COVID-19 is a respiratory illness with symptoms ranging from mild to severe. Testing helps individuals understand their infection status and take precautions. Understanding when and why retesting is recommended can limit transmission and guide personal health decisions.
When to Retest After a Positive COVID-19 Result
After a positive COVID-19 test, retesting helps determine when isolation can end. If symptoms are improving and a person has been fever-free for at least 24 hours without fever-reducing medication, they may retest with an antigen test on day 5 or later. Day 0 is the day symptoms began or the date of the positive test if asymptomatic. If this test is negative, isolation can end, though continued masking around others until day 10 is advised.
Should the day 5 antigen test remain positive, it is recommended to continue isolation and retest every 24 to 48 hours. Isolation can end upon receiving a negative antigen test result. If an antigen test continues to be positive, isolation should continue for a full 10 days from the initial positive test or symptom onset. A positive antigen test result suggests active contagiousness, as these tests detect viral proteins indicating a higher viral load.
Conversely, a Polymerase Chain Reaction (PCR) test can remain positive for weeks or months after an initial infection. PCR tests are highly sensitive, detecting residual viral genetic material even when a person is no longer infectious. A positive PCR test alone is not a reliable indicator of current contagiousness after a recent infection. The Centers for Disease Control and Prevention (CDC) does not recommend retesting with a PCR test within 90 days of a positive result unless new symptoms appear.
When to Retest After COVID-19 Exposure
If you have been exposed to someone with COVID-19 but do not have symptoms, wait at least 5 full days after the last exposure before testing. Testing too early can lead to an inaccurate result, potentially yielding a false negative. The average incubation period for COVID-19 is between 5 and 7 days.
Even if the initial test after exposure is negative, repeat testing is important to reduce the risk of missing an infection. The Food and Drug Administration (FDA) recommends retesting at least 48 hours after a first negative antigen test, and then again 48 hours after a second negative test, for a total of three tests over five days, especially if no symptoms are present. If symptoms develop at any point after exposure, test immediately, regardless of the prior testing schedule.
When to Retest for New or Worsening Symptoms
Retesting is important if new or worsening symptoms consistent with COVID-19 appear, especially if they follow a period of improvement or a previous negative test. Symptoms like fever, cough, or fatigue warrant immediate retesting to determine a new infection or resurgence.
COVID rebound can occur, where symptoms return or a person tests positive again after initial recovery. This can happen whether or not antiviral medications, such as Paxlovid, were taken. If rebound symptoms appear and a test is positive, restart isolation from day 0 of the new symptoms.
Rebound symptoms are usually mild and resolve within a few days. While retesting is not universally recommended by the CDC for everyone after Paxlovid, if symptoms recur and a test is positive, it indicates a person may again be contagious. This necessitates renewed precautions to prevent further transmission.
Types of COVID-19 Tests and Retesting
Two main types of COVID-19 tests are used for retesting: rapid antigen tests and PCR tests. Rapid antigen tests detect specific viral proteins, known as antigens, found on the surface of the SARS-CoV-2 virus. These tests are quicker, providing results within minutes. They are most effective at identifying active infections when viral load is high, indicating current contagiousness. A positive rapid antigen test is highly reliable for indicating an active infection.
PCR (Polymerase Chain Reaction) tests, also known as molecular tests, work by detecting the genetic material (RNA) of the SARS-CoV-2 virus. These tests are highly sensitive and can detect small traces of viral RNA, amplifying them to detectable levels. While PCR tests are highly accurate for diagnosing an infection, they can remain positive for weeks or months after a person is no longer infectious. This is because they can pick up viral fragments that do not indicate active, transmissible virus.
The choice of test for retesting depends on the specific situation. Antigen tests are preferred for assessing current contagiousness and guiding isolation decisions. PCR tests are more suitable for confirming an initial infection, but their prolonged positivity makes them less useful for determining when a person is no longer able to spread the virus. Understanding these differences helps interpret retest results and guide health decisions.