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COVID-19 testing can identify the SARS-CoV-2 virus and includes methods that detect the presence of the virus itself (RT-PCR, isothermal nucleic acid amplification, antigen) and those that detect antibodies produced in response to infection. Detection of antibodies (serological tests) can be used both for diagnosis and for population surveillance. Antibody tests show how many people have had the disease, including those whose symptoms were minor or who were asymptomatic, but may not find antibodies in someone with a current COVID-19 infection since antibodies may not show up for weeks. An accurate mortality rate of the disease and the level of herd immunity in the population can be determined from the results of this test. However, the duration and effectiveness of this immune response are still unclear.
Due to limited testing, as of March 2020 no countries had reliable data on the prevalence of the virus in their population. As of 24 May, countries that publicised their testing data have typically performed many tests equal to 2.6 percent of their population, and no country has tested samples equal to more than 17.3% of its population. There are variations in how much testing has been done across countries. This variability is also likely to be affecting reported case fatality rates, which have probably been overestimated in many countries, due to sampling bias.
There are two broad categories of test: a viral test for a current infection, or an antibody test for the past presence of the virus. The CDC does not currently recommend testing for COVID-19 using a CT scan or looking for low oxygen levels.
Polymerase chain reaction
Polymerase chain reaction (PCR) is a process that causes a very small well-defined segment of DNA to be amplified, or multiplied many hundreds of thousands of times, so there is enough of it to be detected and analyzed. Viruses such as SARS-CoV-2 do not contain DNA but only RNA. When a respiratory sample is collected from the person being tested it is treated with certain chemicals which break down extraneous substances and allow the RNA to be removed from the sample and tested. Reverse transcription polymerase chain reaction (RT-PCR) is a technique that first uses reverse transcription to convert the extracted RNA into DNA and then uses PCR to amplify a piece of the resulting DNA, creating enough to be examined in order to determine if it matches the genetic code of SARS-CoV-2. Real-time PCR (qPCR) provides advantages during the PCR portion of this process, including automating it and enabling high-throughput and more reliable instrumentation, and has become the preferred method. Altogether, the combined technique has been described as real-time RT-PCR or quantitative RT-PCR and is sometimes abbreviated qRT-PCR or rRT-PCR or RT-qPCR, although sometimes just RT-PCR or PCR is used as an abbreviation. The Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines propose that the term RT-qPCR be used, but not all authors adhere to this. The test can be done on respiratory samples obtained by various methods, including a nasopharyngeal swab or sputum sample, as well as on saliva. 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." Results are generally available from within a few hours to two days.
When testing an infected person the likelihood of detecting the virus depends on how much time has passed since the person was infected. According to Christian Drosten the RT-PCR test performed with throat swabs is reliable only in the first week of the disease. Later on the virus can disappear in the throat while it continues to multiply in the lungs. For infected people tested in the second week, alternatively sample material can then be taken from the deep airways by suction catheter, or coughed up material (sputum) can be used.
Saliva has been shown to be a common and transient medium for virus transmission and results provided to the FDA suggest that testing saliva may be as effective as nasal and throat swabs. The FDA has granted Emergency Use Authorization for a test that collects saliva instead of using the traditional nasal swab. It is believed this will reduce the risk for health care professionals, will be much more comfortable for the patient, and will enable quarantined people to collect their own samples more efficiently. According to some experts it is too early to know the operating characteristics of the saliva test, and whether it will prove to be as sensitive as the nasopharyngeal swab test. Some studies suggest that the diagnostic value of saliva depends on how saliva specimens are collected (from deep throat, from oral cavity, or from salivary glands). A recent test conducted by the Yale University School of Public Health found that saliva yielded greater detection sensitivity and consistency throughout the course of infection when compared with samples taken with nasopharyngeal swabs.
Demonstration of a nasopharyngeal swab for COVID-19 testing
Demonstration of a throat swab for COVID-19 testing
Isothermal amplification assays
There are a number of isothermal nucleic acid amplification methods that, just like PCR, amplify a piece of the virus's genome, but are faster than PCR because they don't involve repeated cycles of heating and cooling the sample. These tests typically detect the amplified virus sequences using fluorescent tags, which have to be read out with specialized machines. In one new development, the CRISPR gene editing technology was modified to detect the viral sequences instead: if the modified CRISPR enzyme attaches to the sequence, it releases a signal which colors a paper strip. The researchers expect the resulting test to be cheap and easy to use in patient-care settings.
An antigen is the part of a pathogen that elicits an immune response. The antigen tests look for proteins from the surface of the virus. In the case of a coronavirus, these are usually proteins from the surface spikes, and a nasal swab is used to collect samples. One of the difficulties has been finding a protein target unique to SARS-CoV-2.
Antigen tests are seen as one way to scale up testing to levels necessary to detect acute infection on the scale required. Isothermal nucleic acid amplification tests, can process only one sample at a time per machine. RT-PCR tests are accurate but it takes too much time, energy and trained personnel to run the tests. "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. "But there might be with the antigen test."
An antigen test works by taking a nasal swab from a patient and exposing that to paper strips containing artificial antibodies designed to bind to coronavirus antigens. Any antigens that are present will bind to the strips and give a visual readout. The process takes less than 30 minutes, can deliver results on the spot, and does not require expensive equipment or extensive training.
In respiratory viruses often there is not enough of the antigen material present in the nasal swab to be detectable. This would especially be true with people who are asymptomatic and who have very little if any nasal discharge. Unlike the RT-PCR test, which amplifies very small amounts of genetic material so there is enough to detect, there is no amplification of viral proteins in an antigen test. According to the World Health Organization (WHO) the sensitivity of similar antigen tests for respiratory diseases like the flu ranges between 34% and 80%. "Based on this information, half or more of COVID-19 infected patients might be missed by such tests, depending on the group of patients tested," the WHO said. Many scientists doubt whether an antigen test can be made reliable enough in time to be useful against COVID-19. According to the FDA, positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection. Therefore, negative results from an antigen test may need to be confirmed with a PCR test.
Chest CT scans and chest x-rays are not recommended for diagnosing COVID-19. Radiologic findings in COVID-19 are not specific. Typical features on CT initially include bilateral multilobar ground-glass opacities with a peripheral or posterior distribution. Subpleural dominance, crazy paving, and consolidation may develop as the disease evolves.
Serology tests rely on drawn blood, not a nasal or throat swab, and can identify people who were infected and have already recovered from COVID-19, including those who did not know they had been infected. As of April 2020[update], most serology tests were in the research stage of development.
Part of the immune response to infection is the production of antibodies including IgM and IgG. According to the FDA, IgM antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although levels over the course of infection are not well characterized. IgG antibodies to SARS-CoV-2 generally become detectable 10–14 days after infection although they may be detected earlier, and normally peak around 28 days after the onset of infection. Since antibodies are slow to present they are not the best markers of acute infection, but as they may persist in the bloodstream for many years they are ideal for detecting historic infections.
Antibody tests can be used to determine the percentage of a population that have contracted the disease and are therefore presumably immune. However, it is still not clear how broad and how long and how effective this immune response is. As of April 2020[update] "[s]ome countries are considering issuing so-called immunity passports or risk-free certificates to people who have antibodies against Covid-19, enabling them to travel or return to work assuming that they are protected against reinfection." However, according to the World Health Organization as of 24 April 2020, "There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection." One of the reasons for the uncertainty is that most, if not all, of the current COVID-19 antibody testing done at large scale is for detection of binding antibodies only and does not measure neutralizing antibodies. A neutralizing antibody (NAb) is an antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. A binding antibody will bind to the pathogen but the pathogen remains infective; the purpose can be to flag the pathogen for destruction by the immune system. It may even enhance infectivity by interacting with receptors on macrophages. Since most COVID-19 antibody tests will return a positive result if they find only binding antibodies these tests cannot indicate that the person being tested has generated any NAbs which would give him or her protection against re-infection.
It is normally expected that if binding antibodies are detected the person also has generated NAbs and for many viral diseases total antibody responses correlate somewhat with NAb responses but this is not yet known for COVID-19. A study of 175 people in China who had recovered from COVID‑19 and had mild symptoms reported that 10 individuals had produced no detectable NAbs at the time of discharge, nor did they develop NAbs thereafter. How these patients recovered without the help of NAbs and whether they were at risk of re-infection of SARS-CoV-2 was left for further exploration. An additional source of uncertainty is that even if NAbs are present, several viruses, such as HIV, have evolved mechanisms to evade NAb responses. While this needs to be examined in the context of COVID-19 infection, past experiences with viral infection, in general, argue that in most recovered patients NAb level is a good indicator of protective immunity.
The issue of NAbs was implicated when five sailors from the USS Theodore Roosevelt (CVN-71) who tested positive went through two weeks of isolation, then tested negative twice, and thereafter again tested positive. IgG antibodies normally peak around 28 days after the onset of infection and the time frame of these events is not available.
It is presumed that once a person has been infected his or her chance of getting a second infection two to three months later is low, but how long that protective immunity might last is not known. One study determined that reinfection at 29 days post-infection could not occur in SARS-CoV-2 infected rhesus macaques. Studies have indicated that NAbs to the original SARS virus (the predecessor to the current SARS-CoV-2) can remain active in most people for two years and are gone after six years. Nevertheless, memory cells including Memory B cells and Memory T cells can last much longer and may have the ability to greatly lessen the severity of a reinfection.
Blood from pipette is then placed onto a COVID-19 rapid diagnostic test device.
United States Centers for Disease Control and Prevention (CDC) updated the following information and recommendation in a "Decision Memo" on 3 May. At this time, data are limited regarding how long after infection people continue to shed infectious SARV-CoV-2 RNA, and can therefore still infect others. Key findings are summarized here.
- Viral burden measured in upper respiratory specimens declines after onset of illness.
- At this time, replication-competent virus has not been successfully cultured more than nine days after onset of illness. The statistically estimated likelihood of recovering replication-competent virus approaches zero by 10 days.
- As the likelihood of isolating replication-competent virus decreases, anti-SARS-CoV-2 IgM and IgG can be detected in an increasing number of persons recovering from infection.
- Attempts to culture virus from upper respiratory specimens have been largely unsuccessful when viral burden is in low but detectable ranges (i.e., Ct values higher than 33-35)
- Following recovery from clinical illness, many patients no longer have detectable viral RNA in upper respiratory specimens. Among those who continue to have detectable RNA, concentrations of detectable RNA three days following recovery are generally in the range at which replication-competent virus has not been reliably isolated by CDC.
- No clear correlation has been described between length of illness and duration of post-recovery shedding of detectable viral RNA in upper respiratory specimens.
- Infectious virus has not been cultured from urine or reliably cultured from feces; these potential sources pose minimal if any risk of transmitting infection and any risk can be sufficiently mitigated by good hand hygiene.
For an emerging pathogen like SARS-CoV-2, the patterns and duration of illness and infectivity have not been fully described. However, available data indicate that shedding of SARS-CoV-2 RNA in upper respiratory specimens declines after onset of symptoms. At 10 days after illness onset, recovery of replication-competent virus in viral culture (as a proxy of the presence of infectious virus) is decreased and approaches zero. Although persons may produce PCR-positive specimens for up to six weeks, it remains unknown whether these PCR-positive samples represent the presence of infectious virus. After clinical recovery, many patients do not continue to shed SARS-CoV-2 viral RNA. Among recovered patients with detectable RNA in upper respiratory specimens, concentrations of RNA after three days are generally in ranges where virus has not been reliably cultured by CDC. These data have been generated from adults across a variety of age groups and with varying severity of illness. Data from children and infants are not presently available.
Minimum testing necessary
According to epidemiologists, as lockdown measures are being relaxed effective containment of the pandemic in the United States will not be possible until all infected people can be rapidly located and isolated before they have a chance to infect others, and this will require widespread testing of people before they even begin to show symptoms. The contagiousness of a disease is indicated by the basic reproduction number (R0) of the disease. The R0 (pronounced "R naught") of SARS-CoV-2 in general is thought to be from 2.2 to 2.5, meaning that in a population where all individuals are susceptible to infection, each infected person is expected to infect 2.2 to 2.5 other people. However this can vary from location to location. In New York state the R0 is 3.4 to 3.8. One factor that increases the difficulty of blocking the spread of SARS-CoV-2 is that, on average, an infected person begins showing symptoms five days after becoming infected (the "incubation period") and begins infecting others two to three days before symptoms appear. According to a recent study, an estimated 44% of viral transmissions occur within this period. In addition to this, a significant number of infected people never show symptoms but are nevertheless contagious. Therefore, if transmission of this disease is to be blocked effectively, people must be tested and isolated before they begin to show symptoms.
According to Harvard's Global Health Institute, the U.S. should be doing more than 900,000 tests per day as a country. Other organizations have given varying estimates of up to 23 million tests per day. For the week ending 30 May there were an average of 387,000 tests per day in the United States. According to the World Health Organization if more than 10% of the tests given are coming back positive then not enough testing is being done. How close each state is to the minimum number of tests it should be performing according to the Harvard Global Health Institute estimate, and to the 10% target, as of 6 May, is shown here.
According to some epidemiologists, this huge increase in testing will require that states build a much-expanded testing infrastructure. This would include mobile testing programs and neighborhood testing sites, allowing special attention to be given to high-risk groups such as those in long term-care facilities; the homeless and those working in shelters; employees in high-density workplaces; and anyone who has had close contact with a known COVID-19 patient. Such people would be tested every five days.
Paul Romer believes the U.S. already has the technical capacity to scale up to 20 million tests per day, which is his estimate as to the number that will be necessary to fully remobilize the economy. According to the Edmond J. Safra Center for Ethics this capacity can be available by late July. Romer points to the Single-molecule real-time sequencing equipment from Pacific Biosciences, which is in use in 20 laboratories in the U.S. and to the Ion Torrent Next-Generation Sequencing equipment from ThermoFisher Scientific, which is in use in 16 laboratories in the U.S. According to Romer, "Recent research papers suggest that any one of these has the potential to scale up to millions of tests per day." He adds that this plan would also require removing restrictive regulatory hurdles managed by the FDA. Romer estimates that this amount of testing would require that the Congress allocate $100 billion to generate a revenue stream for labs to rapidly expand testing capability.
Also according to Paul Romer, even a relatively inaccurate test, if administered frequently enough, can produce successful results. He ran simulations in which 7% of the population is tested every day with a test that has a 20% false negative rate (20% of the people who are actually infected will get a negative test result because of a bad swab or a very low level of virus in the early stage of infection) and a 1% false positive rate. The average person would be tested roughly every two weeks and those who tested positive would go into quarantine. Romer concluded that the fraction of the population that is currently infected (known as the attack rate) peaks early, reaching roughly 8% of the population in about thirty days and then gradually declines, in most runs reaching zero at 500 days, with the cumulative fraction of the population that is ultimately infected kept below 20%. Romer adds that these results are indicative, not predictive about the true behavior of the spread of the virus, and should not be taken as being something one can rely on.
Approaches to testing
After issues with testing accuracy and capacity during January and February, the United States was conducting an average of 363,000 tests per day for the week ending 17 May. In comparison, several European countries have been conducting more daily tests per capita than the United States. Three European countries are aiming to conduct 100,000 tests per day—Germany by mid-April, the United Kingdom by the end of April and France by the end of June. Germany has a large medical diagnostics industry, with more than a hundred testing labs that provided the technology and infrastructure to enable rapid increases in testing. The UK sought to diversify its life sciences companies into diagnostics to scale up testing capacity.
In Germany, the National Association of Statutory Health Insurance Physicians said on 2 March that it had a capacity for about 12,000 tests per day in the ambulatory setting and 10,700 had been tested in the prior week. Costs are borne by the health insurance when the test is ordered by a physician. According to the president of the Robert Koch Institute, Germany has an overall capacity for 160,000 tests per week. As of 19 March drive-in tests were offered in several large cities. As of 26 March, the total number of tests performed in Germany was unknown, because only positive results are reported. Health minister Jens Spahn estimated 200,000 tests per week. A first lab survey revealed that as of the end of March a total of at least 483,295 samples were tested and 33,491 samples (6.9%) tested positive for SARS-CoV-2.
By the start of April, the United Kingdom was delivering around 10,000 swab tests per day. It set a target for 100,000 per day by the end of April, eventually rising to 250,000 tests per day. The British NHS has announced that it is piloting a scheme to test suspected cases at home, which removes the risk of a patient infecting others if they come to a hospital or having to disinfect an ambulance if one is used.
In drive-through testing for COVID‑19 for suspected cases, a healthcare professional takes sample using appropriate precautions. Drive-through centers have helped South Korea do some of the fastest, most-extensive testing of any country. Hong Kong has set up a scheme where suspected patients can stay home, "[the] emergency department will give a specimen tube to the patient", they spit into it, send it back and get a test result a while after.
In Israel, researchers at Technion and Rambam Hospital developed and tested a method for testing samples from 64 patients simultaneously, by pooling the samples and only testing further if the combined sample is found to be positive. Pool testing was then adopted in Israel, Germany, South Korea, and Nebraska, and the Indian states Uttar Pradesh, West Bengal, Punjab, Chhattisgarh, and Maharashtra.
In Wuhan a makeshift 2000-sq-meter emergency detection laboratory named "Huo-Yan" (Chinese: 火眼, "Fire Eye") was opened on 5 February 2020 by BGI, which can process more than 10,000 samples a day. With the construction overseen by BGI-founder Wang Jian and taking 5-days, modelling has show cases in Hubei would have been 47% higher and the corresponding cost of tackling the quarantine would have doubled if this testing capacity had not come into operation. The Wuhan Laboratory has been promptly followed by Huo-Yan labs in Shenzhen, Tianjin, Beijing, and Shanghai, in a total of 12 cities across China. By 4 March the daily throughput totals were 50,000 tests per day.
Open source, multiplexed designs released by Origami Assays have been released that can test as many as 1122 patient samples for COVID-19 using only 93 assays. These balanced designs can be run in small laboratories without the need for robotic liquid handlers.
By March, shortages and insufficient amounts of reagent has become a bottleneck for mass testing in the EU and UK and the U.S. This has led some authors to explore sample preparation protocols that involve heating samples at 98 °C (208 °F) for five minutes to release RNA genomes for further testing.
On 31 March it was announced United Arab Emirates was now testing more of its population for Coronavirus per head than any other country, and was on track to scale up the level of testing to reach the bulk of the population. This was through a combination of drive-through capability, and purchasing a population-scale mass-throughput laboratory from Group 42 and BGI (based on their "Huo-Yan" emergency detection laboratories in China). Constructed in 14 days, the lab is capable of conducting tens of thousands RT-PCR tests per day and is the first in the world of this scale to be operational outside of China.
On 8 April 2020, In India, the Supreme Court of India ruled that private labs should be reimbursed at the appropriate time for COVID-19 tests However private labs have stated that they are unable to scale up the testing because of the price cap put on the testing and labs being forced to make advance payment to suppliers while they receive deferred payment from hospitals.
University of California San Francisco conducted PCR tests of 1,845 people in Bolinas, California on 20–24 April, almost the entire town. No active infections were detected. Antibody testing was also performed but the results are not yet available.
In a Stanford study led by Jay Bhattacharya, an antibody test was conducted on 5,603 major league baseball employees and 0.7% tested positive, showing they had been infected in the past. 70% of those who tested positive had had no symptoms.
Production and volume
Different testing recipes targeting different parts of the coronavirus genetic profile were developed in China, France, Germany, Hong Kong, Japan, the United Kingdom, and the United States. The World Health Organization adopted the German recipe for manufacturing kits sent to low-income countries without the resources to develop their own. The German recipe was published on 17 January 2020; the protocol developed by the United States Centers for Disease Control and Prevention (CDC) was not available until 28 January, delaying available tests in the U.S.
China and the United States had problems with the reliability of test kits early in the outbreak, and these countries and Australia were unable to supply enough kits to satisfy demand and recommendations for testing by health experts. In contrast, experts say South Korea's broad availability of testing helped reduce the spread of the novel coronavirus. Testing capacity, largely in private sector labs, was built up over several years by the South Korean government. On 16 March, the World Health Organization called for ramping up the testing programmes as the best way to slow the advance of COVID‑19 pandemic.
High demand for testing due to wide spread of the virus caused backlogs of hundreds of thousands of tests at private U.S. labs, and supplies of swabs and chemical reagents became strained. On 25 May 2020, the U.S. federal government released details on testing that required each state to be responsible for carrying out its own planning and supply needs, which it said would be sufficiently address capacity issues. The proposal was panned for creating competition amongst the states to navigate national and international supply chains.
All tests that have received an Emergency Use Authorization are listed at the FDA website. PCR-based and isothermal nucleic amplification tests are listed with “Molecular” in the technology column. Antibody tests are listed with “Serology” as the technology.
Some community-based testing sites in the United States are listed at the HHS website. Additional testing sites can be found here as well as at state and local health department websites. Nearby testing sites can also be located on Apple maps and Google maps by searching for "COVID-19 test".
When scientists from China first released information on the COVID‑19 viral genome on 11 January 2020, the Malaysian Institute for Medical Research (IMR) successfully produced the "primers and probes" specific to SARS-CoV-2 on the very same day. The IMR's laboratory in Kuala Lumpur had initiated early preparedness by setting up reagents to detect coronavirus using the RT-PCR method. The WHO reagent sequence (primers and probes) released several days later was very similar to that produced in the IMR's laboratory, which was used to diagnose Malaysia's first COVID‑19 patient on 24 January 2020.
Public Health England developed a test by 10 January, using real-time RT-PCR (RdRp gene) assay based on oral swabs. The test detected the presence of any type of coronavirus including specifically identifying SARS-CoV-2. It was rolled out to twelve laboratories across the United Kingdom on 10 February. Another early PCR test was developed by Charité in Berlin, working with academic collaborators in Europe and Hong Kong, and published on 23 January. It used rtRT-PCR, and formed the basis of 250,000 kits for distribution by the World Health Organization (WHO). The South Korean company Kogenebiotech developed a clinical grade, PCR-based SARS-CoV-2 detection kit (PowerChek Coronavirus) approved by Korea Centers for Disease Control and Prevention (KCDC) on 4 February 2020. It looks for the "E" gene shared by all beta coronaviruses, and the RdRp gene specific to SARS-CoV-2.
In the United States, the CDC distributed its SARS-CoV-2 Real Time PCR Diagnostic Panel to public health labs through the International Reagent Resource. One of three genetic tests in older versions of the test kits caused inconclusive results due to faulty reagents, and a bottleneck of testing at the CDC in Atlanta; this resulted in an average of fewer than 100 samples a day being successfully processed throughout the whole of February 2020. Tests using two components were not determined to be reliable until 28 February 2020, and it was not until then that state and local laboratories were permitted to begin testing. The test was approved by the FDA under an EUA.
U.S. commercial labs began testing in early March 2020. As of 5 March LabCorp announced nationwide availability of COVID‑19 testing based on RT-PCR. Quest Diagnostics similarly made nationwide COVID‑19 testing available as of 9 March.
In Russia, the first COVID‑19 test was developed by the State Research Center of Virology and Biotechnology VECTOR, production began on 24 January. On 11 February 2020 the test was approved by the Federal Service for Surveillance in Healthcare.
On 18 March 2020, the FDA issued EUA to Abbott Laboratories for a test on Abbott's m2000 system; the FDA had previously issued similar authorization to Hologic, LabCorp, and Thermo Fisher Scientific. On 21 March 2020, Cepheid similarly received an EUA from the FDA for a test that takes about 45 minutes on its GeneXpert system; the same system that runs the GeneXpert MTB/RIF.
On 13 April, Health Canada approved a test from Spartan Bioscience. Institutions may "test patients" with a handheld DNA analyzer "and receive results without having to send samples away to a [central] lab".
Isothermal nucleic amplification
On 27 March 2020, the FDA issued an Emergency Use Authorization for a test by Abbott Laboratories, called ID Now COVID-19, that uses isothermal nucleic acid amplification technology instead of PCR. The assay amplifies a unique region of the virus's RdRp gene; the resulting copies are then detected with "fluorescently-labeled molecular beacons". The test kit uses the company's "toaster-size" ID Now device which costs $12,000-$15,000. The device can be used in laboratories or in patient care settings, and provides results in 13 minutes or less. As of 28 March 2020, there were 18,000 ID Now devices in the U.S. and Abbott began manufacturing for 50,000 test kits per day.
On 8 May 2020, the FDA granted the first Emergency Use Authorization for a COVID-19 antigen test: "Sofia 2 SARS Antigen FIA" by Quidel Corp. It is a lateral flow test which uses monoclonal antibodies to detect the virus's nucleocapsid (N) protein. The result of the test is read out by the company's Sofia 2 device using immunofluorescence. The test, simpler and cheaper but less accurate than available PCR tests, can be used in laboratories or in patient care settings and gives results in 15 minutes. A negative test result may occur if the level of antigen in a sample is below the detection limit of the test and should be confirmed with an RT-PCR test.
Serology (antibody) tests
As of 4 May, eleven tests had been approved for diagnosis in the United States, all under FDA Emergency Use Authorization (EUA). The tests are listed and described at the Johns Hopkins Center for Health Security. Other tests have been approved in other countries.
In the United States, as of 28 April, Quest Diagnostics made a COVID-19 antibody test available for purchase to the general public through the QuestDirect service. Cost of the test is approximately US$130. The test requires the individual to visit a Quest Diagnostics location for a blood draw. Results are available days later. An antibody test is also available through LabCorp.
A number of countries are beginning large scale surveys of their populations using these tests. A study in California conducted antibody testing in one county and estimated that the number of coronaviruses cases was between 2.5 and 4.2% of the population, or 50 to 85 times higher than the number of confirmed cases.
In late March 2020, a number of companies received European approvals for their test kits. The testing capacity is several hundred samples within hours. The antibodies are usually detectable 14 days after the onset of the infection.
WHO Emergency Use Listing
|Date listed||Product name||Manufacturer|
|3 April 2020||Cobas SARS-CoV-2 qualitative assay for use on the cobas 6800/8800 Systems||Roche Molecular Systems|
|7 April 2020||Coronavirus (COVID-19) genesig rtPCR assay||Primerdesign|
|9 April 2020||Abbott Realtime SARS-CoV-2||Abbott Molecular|
|24 April 2020||PerkinElmer SARS-CoV-2 Real-time RT-PCR Assay||SYM-BIO LiveScience|
As of 7 April 2020, the WHO had accepted two diagnostic tests for procurement under the Emergency Use Listing procedure (EUL) for use during the COVID‑19 pandemic, in order to increase access to quality-assured, accurate tests for the disease. Both in vitro diagnostics, the tests are genesig Real-Time PCR Coronavirus (COVID‑19) manufactured by Primerdesign, and cobas SARS-CoV-2 Qualitative assay for use on the cobas® 6800/8800 Systems by Roche Molecular Systems. Approval means these tests can also be supplied by the United Nations and other procurement agencies supporting the COVID‑19 response.[clarification needed]
|Samples from ...||Positive rate|
|Bronchoalveolar lavage fluid specimens||93% (n=14)|
|Nasal swabs||63% (n=5)|
|Fibrobronchoscope brush biopsy||46% (6/13)|
|Pharyngeal swabs||32% (n=126)|
RT-PCR is considered the gold standard of diagnosis for COVID-19 and other viruses. Although it has high sensitivity and specificity in a laboratory setting, in one study the sensitivity dropped to 66-88% clinically. Most experts believe improper sample collection, exemplified by failure to acquire enough sample and failure to insert a swab deep into the nose, are to blame for the low clinical sensitivity. The time course of infection also affects the accuracy, for being too late or too early to be tested can lead to a viral load that is too low to be detected, whereas RNA breakdown due to improper storage for too long time could also lead to wrong results. In one study a positive test result was highest at week one (100%), followed by 89.3%, 66.1%, 32.1%, 5.4% and zero by week six.
Early in March 2020, China has been reporting the problems with accuracy in their test kits. A paper published in JAMA researched the RT-PCR sensitivity for COVID-19 in 1070 samples from 205 Wuhan patients, shows a varied sensitivity according to the methods and location of sample collection, where samples from bronchoalveolar lavage fluid specimens tested with the highest sensitivity for COVID-19. The authors argued that CT scan shows a higher sensitivity for testing for COVID-19. Spain purchased test kits from Chinese firm Shenzhen Bioeasy Biotechnology Co Ltd, but found that results were inaccurate. The firm explained that the incorrect results may be a result of a failure to collect samples or use the kits correctly. The Spanish ministry said it will withdraw the kits that returned incorrect results, and would replace them with a different testing kit provided by Shenzhen Bioeasy.
Different test kits also shows inconsistent sensitivity. According to a Dutch CDC-led laboratory investigation comparing 7 PCR test kits from different countries, test kits made by BGI from Shenzhen, China, shows the highest sensitivity compared to the test kits from other countries. The test kits with the highest sensitivity, including those from R-Biopharm AG, BGI, KH Medical, and Seegene, are recommended to diagnose people with low viral loads, while all the other test kits are still satisfying when used for those routine diagnostics of symptomatic patients, according to the research. In the United States, the test kits developed by the CDC had "flaws;" the government then removed the bureaucratic barriers that had prevented private testing.
Isothermal nucleic amplification test
In a study conducted by the Cleveland Clinic, the ID Now COVID-19 test detected the virus in only 85.2% of the samples that contained it. According to the director of the study a test should be at least 95% reliable. Abbott said the issue could have been caused by storing the samples in a special solution instead of inserting them directly into the testing machine. Another study, by researchers at NYU Langone Medical Center, concluded that the machine was unacceptable in their clinical setting as it missed too many infections. The FDA announced on 14 May that they have received and are reviewing 15 adverse event reports about the Abbott ID Now device that suggest some users are receiving inaccurate negative results.
The test results from some of the FDA-authorized COVID-19 antibody tests can be viewed at the FDA website.
Antibody tests have a low positive predictive value (PPV) when the prevalence in the population of people with antibodies is low. For example, suppose there is a population in which 5% of the people have at some point been infected and so should test positive for antibodies. Select 100 people at random and administer an antibody test that has a specificity of 95%, meaning that 5 people who are actually negative will be expected to test positive. Since 5% of the people actually do have antibodies those five people will also test positive giving us 10 people testing positive, with an incorrect result being returned for half of them. So even though the specificity of the test is high, the PPV of the test in this population is only 50%. In this situation conducting a second independent test in sequence when the first test yields a positive result will increase the PPV to 94.5%, meaning that only about 5% of those testing positive would receive an incorrect result. If the prevalence of antibodies in the population is 52% a single such test will yield a PPV greater than 95%. In a low-prevalence setting the negative predictive value (NPV) of a test increases. The actual prevalence of SARS-CoV-2 antibody positive individuals in the U.S. population is not currently known. The test results at the FDA website list the PPV and NPV for each test assuming a prevalence of antibodies in the population of 5%.
Nearly two million antibody tests imported into Australia and costing $20 million were declared unusable. 80% of test kits for COVID-19 blood antibody that the Czech Republic purchased from China gave wrong results. Slovakia purchased 1.2 million antibody-based test kits from China which were found to be inaccurate. China accused the Czech Republic and Slovakia of incorrect use of antibody-based tests, after Slovakian Prime Minister said the kits should be "dumped into the Danube". Ateş Kara of the Turkish Health Ministry said the antibody-based test kits Turkey purchased from China had a "high error rate" and did not "put them into use". The UK purchased 3.5 million antibody test kits from China but in early April 2020 announced these were not usable. On 21 April 2020, the Indian Council of Medical Research (ICMR) has advised Indian states to stop using the rapid antibody test kits purchased from China after receiving complaints from one state. Rajasthan health minister Raghu Sharma on 21 April said the kits gave only 5.4 percent accurate results against the expectation of 90 percent accuracy. The Chinese embassy in India described the decision to oust Chinese test kits to be "unfair and irresponsible" and "look at issues with pre-emptive prejudice" when responding to ICMR's decision, and explained that antibody tests are only for "surveillance purposes".
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. Out of the sixteen reference laboratories, seven are in Asia, five in Europe, two in Africa, one in North America and one in Australia.
Testing, followed with quarantine of those who tested positive and tracing of those with whom the SARS-CoV-2 positive people had had contact, resulted in positive outcomes.[clarification needed].
Researchers working in the Italian town of Vò, the site of the first COVID‑19 death in Italy, conducted two rounds of testing on the entire population of about 3,400 people, about ten days apart. About half the people testing positive had no symptoms, and all discovered cases were quarantined. With travel to the commune restricted, this eliminated new infections completely.
Unlike other Asian countries, Japan did not have a pandemic of SARS or MERS, so the PCR testing system was not well equipped. That made Japan preferentially test patients with severe illness and those who were in close contact with infected people at the beginning. The Novel Coronavirus Expert Meeting chose the cluster measures to quickly detect and destroy clusters, a group of infected people. At the same time, the Expert Meeting analyzed the outbreak from Wuhan, which became the first wave of COVID-19 in Japan, and discovered the conditions under which clusters occur, so-called "Three C's" (Closed spaces, Crowded spaces and Close-contact settings), and asked the whole nation to avoid such sites. In January, contact tracers at public health centers across Japan took action shortly after the first infection was found. Since then, they have been tracking the movements of the disease. Only administrative tests were carried out at first, but PCR test was covered with insurance on March 6, and private companies began to test, and the test system was gradually expanded. On April 3, the people testing positive were legally permitted to recuperate at home or in a hotel if they had asymptomatic or mild illness, which solved the lack of beds. While succeeding in containing the first wave from China (identified in May by epidemiological survey of coronavirus genomic molecules), the second wave caused by returnees from Europe and the US occurred in mid-March, which led to the spread of infection in April. On April 7, Japan declared a state of emergency, which is not as strict as a lockdown because it is not legal in Japan to block cities or restrict outing. On May 13, COVID-19's Antigen Test Kits, which can check whether infected or not in in a little more than ten minutes although have low sensitivity, started to be covered by insurance, and was used in combination with PCR test for confirmed diagnosis. The number of PCR tests per 100,000 people in Japan is far smaller than in other countries although the positive rate is lower. Because of that, some pointed out that COVID-19 might be mixed in patients with pneumonia, but there were no pandemics and no excess mortality occurred until March. The Expert Meeting said, "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." Expert Meeting believe that it would be better to use CT scans data and doctor's findings to detect coronavirus, not just PCR tests, by the experiences such as the COVID-19 pandemic on Diamond Princess. In Diamond Princess, there were many cases in which the people testing negative later tested positive. On the other hand, half of coronavirus-positive who remained mild or asymptomatic had pneumonia findings on CT scans and their CT image showed a frosted glass shadow that is characteristic of the new coronavirus pneumonia.
With aggressive contact tracing, inbound travel restrictions, testing, and quarantining, the COVID-19 pandemic in Singapore has proceeded much more slowly than in other developed countries[dubious ], but without extreme restrictions like forced closure of restaurants and retail establishments. Many events have been cancelled, and Singapore advised residents to stay at home on 28 March, but schools reopened on time after holiday break on 23 March, even though schools did close moving to "full home-based learning" on 8 April.
On 27 April, Russia tested 3 million people and had 183,000 people under medical supervision because they were suspected of having the virus with 87,147 people having tested positive for the virus and total confirmed deaths at 794. On 28 April Anna Popova head of Federal Service for Surveillance in Healthcare (Roszdravnadzor) in a presidential update said there were now 506 laboratories testing; 45% of those tested positive had no symptoms; incidence of pneumonia reduced from 25% to 20%; and only 5% of patients had a severe form. 40% of infections were from family members. The speed of people reporting illness has improved from six days to the day people find symptoms. Antibody testing was carried out on 3,200 Moscow doctors and 20% have immunity.
U.S. aircraft carrier
After 94% of the 4,800 crew had been tested, roughly 60 percent of the 600-plus sailors who tested positive did not have symptoms. Sailors who test positive must spend at least two weeks in isolation and then test negative twice in a row, with the tests separated by at least a day. Five sailors who went through this process and had been admitted back onto the ship subsequently developed flu-like symptoms and again tested positive.
Several other countries, such as Iceland and South Korea, have also managed the pandemic with aggressive contact tracing, inbound travel restrictions, testing, and quarantining, but with less aggressive lock-downs. A statistical study has found that countries that have tested more, relative to the number of deaths, have much lower case fatality rates, probably because these countries are better able to detect those with only mild or no symptoms. A subsequent study has also found that countries that have tested more widely also have a younger age distribution of cases, relative to the wider population.
Research and development
A test which uses monoclonal antibodies which bind to the nucleocapsid protein (N protein) of the SARS-CoV-2 is being developed in Taiwan, with the hope that it can provide results in 15 to 20 minutes just like a rapid influenza test. The World Health Organization raised concerns on 8 April that these tests need to be validated for the disease and are in a research stage only. The United States Food and Drug Administration approved an antibody test on 2 April, but some researchers warn that such tests should not drive public health decisions unless the percentage of COVID‑19 survivors who are producing neutralizing antibodies is also known.
Virus testing statistics by country
The figures are influenced by the country's testing policy. If two countries are alike in every respect, including having the same spread of infection, and one of them has a shortage of testing capability, it may test only those showing symptoms while the other country having greater access to testing may test both those showing symptoms and others chosen at random. The country that tests only people showing symptoms will have a higher figure for "% (Confirmed cases as percentage of tested samples or tested cases)" than the country that also tests people chosen at random. If two countries are alike in every respect, including which people they test, the one that tests more people will have a higher "Confirmed / million people".
|%||Tested / |
|Confirmed / |
|Bosnia and Herzegovina||30 May||64,623||samples||2,494||3.9||18,887||729|||
|Burkina Faso||21 May||6,642||samples||814||12.3||318||39|||
|Costa Rica||23 May||22,910||samples||918||4.0||4,583||184|||
|DR Congo||5 May||2,256||705||31.3||25||7.9|||
|El Salvador||4 May||32,030||587||1.8||4,938||90|||
|Ivory Coast||25 May||18,303||2,423||13.2||694||92|||
|New Zealand||26 May||267,435||samples||1,154||0.43||53,663||232|||
|North Korea||17 April||740||cases||0||0||29||0|||
|North Macedonia||5 May||17,544||1,526||8.7||8,446||735|||
|Northern Cyprus[d]||23 May||31,005||108||0.35||95,107||331|||
|Saint Lucia||25 May||898||18||2.0||4,937||99|||
|Saudi Arabia||8 May||418,722||35,432||8.5||12,027||1,018|||
|South Africa||23 May||564,370||cases||21,343||3.8||9,602||363|||
|South Korea||27 May||846,296||cases||11,344||1.4||16,366||219|||
|Sri Lanka||24 May||53,092||cases||1,094||2.1||2,450||50|||
|Trinidad and Tobago||9 May||2,271||samples||116||5.1||1,665||85|||
|United Arab Emirates||22 May||1,924,234||27,892||1.4||200,455||2,906|||
|United Kingdom||30 May||4,171,408||samples||272,826||6.5||61,757||4,039|||
|United States||29 May||16,099,515||1,735,341||10.8||49,048||5,287|||
Virus testing statistics by country subdivision
|%||Tested / |
|Confirmed / |
|Australia||Australian Capital Territory||27 May||15,253||107||0.70||38,019||251|||
|Australia||New South Wales||27 May||464,351||3,089||0.67||57,402||382|||
|Australia||Northern Territory||22 May||7,369||29||0.39||29,971||118|||
|Australia||South Australia||27 May||91,597||440||0.48||52,291||251|||
|Australia||Western Australia||27 May||78,308||570||0.73||29,869||217|||
|Canada||British Columbia||29 May||141,392||2,562||1.8||27,665||501|||
|Canada||New Brunswick||29 May||24,169||128||0.53||30,986||164|||
|Canada||Newfoundland and Labrador||29 May||11,907||261||2.2||22,838||501|||
|Canada||Northwest Territories||29 May||2,171||5||0.23||48,348||111|||
|Canada||Nova Scotia||29 May||41,969||1,055||2.5||42,937||1,079|||
|Canada||Prince Edward Island||29 May||6,264||27||0.43||39,606||171|||
|China||Hong Kong||27 April||154,989||1,037||0.67||20,714||139|||
|China||Wuhan, Hubei||13 May||2,637,964||52,141||2.0||235,280||4,650|||
|India||Andaman and Nicobar Islands||29 May||7,567||33||0.44||19,060||83|||
|India||Andhra Pradesh||30 May||363,378||3,461||0.95||6,958||66|||
|India||Arunachal Pradesh||29 May||7,488||3||0.04||4,979||2.0|||
|India||Dadra and Nagar Haveli and Daman and Diu||25 May||17,871||70||0.02||12,643||2|||
|India||Himachal Pradesh||29 May||33,979||295||0.87||4,655||40|||
|India||Jammu and Kashmir||30 May||164,581||2,341||1.4||12,465||177|||
|India||Madhya Pradesh||30 May||161,552||7,891||4.9||1,965||96|||
|India||Tamil Nadu||30 May||479,155||21,184||4.4||6,330||280|||
|India||Uttar Pradesh||30 May||279,288||7,701||2.8||1,241||34|||
|India||West Bengal||30 May||194,397||5,130||2.6||2,006||53|||
|Italy||Aosta Valley||26 May||14,262||1,181||8.3||113,491||9,398|||
|Italy||Friuli-Venezia Giulia||26 May||121,412||3,251||2.7||99,909||2,675|||
|Italy||South Tyrol||26 May||61,464||2,593||4.2||115,306||4,864|||
|Russia||Moscow Oblast||26 May||366,201||35,163||9.6||47,615||4,572|||
|Russia||Nizhny Novgorod Oblast||27 May||213,409||8,735||4.1||65,974||2,700|||
|Russia||Saint Petersburg||27 May||732,701||14,463||2.0||135,734||2,679|||
|South Africa||Western Cape||23 May||114,869||12,947||11.3||16,783||1,892|||
|United Kingdom||Scotland||24 May||101,713||15,101||14.8||18,704||2,777|||
|United States||California||27 May||1,736,894||98,980||5.7||43,958||2,505|||
|United States||Florida||27 May||935,271||52,634||5.6||43,546||2,451|||
|United States||Illinois||26 May||786,794||113,195||14.4||62,090||8,933|||
|United States||Louisiana||27 May||347,647||38,467||11.1||74,782||8,281|||
|United States||Massachusetts||26 May||545,481||93,693||17.2||78,492||13,482|||
|United States||Michigan||26 May||495,416||55,104||11.1||49,440||5,499|||
|United States||New Jersey||27 May||660,325||156,628||23.7||74,343||17,634|||
|United States||New York||27 May||1,811,544||364,965||20.1||93,121||18,761|||
|United States||Texas||26 May||858,398||56,560||6.6||29,604||1,951|||
|United States||Washington||26 May||332,791||20,181||6.1||43,703||2,650|||
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- 1 Test methods
- 2 Infectivity
- 3 Minimum testing necessary
- 4 Approaches to testing
- 5 Production and volume
- 6 Available tests
- 7 Testing accuracy
- 8 Confirmatory testing
- 9 Clinical effectiveness
- 10 Research and development
- 11 Virus testing statistics by country
- 12 Virus testing statistics by country subdivision
- 13 References
- 14 External links