Even after the fever has broken, the runny nose has dried up, the official five-day quarantine period has ended and the 10-day precautionary phase is over, some people are still testing positive for Covid — despite feeling totally fine.

If you find yourself in this situation, you might be puzzled over what to do, particularly since the Centers for Disease Control and Prevention offers little specific guidance on this front. It's difficult to know exactly how many people this affects — most people self-test at home, so their results are untracked — but a pre-vaccine study of Florida school children in 2020 found that 8.2% of high school kids still tested positive 9-14 days after their first positive tests.

Even small percentages can affect millions of people, as the country's total case count continues to rise: The U.S. has surpassed 85.7 million total Covid cases since the pandemic began, according to data from Johns Hopkins University, likely an undercount due to those at-home tests.

Here's what you need to know about the phenomenon, and what to do if it happens to you:

What you should do if you keep testing positive after 10 days

Testing positive for Covid doesn't necessarily mean that you're contagious. Rapid tests detect certain protein pieces of the virus, but those proteins alone don't cause infection. The same goes for PCR tests, which identify the virus' genetic material in your system.

So, to work out if positive tests mean people are infectious, scientists culture samples from these tests in petri dishes to see if more virus can grow, indicating that it's still alive and contagious. A recent Boston University study, which has yet to be peer-reviewed, used this technique and found that just 17% of people were likely still contagious six days after their first positive tests.

Unfortunately, there's currently no way to know which category you're in. But most experts say that as long as your symptoms are gone, you probably don't need to isolate anymore.

The CDC recommends isolating for five days after you first test positive, and ending your quarantine as long as you've been fever-free for 24 hours and your symptoms are improving. The agency's guidance adds that you should keep wearing a mask through day 10 — essentially a precaution in case you're still contagious.

Dr. Monica Gandhi, an infectious disease specialist at the University of California, San Francisco, says she'd "feel really comfortable" with a symptom-free person emerging after five days of isolation, even if they're still testing positive for Covid.

"Follow CDC guidance and wear a mask for the following five days," she says.

Dr. Wilbur Lam, a pediatrics and biomedical engineering professor who led Emory University's initiative to test Covid-19 diagnostics for the U.S. government, particularly recommends avoiding contact with people who may have compromised immune systems, or wearing a mask if you can't avoid the risk.

"Scientists, including our own center, are really trying to figure out what the variables are that may affect why one becomes persistently positive on rapid tests, and what the implications are both from a biological and a public health standpoint," he says.

What testing positive for more than 10 days could mean for your long-term health

Last month, the CDC issued an alarming warning that as many as one in five adult COVID-19 survivors may develop long Covid, potentially including long-term symptoms from fatigue and brain fog to circulation and digestive issues. Women, older people and those with chronic health conditions all appear to be at higher risk.

Covid isn't the only pathogen that can cause such issues: Dr. Jeremy Kamil, a virologist at Louisiana State University Health Shreveport, notes that other viruses, like human papillomaviruses, can also wreak havoc on the body weeks or even years after the initial infection.

More than 10 days of positive tests are not a known risk factor for long Covid, but they do raise questions about where the virus could linger. Some viruses are known to hide in tissues that don't produce symptoms — like fat cells or the gut, for example — before reemerging once it thinks the coast is clear.

Incidentally, this is one theory for why some people test positive for Covid beyond 10 days — but for now, it's just a theory. Experts stress that if you do keep testing positive after your week-and-a-half stint is over, you probably don't need to worry: The precautions are important to take, but you're unlikely to harm yourself or those around you by ending your isolation.

That'll remain true unless further research proves otherwise.

"I would just say, we just don't know enough to even be concerned," says Lam. "There's so many things to worry about in your life, this doesn't have to be one of them."

Correction: This story has been corrected to reflect Dr. Jeremy Kamil's affiliation with Louisiana State University Health Shreveport.

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