After contracting Covid-19, some individuals may continue to test positive for the virus after symptoms resolve and isolation periods end. But are these individuals still contagious?

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For how long can you test positive?

According to Stephen Kissler, a postdoctoral fellow at the Harvard T.H. Chan School of Public Health, people tend to test positive on rapid Covid-19 tests for six to 10 days. However, outliers may test positive for longer.

Kissler said some individuals can test positive with rapid tests for up to 14 days, and, according to Alberto Paniz-Mondolfi, an associate professor at the Icahn School of Medicine at Mount Sinai, even longer with PCR tests.

"You can still have positivity that may persist for weeks and even months," Paniz-Mondolfi explained, noting that positive tests on PCR have been recorded for up to 60 days.

According to Benjamin tenOever, a microbiologist at the NYU Grossman School of Medicine, some people may continue to test positive because the weakened virus keeps replicating, or because of broken virus genomes.

Typically, the omicron variant stays localized in the upper respiratory tract, especially in individuals who have been vaccinated and boosted. As a result, there may be more nucleocapsid protein in the back of the throat and nose. In addition, broken virus genomes can linger after the virus creates a "bad version" of itself, said tenOever.

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How long should you isolate?

Last month, CDC reduced its Covid-19 isolation guidelines for people who test positive for Covid-19 to five days. After those five days, CDC said, "[i]f you have no symptoms or your symptoms are resolving … you can leave your house." 

Many health experts pushed back on the guidelines, arguing that the shortened isolation period without producing a negative test could lead to more coronavirus transmission. According to CDC, its updated guidelines were based on data that suggested most transmission "occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after."

In response to criticism, CDC defended its updated guidelines, and ultimately recommended that those who have access to a Covid-19 test and want to take one should take an antigen test near the end of their five-day quarantine. If their antigen test is positive, CDC said the infected person should keep quarantining until day 10. If the test comes back negative, the guidelines say the person is able to end isolation at day five but should continue wearing a well-fitting mask for an additional five days around people at home and in public.

So, what if an individual tests positive and quarantines until day 10, but then continues to test positive past the recommended isolation period?

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As CDC noted in its updated guidance, people tend to be most infectious towards the beginning of a Covid-19 infection. So, by the time you reach day eight, nine, or 10, "you still have the chance to spread to other people, but it's probably not as much as you did early in the course of your infection," Kissler said.

"If you are testing antigen positive, you should assume a low level of virus infection," tenOever said. "You are possibly transmissible."

And while experts say it's safest for individuals to continue to isolate until they no longer test positive, they note that this might not be feasible for everyone.

"You might be able to begin slowly sort of reintegrating while still being mindful of your contact," Kissler said. He recommended avoiding enclosed spaces with other people and wearing a mask, preferably something like a KN95 or KF94, USA Today reports.

Separately, Paniz-Mondolfi agreed, saying after 10 days, "you're good to go and you're even better to go if you keep practicing containment measures. Keep wearing your mask. Keep practicing social distancing." (Henderson, MedPage Today, 1/20; Jacoby, USA Today, 1/18)