 32 15 7 0 050 384 nbsp New Zealand 29 Jan 2023 7 757 935 samples 2 136 662 27 5 156 42 9 385 386 nbsp Niger 22 Feb 2021 79 321 cases 4 740 6 0 0 35 0 021 387 nbsp Nigeria 28 Feb 2021 1 544 008 samples 155 657 10 1 0 75 0 076 388 nbsp North Korea 25 Nov 2020 16 914 cases 0 0 0 066 0 389 nbsp North Macedonia 1 Jul 2021 881 870 samples 155 689 17 7 42 5 7 5 390 391 nbsp Northern Cyprus k 12 Jul 2022 7 096 998 samples 103 034 1 5 2 177 31 6 392 nbsp Norway 20 Jan 2022 9 811 888 samples 554 778 5 7 183 10 3 393 nbsp Oman 28 Oct 2020 509 959 samples 114 434 22 4 11 0 2 5 394 nbsp Pakistan 5 Mar 2021 9 173 593 samples 588 728 6 4 4 2 0 27 395 nbsp Palestine 5 Feb 2022 3 078 533 samples 574 105 18 6 60 9 11 4 396 nbsp Panama 28 Jan 2023 7 475 016 samples 1 029 701 13 8 179 24 7 397 nbsp Papua New Guinea 17 Feb 2021 47 490 cases 961 2 0 0 53 0 011 398 nbsp Paraguay 27 Mar 2022 2 609 819 samples 647 950 24 8 36 6 9 1 399 nbsp Peru 17 Nov 2022 36 073 768 samples 4 177 786 11 6 109 9 12 7 400 nbsp Philippines 7 Jan 2023 34 402 980 samples 4 073 980 11 8 34 1 4 0 401 402 nbsp Poland 27 Apr 2022 36 064 311 samples 5 993 861 16 6 94 0 15 6 403 nbsp Portugal 5 Jan 2022 27 515 490 samples 1 499 976 5 5 268 14 6 404 nbsp Qatar 11 Nov 2022 4 061 988 cases 473 440 11 7 141 16 4 405 nbsp Romania 29 Jan 2021 5 405 393 samples 724 250 13 4 27 9 3 7 406 nbsp Russia 6 Jun 2022 295 542 733 samples 18 358 459 6 2 201 12 5 407 408 nbsp Rwanda 6 Oct 2021 2 885 812 samples 98 209 3 4 22 3 0 76 409 nbsp Saint Kitts and Nevis 26 Aug 2021 30 231 cases 995 3 3 57 6 1 9 410 nbsp Saint Lucia 7 Oct 2022 212 132 samples 29 550 13 9 116 6 16 2 411 nbsp Saint Vincent 28 Jan 2023 113 504 cases 9 585 8 4 103 0 8 7 412 nbsp San Marino 29 Jan 2023 192 613 samples 23 427 12 2 563 68 4 413 nbsp Saudi Arabia 26 Apr 2022 41 849 069 samples 753 632 1 8 120 2 2 414 nbsp Senegal 12 Jul 2021 624 502 samples 46 509 7 4 3 9 0 29 415 nbsp Serbia 2 Feb 2023 12 185 475 cases 2 473 599 20 3 175 35 5 416 nbsp Singapore 3 Aug 2021 16 206 203 samples 65 315 0 40 284 1 1 417 418 nbsp Slovakia 2 Feb 2023 7 391 882 samples 1 861 034 25 2 135 34 1 419 nbsp Slovenia 2 Feb 2023 2 826 117 samples 1 322 282 46 8 135 63 1 420 nbsp South Africa 24 May 2021 11 378 282 cases 1 637 848 14 4 19 2 2 8 421 422 nbsp South Korea 1 Mar 2021 6 592 010 samples 90 029 1 4 12 7 0 17 423 nbsp South Sudan 26 May 2021 164 472 10 688 6 5 1 3 0 084 424 nbsp Spain 1 Jul 2021 54 128 524 samples 3 821 305 7 1 116 8 2 425 426 nbsp Sri Lanka 30 Mar 2021 2 384 745 samples 93 128 3 9 10 9 0 43 427 428 nbsp Sudan 7 Jan 2021 158 804 samples 23 316 14 7 0 36 0 053 259 nbsp Sweden 24 May 2021 9 996 795 samples 1 074 751 10 8 96 8 10 4 429 430 nbsp Switzerland l 7 Nov 2022 23 283 909 samples 4 276 836 18 4 270 49 7 431 nbsp Taiwan m 3 Feb 2023 30 275 725 samples 8 622 129 28 48 128 3 36 528 432 nbsp Tanzania 18 Nov 2020 3 880 509 13 1 0 0065 0 00085 259 nbsp Thailand 4 Mar 2021 1 579 597 cases 26 162 1 7 2 3 0 038 433 nbsp Togo 6 Jan 2023 807 269 39 358 4 9 9 4 0 46 434 nbsp Trinidad and Tobago 3 Jan 2022 512 730 cases 92 997 18 1 37 6 6 8 435 nbsp Tunisia 23 Aug 2021 2 893 625 samples 703 732 24 3 24 5 6 0 436 nbsp Turkey 2 Jul 2021 61 236 294 samples 5 435 831 8 9 73 6 6 5 437 nbsp Uganda 11 Feb 2021 852 444 samples 39 979 4 7 1 9 0 087 438 nbsp Ukraine 24 Nov 2021 15 648 456 samples 3 367 461 21 5 37 2 8 0 439 nbsp United Arab Emirates 1 Feb 2023 198 685 717 samples 1 049 537 0 53 2 070 10 9 440 nbsp United Kingdom 19 May 2022 522 526 476 samples 22 232 377 4 3 774 32 9 441 nbsp United States 29 Jul 2022 929 349 291 samples 90 749 469 9 8 281 27 4 442 443 nbsp Uruguay 16 Apr 2022 6 089 116 samples 895 592 14 7 175 25 8 444 nbsp Uzbekistan 7 Sep 2020 2 630 000 samples 43 975 1 7 7 7 0 13 445 nbsp Venezuela 30 Mar 2021 3 179 074 samples 159 149 5 0 11 0 0 55 446 nbsp Vietnam 28 Aug 2022 45 772 571 samples 11 403 302 24 9 46 4 11 6 447 nbsp Zambia 10 Mar 2022 3 301 860 samples 314 850 9 5 19 0 1 8 448 nbsp Zimbabwe 15 Oct 2022 2 529 087 samples 257 893 10 2 17 0 1 7 259 449 Local time For some countries it is unclear whether they report samples or cases One person tested twice is recorded as one case and two samples Excluding Taiwan Excluding Northern Cyprus Excluding Greenland and the Faroe Islands Excluding Overseas France Testing data from 4 May to 12 May is missing because of the transition to the new reporting system SI DEP Excluding Abkhazia and South Ossetia Data for residents only Excluding Transnistria Northern Cyprus is not recognized as a sovereign state by any country except Turkey Includes data for Liechtenstein Not a United Nations member See also2002 2004 SARS outbreak Coronavirus breathalyzer Coronavirus disease 2019 COVID 19 misinformation PCR testing COVID 19 pandemic Philippine government response to the COVID 19 pandemic COVID 19 testing controversyReferences nbsp This article incorporates public domain material from Symptom Based Strategy to Discontinue Isolation for Persons with COVID 19 Centers for Disease Control and Prevention Retrieved 5 May 2020 Coronavirus Disease 2019 COVID 19 U S Centers for Disease Control and Prevention CDC 11 February 2020 Archived from the original on 14 March 2020 Retrieved 9 June 2020 Kobokovich A West R Gronvall G Global Progress on COVID 19 Serology Based Testing Johns Hopkins Center for Health Security Archived from the original on 9 June 2020 Retrieved 9 June 2020 a b c Kubina R Dziedzic A June 2020 Molecular and Serological Tests for COVID 19 a Comparative Review of SARS CoV 2 Coronavirus Laboratory and Point of Care Diagnostics Diagnostics 10 6 434 doi 10 3390 diagnostics10060434 PMC 7345211 PMID 32604919 Test for Past Infection U S Centers for Disease Control and Prevention CDC 2020 Archived from the original on 16 May 2020 Retrieved 19 May 2020 Antibody blood tests also called antibody tests check your blood by looking for antibodies which show if you had a previous infection with the virus Depending on when someone was infected and the timing of the test the test may not find antibodies in someone with a current COVID 19 infection a b c Abbasi J May 2020 The Promise and Peril of Antibody Testing for COVID 19 JAMA 323 19 1881 1883 doi 10 1001 jama 2020 6170 PMID 32301958 Archived from the original on 20 April 2020 Retrieved 20 April 2020 a b Brotschi M 7 March 2020 Bund sucht nicht mehr alle Corona Infizierten The federal government is no longer looking for all those infected with corona Der Bund in German ISSN 0774 6156 Archived from the original on 29 March 2020 Retrieved 9 June 2020 Van Beusekom M 24 March 2020 Italian doctors note high COVID 19 death rate urge action CIDRAP News Archived from the original on 9 June 2020 Retrieved 9 June 2020 a b Otmani M 22 March 2020 COVID 19 First results of the voluntary screening in Iceland Nordic Life Science Archived from the original on 29 March 2020 Retrieved 9 June 2020 a b Ward D April 2020 Sampling bias explaining wide variations in COVID 19 case fatality rates Preprint Bern Switzerland WardEnvironment doi 10 13140 RG 2 2 24953 62564 1 Henriques M 2 April 2020 Coronavirus Why death and mortality rates differ BBC News Archived from the original on 2 April 2020 Retrieved 9 June 2020 a b Ward D May 2020 Sampling Bias Explaining Variations in Age Distributions of COVID 19 Cases Technical Report Report WardEnvironment doi 10 13140 RG 2 2 27321 19047 2 Why More Younger People Are Testing Positive for COVID 19 Time Archived from the original on 26 February 2021 Retrieved 18 August 2020 Mina MJ Parker R Larremore DB November 2020 Rethinking Covid 19 Test Sensitivity A Strategy for Containment The New England Journal of Medicine 383 22 e120 doi 10 1056 NEJMp2025631 PMID 32997903 S2CID 222158786 a b Antigen detection in the diagnosis of SARS CoV 2 infection www who int Retrieved 12 July 2022 a b c CDC 11 February 2020 Guidance for Antigen Testing for SARS CoV 2 for Healthcare Providers Testing Individuals in the Community Centers for Disease Control and Prevention Retrieved 12 July 2022 Siouxsie Wiles amp Toby Morris What we don t know about Covid 19 The Spinoff 6 May 2020 Archived from the original on 22 August 2020 Retrieved 6 May 2020 Testing for COVID 19 U S Centers for Disease Control and Prevention CDC 20 May 2020 Archived from the original on 19 May 2020 Retrieved 20 May 2020 Two kinds of tests are available for COVID 19 viral tests and antibody tests Tanner T 23 September 2020 Finland deploys coronavirus sniffing dogs at main airport Associated Press Helsinki Archived from the original on 27 October 2020 Retrieved 28 October 2020 Jones RT Guest C Lindsay SW Kleinschmidt I Bradley J Dewhirst S et al December 2020 Could bio detection dogs be used to limit the spread of COVID 19 by travellers Journal of Travel Medicine 27 8 doi 10 1093 jtm taaa131 PMC 7454791 PMID 32789466 Jendrny P Schulz C Twele F Meller S von Kockritz Blickwede M Osterhaus AD et al July 2020 Scent dog identification of samples from COVID 19 patients a pilot study BMC Infectious Diseases 20 1 536 doi 10 1186 s12879 020 05281 3 PMC 7376324 PMID 32703188 a b Habibzadeh P Mofatteh M Silawi M Ghavami S Faghihi MA September 2021 Molecular diagnostic assays for COVID 19 an overview Critical Reviews in Clinical Laboratory Sciences 58 6 385 398 doi 10 1080 10408363 2021 1884640 PMC 7898297 PMID 33595397 RNA Extraction AssayGenie Archived from the original on 6 May 2020 Retrieved 7 May 2020 a b How is the COVID 19 Virus Detected using Real Time RT PCR IAEA 27 March 2020 Archived from the original on 1 May 2020 Retrieved 5 May 2020 Curetis Group Company Ares Genetics and BGI Group Collaborate to Offer Next Generation Sequencing and PCR based Coronavirus 2019 nCoV Testing in Europe GlobeNewswire News Room Press release 30 January 2020 Archived from the original on 31 January 2020 Retrieved 1 February 2020 a b Bustin SA Benes V Garson JA Hellemans J Huggett J Kubista M et al April 2009 The MIQE guidelines minimum information for publication of quantitative real time PCR experiments Clinical Chemistry 55 4 611 622 doi 10 1373 clinchem 2008 112797 PMID 19246619 Real time reverse transcription PCR qRT PCR and its potential use in clinical diagnosis PDF Clinical Science 23 September 2005 Archived PDF from the original on 24 November 2020 Retrieved 5 May 2020 The Basics RT PCR ThermoFisher Scientific Archived from the original on 14 April 2020 Retrieved 5 May 2020 Kang XP Jiang T Li YQ Lin F Liu H Chang GH et al June 2010 A duplex real time RT PCR assay for detecting H5N1 avian influenza virus and pandemic H1N1 influenza virus Virology Journal 7 113 doi 10 1186 1743 422X 7 113 PMC 2892456 PMID 20515509 Joyce C 2002 Quantitative RT PCR A Review of Current Methodologies RT PCR Protocols Methods Mol Biol Vol 193 pp 83 92 doi 10 1385 1 59259 283 X 083 ISBN 978 1 59259 283 8 PMID 12325527 Varkonyi Gasic E Hellens RP 2010 QRT PCR of Small RNAs Plant Epigenetics Methods in Molecular Biology Vol 631 pp 109 22 doi 10 1007 978 1 60761 646 7 10 ISBN 978 1 60761 645 0 PMID 20204872 Accelerated Emergency Use Authorization Eua Summary Covid 19 Rt Pcr Test Laboratory Corporation of America FDA Archived from the original on 16 January 2021 Retrieved 3 April 2020 Taylor S Wakem M Dijkman G Alsarraj M Nguyen M April 2010 A practical approach to RT qPCR Publishing data that conform to the MIQE guidelines Methods 50 4 S1 S5 doi 10 1016 j ymeth 2010 01 005 PMID 20215014 Dinnes J Deeks JJ Berhane S Taylor M Adriano A Davenport C et al March 2021 Rapid point of care antigen and molecular based tests for diagnosis of SARS CoV 2 infection The Cochrane Database of Systematic Reviews 3 4 CD013705 doi 10 1002 14651858 CD013705 pub2 PMC 8078597 PMID 33760236 Dinnes J Sharma P Berhane S van Wyk SS Nyaaba N Domen J et al July 2022 Rapid point of care antigen tests for diagnosis of SARS CoV 2 infection The Cochrane Database of Systematic Reviews 2022 7 CD013705 doi 10 1002 14651858 CD013705 pub3 PMC 9305720 PMID 35866452 Real Time RT PCR Panel for Detection 2019 nCoV U S Centers for Disease Control and Prevention CDC 29 January 2020 Archived from the original on 30 January 2020 Retrieved 1 February 2020 a b c Drosten C 26 March 2020 Coronavirus Update Folge 22 Coronavirus update episode 22 PDF NDR Archived PDF from the original on 31 March 2020 Retrieved 2 April 2020 a b Here s where things stand on COVID 19 tests in the U S Science News ScienceNews 17 April 2020 Archived from the original on 28 April 2020 Retrieved 6 May 2020 a b c Xu R Cui B Duan X Zhang P Zhou X Yuan Q April 2020 Saliva potential diagnostic value and transmission of 2019 nCoV International Journal of Oral Science 12 1 11 doi 10 1038 s41368 020 0080 z PMC 7162686 PMID 32300101 Drosten C Gunther S Preiser W van der Werf S Brodt HR Becker S et al May 2003 Identification of a novel coronavirus in patients with severe acute respiratory syndrome The New England Journal of Medicine 348 20 1967 1976 doi 10 1056 NEJMoa030747 hdl 1765 8447 PMID 12690091 Ghoshal U Vasanth S Tejan N June 2020 A guide to laboratory diagnosis of Corona Virus Disease 19 for the gastroenterologists Indian Journal of Gastroenterology 39 3 236 242 doi 10 1007 s12664 020 01082 3 PMC 7462729 PMID 32875524 COVID 19 saliva tests What is the benefit Mayo Clinic 16 April 2020 Archived from the original on 1 May 2020 Retrieved 6 May 2020 a b New Rutgers Saliva Test for Coronavirus Gets FDA Approval Rutgers edu 13 April 2020 Archived from the original on 30 April 2020 Retrieved 1 May 2020 FDA authorizes Covid 19 saliva test for emergency use CNN 14 April 2020 Archived from the original on 27 April 2020 Retrieved 1 May 2020 Wyllie AL Fournier J Casanovas Massana A Campbell M Tokuyama M Vijayakumar P et al September 2020 Saliva or Nasopharyngeal Swab Specimens for Detection of SARS CoV 2 The New England Journal of Medicine 383 13 1283 1286 doi 10 1056 NEJMc2016359 PMC 7484747 PMID 32857487 S2CID 221358482 Service RF August 2020 Spit shines for easier coronavirus testing Science 369 6507 1041 1042 Bibcode 2020Sci 369 1041S doi 10 1126 science 369 6507 1041 PMID 32855317 S2CID 221358939 Yale University School of Public Health finds saliva samples promising alternative to nasopharyngeal swab Merck Manual 29 April 2020 Archived from the original on 28 May 2020 Retrieved 6 April 2020 FDA gives emergency approval to game changer COVID 19 saliva test The Washington Times Archived from the original on 16 August 2020 Retrieved 15 August 2020 Coronavirus COVID 19 Update FDA Issues Emergency Use Authorization to Yale School of Public Health for SalivaDirect Which Uses a New Method of Saliva Sample Processing U S Food and Drug Administration FDA Press release 15 August 2020 Archived from the original on 16 August 2020 Retrieved 6 November 2020 a b nbsp One or more of the preceding sentences incorporates text from this source which is in the public domain Risk of False Results with the Curative SARS Cov 2 Test for COVID 19 U S Food and Drug Administration FDA 4 January 2021 Archived from the original on 4 January 2021 Retrieved 4 January 2021 Symptom Based Strategy to Discontinue Isolation for Persons with COVID 19 2020 referenced CDC unpublished data COVID 19 Investigation Team June 2020 Clinical and virologic characteristics of the first 12 patients with coronavirus disease 2019 COVID 19 in the United States Nature Medicine 26 6 861 868 doi 10 1038 s41591 020 0877 5 PMID 32327757 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint numeric names authors list link Young BE Ong SW Kalimuddin S Low JG Tan SY Loh J et al April 2020 Epidemiologic Features and Clinical Course of Patients Infected With SARS CoV 2 in Singapore JAMA 323 15 1488 1494 doi 10 1001 jama 2020 3204 PMC 7054855 PMID 32125362 Zou L Ruan F Huang M Liang L Huang H Hong Z et al March 2020 SARS CoV 2 Viral Load in Upper Respiratory Specimens of Infected Patients The New England Journal of Medicine 382 12 1177 1179 doi 10 1056 NEJMc2001737 PMC 7121626 PMID 32074444 Wolfel R Corman VM Guggemos W Seilmaier M Zange S Muller MA et al May 2020 Virological assessment of hospitalized patients with COVID 2019 Nature 581 7809 465 469 Bibcode 2020Natur 581 465W doi 10 1038 s41586 020 2196 x PMID 32235945 Symptom Based Strategy to Discontinue Isolation for Persons with COVID 19 2020 referenced CDC unpublished data Young et al 2020 Symptom Based Strategy to Discontinue Isolation for Persons with COVID 19 2020 referenced CDC unpublished data COVID 19 Investigation Team June 2020 Clinical and virologic characteristics of the first 12 patients with coronavirus disease 2019 COVID 19 in the United States Nature Medicine 26 6 861 868 doi 10 1038 s41591 020 0877 5 PMID 32327757 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint numeric names authors list link Zimmer C 5 May 2020 With Crispr a Possible Quick Test for the Coronavirus The New York Times ISSN 0362 4331 Archived from the original on 14 May 2020 Retrieved 14 May 2020 STOPCovid stopcovid science Archived from the original on 10 June 2020 Retrieved 14 June 2020 Joung J Ladha A Saito M Segel M Bruneau R Huang MW et al May 2020 Point of care testing for COVID 19 using SHERLOCK diagnostics medRxiv 10 1101 2020 05 04 20091231v1 a b c d e f Developing Antibodies and Antigens for COVID 19 Diagnostics Technology Networks 6 April 2020 Archived from the original on 30 April 2020 Retrieved 30 April 2020 Guglielmi G September 2020 Fast coronavirus tests what they can and can t do Nature 585 7826 496 498 Bibcode 2020Natur 585 496G doi 10 1038 d41586 020 02661 2 PMID 32939084 S2CID 221768935 CDC 11 February 2020 COVID 19 and Your Health Centers for Disease Control and Prevention Retrieved 12 July 2022 Remarks by President Trump Vice President Pence and Members of the Coronavirus Task Force in Press Briefing whitehouse gov 17 April 2020 Archived from the original on 20 January 2021 Retrieved 30 April 2020 via National Archives Mullender F 11 March 2021 Grundschulen Corona Pool Tests gelten als kindgerecht unkompliziert und sicher in German Deutschlandfunk Archived from the original on 24 July 2021 Retrieved 5 June 2021 NIH launches competition to speed COVID 19 diagnostics AAAS 29 April 2020 Archived from the original on 1 May 2020 Retrieved 1 May 2020 a b What to know about the three main types of coronavirus tests CNN 29 April 2020 Archived from the original on 10 May 2020 Retrieved 30 April 2020 a b Dinnes J Deeks JJ Berhane S Taylor M Adriano A Davenport C et al Cochrane COVID 19 Diagnostic Test Accuracy Group March 2021 Rapid point of care antigen and molecular based tests for diagnosis of SARS CoV 2 infection The Cochrane Database of Systematic Reviews 3 3 CD013705 doi 10 1002 14651858 CD013705 pub2 PMC 8078597 PMID 33760236 Rapid Tests Rapid Tests Archived from the original on 31 May 2021 Retrieved 2 July 2021 Shaw J 3 August 2020 Failing the Coronavirus Testing Test Harvard Magazine Archived from the original on 30 June 2021 Retrieved 2 July 2021 a b Office of the Commissioner 9 May 2020 Coronavirus COVID 19 Update FDA Authorizes First Antigen Test to Help in the Rapid Detection of the Virus that Causes COVID 19 in Patients FDA Archived from the original on 29 May 2021 Retrieved 2 July 2021 a b c d Klasse PJ 9 September 2014 Neutralization of Virus Infectivity by Antibodies Old Problems in New Perspectives Advances in Biology 2014 Hindawi Limited 1 24 doi 10 1155 2014 157895 PMC 4835181 PMID 27099867 The next frontier in coronavirus testing Identifying the full scope of the pandemic not just individual infections STAT 27 March 2020 Archived from the original on 29 June 2020 Retrieved 30 April 2020 a b Tang EW Bobenchik AM Lu S September 2020 Testing for SARS CoV 2 COVID 19 A General Review Rhode Island Medical Journal 103 8 20 23 PMID 32900007 What Immunity to COVID 19 Really Means Scientific American 10 April 2020 Archived from the original on 28 April 2020 a b Fox Tilly Geppert Julia Dinnes Jacqueline Scandrett Katie Bigio Jacob Sulis Giorgia Hettiarachchi Dineshani Mathangasinghe Yasith Weeratunga Praveen Wickramasinghe Dakshitha Bergman Hanna Buckley Brian S Probyn Katrin Sguassero Yanina Davenport Clare 17 November 2022 Antibody tests for identification of current and past infection with SARS CoV 2 The Cochrane Database of Systematic Reviews 2022 11 CD013652 doi 10 1002 14651858 CD013652 pub2 ISSN 1469 493X PMC 9671206 PMID 36394900 Cellex Emergency Use Authorization FDA 1 April 2020 Archived from the original on 9 April 2020 Retrieved 10 April 2020 Will an Antibody Test Allow Us to Go Back to School or Work The New York Times 10 April 2020 Archived from the original on 15 April 2020 Retrieved 15 April 2020 Mount Sinai Emergency Use Authorization FDA 15 April 2020 Retrieved 18 April 2020 Bauer G January 2021 The variability of the serological response to SARS corona virus 2 Potential resolution of ambiguity through determination of avidity functional affinity Journal of Medical Virology 93 1 311 322 doi 10 1002 jmv 26262 PMC 7361859 PMID 32633840 Ravi N Cortade DL Ng E Wang SX October 2020 Diagnostics for SARS CoV 2 detection A comprehensive review of the FDA EUA COVID 19 testing landscape Biosensors amp Bioelectronics 165 112454 doi 10 1016 j bios 2020 112454 PMC 7368663 PMID 32729549 Goudouris ES 2020 Laboratory diagnosis of COVID 19 Jornal de Pediatria 97 1 7 12 doi 10 1016 j jped 2020 08 001 PMC 7456621 PMID 32882235 a b c d Global Progress on COVID 19 Serology Based Testing Johns Hopkins Center for Health Security Archived from the original on 14 June 2020 Retrieved 14 June 2020 a b Tan CW Chia WN Qin X Liu P Chen MI Tiu C et al September 2020 A SARS CoV 2 surrogate virus neutralization test based on antibody mediated blockage of ACE2 spike protein protein interaction Nature Biotechnology 38 9 1073 1078 doi 10 1038 s41587 020 0631 z PMID 32704169 S2CID 220720953 a b c Mallapaty S April 2020 Will antibody tests for the coronavirus really change everything Nature 580 7805 571 572 Bibcode 2020Natur 580 571M doi 10 1038 d41586 020 01115 z PMID 32313159 S2CID 216048544 Archived from the original on 24 June 2020 Retrieved 20 April 2020 a b c Q amp A on COVID 19 Antibody Tests factcheck org 27 April 2020 Archived from the original on 27 April 2020 Retrieved 28 April 2020 Neutralising antibody Biology Online 2008 Archived from the original on 8 July 2018 Retrieved 4 July 2009 Schmaljohn AL July 2013 Protective antiviral antibodies that lack neutralizing activity precedents and evolution of concepts Current HIV Research 11 5 345 353 doi 10 2174 1570162x113116660057 PMID 24191933 Rhorer J Ambrose CS Dickinson S Hamilton H Oleka NA Malinoski FJ Wittes J February 2009 Efficacy of live attenuated influenza vaccine in children A meta analysis of nine randomized clinical trials Vaccine 27 7 Virology Blog 1101 1110 doi 10 1016 j vaccine 2008 11 093 PMID 19095024 Archived from the original on 23 April 2020 Retrieved 29 April 2020 expert reaction to announcement by Roche of its new serology test for COVID 19 antibodies Science Media Centre 17 April 2020 Archived from the original on 30 April 2020 Retrieved 28 April 2020 Cao WC Liu W Zhang PH Zhang F Richardus JH September 2007 Disappearance of antibodies to SARS associated coronavirus after recovery The New England Journal of Medicine 357 11 NEJM 1162 1163 doi 10 1056 NEJMc070348 PMID 17855683 a b Lack of Peripheral Memory B Cell Responses in Recovered Patients with Severe Acute Respiratory Syndrome A Six Year Follow Up Study PDF Journal of Immunology 19 April 2011 Archived PDF from the original on 1 May 2020 Retrieved 1 May 2020 Leslie M May 2020 T cells found in coronavirus patients bode well for long term immunity Science 368 6493 809 810 Bibcode 2020Sci 368 809L doi 10 1126 science 368 6493 809 PMID 32439770 S2CID 218834495 Calvo Henriquez C Maldonado Alvarado B Chiesa Estomba C Rivero Fernandez I Sanz Rodriguez M Villarreal IM et al October 2020 Ethyl alcohol threshold test a fast reliable and affordable olfactory Assessment tool for COVID 19 patients European Archives of Oto Rhino Laryngology 277 10 2783 2792 doi 10 1007 s00405 020 06131 3 PMC 7312102 PMID 32583183 Hayes J Exten C State P 24 December 2020 At home DIY smell tests could catch Covid 19 cases CNN Health The Conversation Retrieved 7 September 2021 Menni C Sudre CH Steves CJ Ourselin S Spector TD November 2020 Widespread smell testing for COVID 19 has limited application Authors reply Lancet 396 10263 1630 1631 doi 10 1016 S0140 6736 20 32316 3 PMC 7832202 PMID 33157000 a b c Salehi S Abedi A Balakrishnan S Gholamrezanezhad A July 2020 Coronavirus Disease 2019 COVID 19 A Systematic Review of Imaging Findings in 919 Patients AJR American Journal of Roentgenology 215 1 87 93 doi 10 2214 AJR 20 23034 PMID 32174129 Known features of COVID 19 on initial CT include bilateral multilobar ground glass opacification GGO with a peripheral or posterior distribution mainly in the lower lobes and less frequently within the right middle lobe Manigandan S Wu MT Ponnusamy VK Raghavendra VB Pugazhendhi A Brindhadevi K November 2020 A systematic review on recent trends in transmission diagnosis prevention and imaging features of COVID 19 Process Biochemistry 98 233 240 doi 10 1016 j procbio 2020 08 016 PMC 7439988 PMID 32843849 Lee EY Ng MY Khong PL April 2020 COVID 19 pneumonia what has CT taught us The Lancet Infectious Diseases 20 4 384 385 doi 10 1016 S1473 3099 20 30134 1 PMC 7128449 PMID 32105641 ACR Recommendations for the use of Chest Radiography and Computed Tomography CT for Suspected COVID 19 Infection American College of Radiology 22 March 2020 Archived from the original on 13 May 2020 Retrieved 20 May 2020 a b c Tabik S Gomez Rios A Martin Rodriguez JL Sevillano Garcia I Rey Area M Charte D et al December 2020 COVIDGR Dataset and COVID SDNet Methodology for Predicting COVID 19 Based on Chest X Ray Images IEEE Journal of Biomedical and Health Informatics 24 12 3595 3605 doi 10 1109 JBHI 2020 3037127 hdl 10045 110797 PMC 8545181 PMID 33170789 S2CID 219179286 span, wikipedia, wiki, book, books, library,

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