As fall temperatures set in, cold and flu season gets into full swing and holiday travel picks up, people will undoubtedly have questions about COVID-19 testing. Is this the year people can finally return to large gatherings for traditional celebrations? What role does testing play when deciding whether to go out or stay home?
Adding to the confusion are personal accounts of people who are experiencing confusing or seemingly contradictory test results.
We are part of a team that has developed and tested SARS-CoV-2 tests since the early days of the pandemic. Additionally, some of us are infectious disease specialists with decades of experience.
Our insights from both the cutting edge of rapid testing research as well as our clinical perspectives from working directly with patients can help people figure out how to make the best use of rapid tests.
SARS-CoV-2, the virus that causes COVID-19, takes time to build up in the body, like many other viruses and bacteria that cause respiratory illness. Typically it takes two to three days to test positive after exposure. Our research group has demonstrated this, as have others.
Rapid tests detect parts of the virus that are present in the sample collected from your nose or mouth. If the virus has not replicated to a high enough level in that part of your body, a test will be negative. Only when the amount of virus is high enough will a person’s test become positive. For most omicron variants in circulation today, this is one to three days, depending on the initial amount of virus you get exposed to.
It’s important to clarify which type of test we’re talking about in this situation. Studies have shown that some people can test positive for a month or more with a PCR test. The reason for this is twofold: PCR tests are capable of detecting extremely small amounts of genetic material, and fragments of the virus can remain in the respiratory system for a long time before being cleared.
When it comes to rapid tests, there are reports that some people test positive for an extended period of time with the current strains of the omicron variant compared with earlier variants. Several studies show that most people no longer test positive after five to seven days from their first positive test, but between 10% to 20% of people continue to test positive for 10 to 14 days.
But why it takes longer for some people to clear the virus than others is still unknown. Possible explanations include a person’s vaccination status or the ability of one’s immune system to clear the virus.
In addition, a small number of people who have been treated with the oral antiviral drug Paxlovid have tested negative on rapid antigen tests, with no symptoms, only to “rebound” seven to 14 days after their initial positive test. In these cases, people sometimes experience recurring or even occasionally worse symptoms than they had before, along with positive rapid test results. People who experience this should isolate again, as it has been shown that people with rebound cases can transmit the virus to others.
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