covid-19 testing covid-19 testing 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. 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. they are less useful for diagnosing current infections because antibodies may not develop for weeks after infection. it is used to assess disease prevalence, which aids the estimation of the infection fatality rate. part of a series on thecovid-19 pandemicscientifically accurate atomic model of the external structure of sars-cov-2. each "ball" is an atom. covid-19 (disease) sars-cov-2 (virus) cases deaths timeline 2019 2020 january responses february responses march responses april responses may responses june responses july responses august responses september responses october responses november responses december responses 2021 january responses february responses march responses april responses may responses june responses july responses august responses september responses october responses november responses december responses 2022 january responses february responses march responses april responses may responses june responses july responses august responses september responses october responses november december 2023 january february march april may locations by country and territory africa antarctica asia europe north america oceania south america by conveyance cruise ships naval ships international response endemic phase evacuations face masks international aid investigations into origin lockdowns by country misinformation by governments fake treatments social distancing software travel united nations world health organization wto ip waiver undercounting of deaths covid-19 apps zero-covid national responses africa china european union germany ghana india ireland netherlands new zealand nigeria philippines russia sweden uk government us federal government vietnam medical response disease testing breathalyzer development drug development drug repurposing public health mitigation vaccines history research vitt deployment authorizations operation warp speed misinformation and hesitancy us vaccine card vaccine passports current vaccines coronavac covaxin convidecia janssen medigen moderna novavax oxford–astrazeneca pfizer–biontech sinopharm bibp sputnik v variants variants of concern alpha beta gamma delta omicron other variants epsilon zeta eta theta iota kappa lambda mu cluster 5 lineage b.1.617 economic impact and recession arts and culture aviation cannabis cinema films disney fashion financial markets food industry food security journalism music performing arts retail shipping television us sportscasting programs tourism video games by country canada india ireland malaysia new zealand russia uk us by sport association football baseball basketball combat sports cricket disc golf gaelic games gridiron football ice hockey motorsport rugby league impacts animals black people crime death rates by country disability domestic violence emergency evacuations education female environment hospitals language lgbt community long-term care media coverage mental health symptoms migration military notable deaths other health issues politics diplomacy popular culture protests pregnancy prisons religion catholic church hajj science and technology social media strikes suicides telehealth xenophobia and racism society ireland malaysia new zealand russia uk us covid-19 portal 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. this variation has likely significantly impacted reported statistics, including case and test numbers, case fatality rates and case demographics. 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. 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. methods explanation of the underlying pathophysiology pertaining to diagnosis of covid-19 positive viral tests indicate a current infection, while positive antibody tests indicate a prior infection. other techniques include a ct scan, checking for elevated body temperature, checking for low blood oxygen level, and detection by trained dogs. 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. other methods used in molecular tests include crispr, isothermal nucleic acid amplification, digital polymerase chain reaction, microarray analysis, and next-generation sequencing. 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 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. rt-pcr can thereby detect sars-cov-2, which contains only rna. the rt-pcr process generally requires a few hours. these tests are also referred to as molecular or genetic assays. real-time pcr (qpcr) provides advantages including automation, higher-throughput and more reliable instrumentation. it has become the preferred method. the combined technique has been described as real-time rt-pcr or quantitative rt-pcr and is sometimes abbreviated qrt-pcr, rrt-pcr or rt-qpcr, 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, 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%. 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), throat swabs, deep airway material collected via suction catheter or 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." 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. 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. collecting saliva may be as effective as nasal and throat swabs, although this is not certain. sampling saliva may reduce the risk for health care professionals by eliminating close physical interaction. it is also more comfortable for the patient. quarantined people can collect their own samples. a saliva test's diagnostic value depends on sample site (deep throat, oral cavity, or salivary glands). some studies have found that saliva yielded greater sensitivity and consistency when compared with swab samples. 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. 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. viral burden measured in upper respiratory specimens declines after symptom onset. 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. no clear correlation has been described between length of illness and duration of post-recovery shedding of viral rna in upper respiratory specimens. demonstration of a nasopharyngeal swab for covid-19 testing demonstration of a throat swab for covid-19 testing a pcr machine 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. 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. the test amplifies rna directly, without the rna-to-dna conversion step of rt-pcr. 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. 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. 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. antigen tests can be performed on nasopharyngeal, nasal swab, or saliva specimens. antigen tests that can identify sars-cov-2 offer a faster and less expensive method to test for the virus. antigen tests are generally less sensitive than real-time reverse transcription polymerase chain reaction (rt-pcr) and other nucleic acid amplification tests (naats). antigen tests may be one way to scale up testing to much greater levels. 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. "there will never be the ability on a 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." 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). 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. swabs of respiratory viruses often lack enough antigen material to be detectable. this is especially true for asymptomatic patients who have little if any nasal discharge. viral proteins are not amplified in an antigen test. 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. 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. while some scientists doubt whether an antigen test can