Key points
- People with signs or symptoms of COVID-19 should undergo diagnostic testing.
- Serial point-of-care screening can provide rapid results and be critical in identifying asymptomatic cases necessary to interrupt SARS-CoV-2 transmission. This is especially important when community risk or transmission levels are considerable or high.
- Selection and interpretation of SARS-CoV-2 tests should be based on the context in which they are used, including the prevalence of SARS-CoV-2 in the population being tested.
- Vaccination status should not affect the results of viral tests for SARS-CoV-2.
- This guide has been developed based on what is currently known about SARS-CoV-2 and COVID-19 infection and is subject to change as additional information becomes available.
A robust and responsive testing infrastructure is essential to our success in stopping the spread of SARS-CoV-2, the virus that causes COVID-19. This overview describes current information on the categories of tests used to detect SARS-CoV-2 infection and the strategies envisaged for the use of those tests, including diagnosing infections, screening in an effort to reduce asymptomatic transmission, or presymptomatic and trend monitoring. in infection.
This guide also includes considerations for:
- health equity in testing;
- choose a test;
- interpretation of the results of the SARS-CoV-2 test in vaccinated people;
- links to guidance for specific settings (K-12 schools, businesses, non-health workplaces, correctional and detention facilities);
- other considerations when deciding to try
This information is intended for use by healthcare providers and public health professionals and those who organize and implement tests in non-healthcare related settings such as schools, workplaces, and group housing. Information about SARS-CoV-2 testing is also available to the general public.
Considerations when testing
SARS-CoV-2 testing can be incorporated as part of a comprehensive approach to reducing transmission. Symptom detection, testing, and contact tracing are strategies to identify people infected with SARS-CoV-2 so that steps can be taken to slow and stop the spread of the virus.
People who undergo tests should be given clear information about:
- The manufacturer and name of the test, the type of test, the purpose of the test, the performance specifications of the test, any limitations associated with the test, who will pay for the test, how the test will be conducted, how and when people will receive the test results and;
- How to understand what the results mean, the actions associated with negative or positive results, the difference between workplace screening and medical diagnostic tests, who will receive the results, how the results can be used, and the consequences of refusing to submit to the test.
Vaccination test and SARS-CoV-2
Previous receipt of a COVID-19 vaccine should not affect the results of SARS-CoV-2 viral tests (nucleic acid amplification tests (NAAT) or antigen). Because the COVID-19 vaccines from Pfizer-BioNTech, Moderna and Johnson & Johnson use the SARS-CoV-2 spike protein to generate an immune response, a positive serological (antibody) test for the IgM / IgG spike protein could indicate a previous infection or vaccination.
Currently, antibody testing is not recommended to assess immunity to SARS-CoV-2 infection after vaccination with COVID-19 or to assess the need for vaccination in an unvaccinated person. To assess evidence of a prior infection in a vaccinated individual, an antibody test that specifically evaluates IgM / IgG against the nucleocapsid protein should be used (e.g., for public health surveillance or diagnosis of disease). Multisystemic inflammatory syndrome in children (MIS-C) Syndrome in adults (MIS-A)).
Testing for SARS-CoV-2 infection
Many categories of tests are used to detect SARS-CoV-2.1 and their performance characteristics vary.
- Some tests provide results quickly (in minutes); others take time to process.
- Some must be done in a laboratory by trained personnel, some can be done at the point of care, and some can be done at home or on the go.
- Some tests are very sensitive (ie few false-negative results or few missed SARS-CoV-2 detections); others are very specific (ie few false-positive results or few tests that incorrectly identify SARS-CoV-2 when the virus is not present); and some are sensitive and specific.
- Some tests can be done frequently because they are less expensive, easier to use, and supplies are readily available.
- The selection and interpretation of SARS-CoV-2 tests should be based on the context in which they are used, including the prevalence of SARS-CoV-2 in the population being evaluated (see Table 1) and the status (signs, symptoms, contacts) of the person being tested.