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COVID-19 Health Alert # 14:
Considerations for use of assays currently available for SARS-CoV-2 (COVID-19) testing
Bureau of Communicable Diseases, August 6, 2020
Summary
- Clinicians and public health officials should be aware of the availability of new platforms for COVID-19 testing, the appropriate use and potential limitations of each.
- At this time, three main categories of tests are available for use, molecular (PCR), antigen, and serologic (antibody) tests. Of these, only molecular and antigen tests are approved for diagnosis of acute COVID-19.
- At-home tests are now available and may be used in accordance with the specifications described in the FDA Emergency Use Authorization, which are explained in the package insert of these products.
Molecular and antigen tests are recommended to diagnose acute infection. Molecular (“PCR”) tests detect viral nucleic acids, and antigen tests detect viral proteins from respiratory specimens (e.g., nasal swabs).
- Some tests are point-of-care tests, meaning results may be available at the testing site in less than an hour.
- Other tests must be sent to a laboratory to analyze, a process that may take 1-2 days once received by the laboratory.
Serologic or antibody tests help determine whether a patient was previously infected—even if that person never showed symptoms. These tests detect patient antibodies in blood.
- An antibody test may not detect acute COVID-19 infection; it can take 1–3 weeks after infection for antibodies to be present.
- The Centers for Disease Control and Prevention (CDC) does not currently recommend using antibody testing as the sole basis for diagnosis of acute infection, and antibody tests are not authorized by the U.S. Food and Drug Administration (FDA) for such diagnostic purposes.
- In certain situations, serologic assays may be used to support clinical assessment in conjunction with viral detection tests (see CDC Interim Guidelines for COVID-19 Antibody Testing).
- There are other Human Coronaviruses that cause mild to moderate upper respiratory tract illnesses. COVID-19 antibody tests may cross-react with these seasonal Coronaviruses that are circulating in the population, although antibody tests with FDA Emergency Use Authorization (EUA) have shown good specificity and minimal cross-reaction.
At-Home Tests for COVID-19
At-home COVID-19 tests are currently available for purchase. They have been authorized by the FDA under EUA to diagnose active COVID-19 infections. The patient fills out an intake survey that is meant to prioritize the test for those who may have been exposed, are experiencing symptoms, or are part of a high-risk population. Test collection kits are mailed to patients after approval by medical personnel. Respiratory specimens (i.e. nasal swabs) are collected at home and mailed to specific laboratories for testing. Patients may receive results directly from that laboratory or from the company.
COVID-19 Testing Considerations
- Each COVID-19 test has different performance characteristics and instructions for use. The characteristics and instructions are documented in a package insert, which is available through the manufacturer, the laboratory performing the test, or the FDA website.
- Some tests with lower sensitivity require confirmatory testing of negative results by a second test method (preferably a molecular test); please see the package insert of the test being used.
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For at-home tests, patients should carefully follow all instructions for specimen collection, storage and transport.
- For some tests, the test performance has not been characterized for children. Check the package insert and test instructions.
- The specimen should be collected only from the patient for which the test was ordered.
- Test performance has not been characterized for animals.
- It is critical to carefully follow all the instructions for test use. Failure to follow test instructions could jeopardize performance of the test and lead to false results.
Reporting
COVID-19 remains a Category I Reportable Condition in Wisconsin, which means health care providers and/or laboratories must report confirmed or suspected cases to the Department of Health Services (DHS) within 24 hours of detection. In addition to COVID-19 test results, hospitalizations due to COVID-19 and deaths due to COVID-19 are required to be reported to DHS. Public health intervention is expected as indicated, see Wis. Admin Code. § DHS 145.04(3)(a) and Wis. Stat. § 252.05.
- DHS waived the requirement for notifying local health departments by telephone of suspected and confirmed cases, see COVID-19 Health Alert #4. Cases should be reported electronically through the Wisconsin Electronic Disease Surveillance System (WEDSS), or by fax to the patient’s local health department.
- If the patient resides in more than one state (i.e., secondary recreational residence), please report results to all states of residence.
- If a non-Wisconsin resident is temporarily visiting Wisconsin, please attempt to collect a local address and phone number. This information should be provided to the local health department where the patient is staying so public health follow-up can occur.
Resources
About the COVID-19 Health Alert Network
The content of this message is intended for public health and health care personnel and response partners who have a need to know the information to perform their duties. The HAN will be the primary method for sharing time-sensitive public health information with clinical partners during the COVID-19 response. Health care providers and other officials can subscribe and unsubscribe using their preferred email address at the DHS COVID-19 website.
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