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the-margin:-the-coronavirus-may-remain-in-the-body-for-a-month-or-more-—-but-does-that-mean-you’re-still-contagious?
the-margin:-the-coronavirus-may-remain-in-the-body-for-a-month-or-more-—-but-does-that-mean-you’re-still-contagious?

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The Margin: The coronavirus may remain in the body for a month or more — but does that mean you’re still contagious?

The Margin

New research suggests COVID-19 patients should be tested again four weeks after symptoms first appear


MarketWatch photo illustration/Getty Images, iStockphoto

Health experts are learning that recovering from the coronavirus takes time.

In fact, a new study of roughly 4,500 Italian COVID-19 patients published on Wednesday evening found that it takes 30 days on average for SARS-CoV-2, the novel coronavirus that causes the COVID-19 infection, to leave the body after the first positive test result. It takes 36 days on average for the virus to clear the body after a person starts showing symptoms. And it can linger even longer in older patients and in those with more severe illness, according to the peer-reviewed manuscript published in the online journal BMJ Open.

While it’s not clear from just this observational report whether someone is still infectious during this 30-or-so-day window, the authors recommend that patients testing positive for COVID-19 get tested again in four or more weeks after their symptoms first appear in order to minimize the risk of spreading the virus.


The study authors fear that COVID-19 patients are at risk of “unwittingly passing on the infection” as they return to work or school believing that they are all better.

Indeed, the long-term effects of COVID-19 are only just beginning to come to light, roughly half a year into the pandemic. Some “long hauler” coronavirus patients have continued to suffer symptoms and coronavirus-related health issues for months after their initial infections, including shortness of breath, extreme muscle weakness and fatigue, and brain fog. The CDC has warned that one in five previously healthy young adults weren’t back to their usual health 14 to 21 days after testing positive. And another study found more than half (55%) of coronavirus patients still had neurological problems three months later.

Read more:A lung doctor on what she’s learning about coronavirus ‘long haulers’: shortness of breath, fatigue, and depression but also ‘improvement over time’

What’s more, this new BMJ Open report also found that the rate of false negative test results appeared to be high early in the coronavirus patients’ recovery. The study subjects were tested 15 days after their first positive swabs, 14 days after their second swabs, and nine days after their third. Those who tested negative were tested again — and the negative results were only confirmed in 79% of those cases, suggesting a rate of one false negative out of every five negative test results.

The authors fear that the high rate of false negatives, plus the evidence that the virus remains in the body for more than a month, puts COVID-19 patients at risk of “unwittingly passing on the infection” as they return to work or school believing that they are all better.

Related:As schools reopen amid COVID-19 pandemic, how long do asymptomatic children remain contagious?

But the current guidance from the World Health Organization and the Centers for Disease Control and Prevention suggests that most COVID-19 patients are indeed in the clear after isolating themselves for 10 to 13 days. And those with mild to moderate illness, whose symptoms have resolved, can then leave quarantine without even getting tested for COVID-19 again.


The amount of virus a person is carrying, or their viral load, may be too low for that person to be contagious.

The CDC did not immediately respond to a MarketWatch request for comment about whether it has considered extending the length of time that COVID-19 patients should isolate themselves, or whether testing guidelines should be adjusted. The WHO notes that while some research has suggested that patients whose symptoms have resolved may indeed still test positive for COVID-19 for many weeks afterward, “these patients are not likely to be infectious and therefore are unlikely to be able to transmit the virus to another person.”

That’s because the amount of virus a person is carrying, or their viral load, may be too low for that person to be contagious. In fact, a recent New York Times analysis suggests that many people getting diagnosed with COVID-19 could be carrying “relatively insignificant amounts” of the virus, which means that they are probably not contagious. This is because the most widely used diagnostic COVID-19 tests are PCR tests that detect the presence of the virus’ genetic material in the body. And these sensitive diagnostics can flag not only live virus samples in the body, but also genetic fragments left over from an earlier infection. (These traces are kind of like how strands of a person’s hair or skin cells can be found in a room after the person is long gone.)

That’s not to say these standard diagnostic tests should be thrown out the window for being too sensitive, however. The Food and Drug Administration told the Times that when people are first infected with COVID-19, for example, they may also carry a low viral load. And tests that are less sensitive could miss these cases. The CDC also notes that someone could test negative for COVID-19 early in their infection.

Research suggests that the most contagious window for COVID-19 tends to be between one to three days before someone shows symptoms (with the highest viral loads on the day someone becomes symptomatic), up until about five days afterward, according to the World Health Organization. And this level of contagiousness appears to be one to two weeks for asymptomatic persons, and up to three weeks or more for patients with mild to moderate disease.

Related: This is when people with COVID-19 are at their most contagious

The bottom line: This is still a new virus, and health experts are still learning about how it spreads. People may be carrying the virus in their bodies longer than researchers first suspected, but it’s unclear exactly how long they will be contagious. A new study published in JAMA Pediatrics suggests that children, including asymptomatic ones, may shed the virus for weeks.

So what should people take from the latest research? They should keep practicing key social-distancing measures, monitoring for symptoms, and they should get tested if they start showing symptoms or suspect that they have been exposed. Even those who test negative — either because they haven’t been exposed to the virus, or because they have recovered from it — should continue taking steps to protect themselves and those around them. This includes: washing their hands often; avoiding close contact with people outside of their household by staying at least six feet apart; and covering their nose and mouth with a face mask around others, even if they don’t feel sick.

There were 25.8 million confirmed cases of COVID-19 worldwide as of Wednesday afternoon, according to the Johns Hopkins data, and at least 857,877 people have died. More than 17 million people are confirmed to have tested positive and recovered.

Follow more of MarketWatch’s coronavirus coverage here.

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