When you have covid, here’s how you know you’re no longer contagious


There are no hard and fast rules as to how sick a person will become or how long a person will remain infectious.

Rapid home COVID-19 tests Jim Wilson/The New York Times

You have covid-19. When can we come out of isolation? If you resume your activities outside your home, can you be sure that you are no longer contagious?

It is complicated. Be warned: The Centers for Disease Control and Prevention guidelines are nuanced but a bit confusing.

These guidelines are under review and may change. Several infectious disease experts have said they believe covid patients should have a negative antigen test – which gives results within minutes – before being released from isolation. The CDC currently leaves this optional and does not explicitly recommend it.

The important thing to consider, experts say, is that each person and each case of covid is unique. There are no hard and fast rules as to how sick a person will become or how long a person will remain infectious. The guidelines provide a general framework, but patients should consider their different circumstances, priorities and resources when assessing risk.

Q: How long should I self-isolate if I have covid?

A: The coronavirus has the delicate particularity of being transmissible even before the infected person shows symptoms. In general, the peak period of virus shedding begins about a day or two before the onset of symptoms and continues two or three days after.

Even if a person is less likely to transmit the virus later in the illness, it is still possible. Research shows that people continue to shed viruses that can be grown in the lab – a good test of the virus’ transmission potential – for about eight days on average after testing positive.

Experts say it is highly unlikely that the virus will be transmitted after 10 days, even if a person still tests positive.

The CDC is asking patients to self-isolate for at least five days. On Day 6, you can end isolation as long as your symptoms have improved and you have been fever-free for at least 24 hours without taking fever medication. The CDC has a calculator on its Isolation and Quarantine webpage to help people figure this out.

A potentially confusing point: Day 1 of your isolation, according to the CDC, is the day after you begin to experience symptoms or test positive. (So ​​if you have a sore throat on Monday afternoon, that’s day 0 and Tuesday is day 1.)

Even if you test negative, wear a properly fitting mask until day 10 if you must be around other people at home or in public. Do not travel.

If you decide to take a rapid home test several days after your infection started, the best approach is to use it near the end of the five-day window, according to the CDC.

If positive after the five-day isolation period, you must continue to self-isolate for a full 10 days, per agency guidelines.

Q: Wait. Shouldn’t I test negative in a rapid test before leaving isolation?

A: The CDC guidelines on this are confusing. It does not explicitly recommend testing negative to end isolation.

But many experts believe rapid home tests, also known as antigen tests, should be used to break out of isolation.

That’s what happened with President Joe Biden, who tested negative twice before leaving solitary confinement. (Biden, who was taking the antiviral Paxlovid, suffered a “rebound” infection, testing positive on Saturday, and returned to isolation.) Additionally, experts point out that rapid tests are more readily available than last December, when the CDC has published these guidelines.

“Given that a significant portion of people have a rapid positive test after 5 days, I think an updated recommendation should include people who have a rapid negative test before coming out of isolation for COVID,” Tom Inglesby , director of the Johns Hopkins Center for Health Security, said in an email. He served as the Biden administration’s senior testing adviser from December to April.

“A negative antigen test is pretty reassuring that you can no longer pass the infection on to other people,” said Amy Barczak, an infectious disease expert at Massachusetts General Hospital who has studied how long covid patients can shed the virus. In a recent study published in the New England Journal of Medicine, she and her colleagues found that, on average, people infected with the omicron variant of the virus can shed virus that can be cultured in the lab for eight days.

Q: Should I repeat the rapid test if it is negative?

A: Barczak says that for healthy people, if you test negative on a rapid antigen test on or after day 5, “you are unlikely to be infectious to other people.”

For people particularly concerned about transmitting the virus, further testing is not a bad idea. In symptomatic people, clinicians sometimes recommend a second rapid test to be sure. Biden, for example, tested negative Tuesday evening, and again Wednesday morning, before leaving solitary confinement.

Michael Mina, a former Harvard University infectious disease epidemiologist and immunologist who is an expert in rapid tests, said two tests 24 hours apart could provide additional security, like a double lock on your door. If people have access to testing, then “two tests in a row is just better form, better protection, than one negative test.”

Q: When should you take a PCR test versus a rapid home test?

A: PCR tests, a type of molecular test, look for the genetic material of the virus. They can detect even the smallest amounts of virus, before you have enough in your body to pass it on to other people. They’re more useful at first as a confirmatory test to see if you’re sick with covid but aren’t useful for determining if you’re contagious to others, said Albert Ko, an epidemiologist and infectious disease physician at the University of Yale.

If you develop covid-like symptoms, the CDC recommends that you get tested immediately. A negative PCR test in a symptomatic person means that you are very unlikely to have covid.

If you have been in close contact with someone with covid and then tested negative with a rapid test, you may want to get extra assurance that you are not infected. In that case, you can take a PCR test, Ko said. Most PCR tests need to be analyzed by a lab, and the results can take a few days.

A PCR test after being sick isn’t really practical, because “for the average healthy person, the PCR test is going to stay positive longer than it’s actually infectious,” says Barczak.

Rapid antigen tests are more convenient than PCR tests to quickly determine if you are capable of transmitting the virus. If you are symptomatic, an antigen test will be more reliable, as your body emits a lot more virus to detect. But even without symptoms, people can test positive in a rapid antigen test and pose a risk to others. Most home tests provide results in 10 to 15 minutes using samples taken with a nasal swab.

Since rapid tests provide results quickly and are essentially tests for contagiousness, people should use them – even if they feel well and have no symptoms – just before planning to attend indoor events or at large gatherings, especially if they expect to be around people who are more vulnerable to covid, including those with weakened immune systems or those at higher risk of infection.


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