Sorry, but a negative test does not give you a green light for Thanksgiving.

This yr, as they put together to let turkeys brine and pie crusts thaw, folks throughout the nation are ready for one thing additional: a coronavirus test they hope can clear them to mingle with family members.

Because a optimistic test filters out individuals who ought to undoubtedly not be out with others, many individuals take into account a negative coronavirus test to be a ticket to freely socialize with out precautions. But scientists and docs say this is dangerously misguided.

The major cause is that a test offers details about the extent of the virus on the time of the test. An individual might be contaminated but not have sufficient virus for it to register but. Or, a individual might turn out to be contaminated within the hours or days after taking a test. Also, the exams do not have 100 p.c accuracy.

“If you require all of your guests to email you a negative test result before your Thanksgiving dinner, it will definitely decrease the risk of an outbreak — but not completely,” mentioned Dr. KJ Seung, chief of technique and coverage for the Covid response at Partners in Health. Yet that is a widespread misperception contact tracers hear when speaking to folks, he mentioned.

Laboratory exams that depend on a method known as polymerase chain response, or P.C.R., can detect the virus when it’s current even at very low ranges. But it would take a couple of days to return outcomes, leaving time for somebody to be uncovered.

Antigen exams are quicker, inexpensive and extra handy — they’ll ship leads to a matter of minutes — but are additionally extra vulnerable to lacking the virus when it’s scarce. And that might give somebody a false sense of safety en path to Thanksgiving dinner, mentioned Paige Larkin, a scientific microbiologist at NorthShore University HealthSystem in Chicago, the place she focuses on infectious illness diagnostics.

“A negative result is a snapshot in time,” Dr. Larkin mentioned. “It’s telling you that, at that exact second you are tested, the virus was not detected. It does not mean you’re not infected.”

In abstract, as Dr. Esther Choo, an emergency drugs doctor and a professor at Oregon Health and Science University, put it: “Testing negative basically changes nothing about behavior. It still means wear a mask, distance, avoid indoors if you can.”

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