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Here’s why a negative COVID-19 test doesn’t guarantee you can safely gather on Thanksgiving

People took COVID-19 tests at a drive-thru site in Fitchburg in November.
People took COVID-19 tests at a drive-thru site in Fitchburg in November.Jim Davis/Globe Staff

If you’re planning on relying on a COVID-19 test as the go-ahead before spending Thanksgiving with people from other households, experts say that doesn’t necessarily ensure the virus won’t spread.

“A test is just one point in time,” said Dr. Helen Boucher, chief of infectious diseases at Tufts Medical Center. “The incubation period for this virus is 14 days. Just because someone tests negative today doesn’t mean they won’t be positive tomorrow or in the next 13 days.”

A Thanksgiving dinner in which people from different households are sitting closely together indoors, not wearing masks, eating and drinking, particularly during the winter “where the virus likes to be” can create a “perfect storm,” Boucher said.

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It is clear that the virus is spreading in Massachusetts in little clusters in people’s homes, Boucher added, and eating together with other people from different households is a “high-risk activity with regard to COVID.”

Eleanor Murray, an assistant professor of epidemiology at Boston University, said a negative test ahead of a Thanksgiving gathering can mean a number of different things.

“It can mean at the time you got the test you were not infected,” Murray said. “But if that is three days before your gathering, that’s three days where you could become infected.”

It could also mean that a person is infected at the time of the test, but their viral load, or the amount of the virus in their system at the time, isn’t high enough to be detected yet, which would be “the worst case scenario,” Murray said. Someone who tests negative ahead of their gathering could also become infected at some point, which is why it’s important for people to still take precautions, like wearing a mask and practicing social distancing, even with a negative test result.

An event like Thanksgiving dinner can also be risky because families and friends like to have animated conversations, and “any kind of discussion with laughter or raised voices, those things can really project respiratory droplets,” which is how the virus can spread.

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Quarantining for as long as possible ahead of Thanksgiving is a good idea, and taking a test as late as possible in the quarantine process is helpful, but not perfect, said said Dr. Mark Siedner, an epidemiologist at Massachusetts General Hospital and associate professor of medicine at Harvard Medical School.

There are a number of things people can do to minimize the risk of spreading the virus if they’re still planning to gather with others, though the safest option would be not to see people who don’t live with you at all — and to avoid traveling, Siedner said.

“This is a time that the epidemic is spiraling out of control,” Siedner said. “Having 100 million people travel home over the holidays and start mixing with high-risk groups of people is a recipe for disaster that we want to try to avoid.”

If people do decide to travel for Thanksgiving, driving in a car alone poses the least risk of COVID-19 transmission, Siedner said, and for those planning to drive with others, they should wear a mask while in the car.

Inviting fewer people to attend, holding the event outdoors or with open windows for ventilation, wearing masks, and shortening the duration of the event are ways to minimize risk of spreading the virus at Thanksgiving, Murray said. Members of the same household eating together in rooms separate from others and wearing masks while spending time with other people would also help.

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She also encouraged people who are seeing others at Thanksgiving to stay home a few days after.

“If you’re going to do Thanksgiving dinner, don’t do Black Friday shopping,” Murray added. “Making sure you’re not going to transmit the infection onwards is really important.”

The Centers for Disease Control and Prevention has also issued a number of recommendations for minimizing the risk of COVID-19 before and during Thanksgiving events.

On Thursday, Governor Charlie Baker urged people to celebrate Thanksgiving in person with people from their households, cautioning that a large, traditional holiday gathering is “exactly the type of activity” that will increase the risk of COVID-19 transmission.

“Today we’re asking everybody to make a different choice this Thanksgiving,” Baker said.

Despite the difficult message of not being able to hold a traditional Thanksgiving holiday with family and friends, Boucher said there is reason to remain optimistic.

“We all should be really hopeful that if we can get through the next 8 to 12 weeks on the other side, there’s a lot of reason for hope,” she said. “There’s more therapies, more reasons to believe that by 2021, we’ll be in a better place. And the way to do that is to protect our vulnerable relatives and friends.”


Amanda Kaufman can be reached at amanda.kaufman@globe.com. Follow her on Twitter @amandakauf1.