Thanksgiving get-together? Virus spread possible even after testing negative

Coronavirus

(NEXSTAR) — As families plan for Thanksgiving, public health officials are warning against in-person gatherings even if you’ve had a negative coronavirus test.

“The coronavirus affects people differently. Some people have no symptoms at all and may not even know they are ill, even though they can transmit the coronavirus to others,” said Lisa Maragakis, M.D., M.P.H., John Hopkins senior director of infection prevention.

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If you get a negative result for COVID-19, it’s important to remember that “the test result only means that you did not have COVID-19 at the time of testing,” according to the Centers for Disease Control and Prevention.

The CDC says your body typically makes antibodies 1 to 3 weeks after infection, so it could be days before a new infection shows itself on a test.

“It’s possible you could still get sick if you have been exposed to the virus recently,” the CDC said. “This means you could still spread the virus.”

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A study in the medical journal Annals of Internal Medicine found that the probability of getting a false-negative test result on the first of four days of asymptomatic infection was 100%.

The average false-negative rate dropped to 38% once symptoms began, the study showed. Three days after symptoms started, the false-negative rate dropped to 20%.

What’s the difference in tests?

There are two types of COVID-19 tests — viral and antibody.

The viral test detects current infections, while the antibody test could show if a person had a past infection.

Viral tests, or diagnostic tests, use fluid from a nasal or throat swab or from saliva. If symptoms emerge later after a negative viral test, you may need another test to determine if you are infected.

The antibody test, done using a blood sample, determines whether antibodies have developed against the virus. According to Johns Hopkins, it takes 12 days after exposure for enough antibodies to be made to appear on a test. Additionally, it is not yet clear whether antibodies signal immunity.

The CDC says, “antibody tests should not be used to diagnose a current COVID-19 infection, except in instances in which viral testing is delayed.”

Results of coronavirus tests could take hours or up to a week, depending on the testing location.

So how risky is gathering in person?

“It’s really risky,” University of Denver professor Alex Huffman told KDVR.

Huffman, associate professor of chemistry and biochemistry and an aerosol scientist, has been studying viruses in the air. In July, he adopted a widely used model to analyze COVID-19 transmission risk. 

Huffman found that if one person is infected in a medium-sized dining room with 10 people seated for a Thanksgiving meal for two hours, there’s roughly a 60% to 80% chance that someone else will go home newly infected since people can’t wear masks when eating and drinking.

“When you talk, you have a spray of big droplets that comes out, and also a big plume of the smaller particles that come out. The smaller stuff will stay suspended in the room for a long time,” Huffman said, adding that distancing helps, but it only does so much.

The CDC says as the pandemic worsens, “small household gatherings are an important contributor to the rise in COVID-19 cases.”

However, the CDC does not completely rule out small gatherings, saying celebrating with members of your household who consistently take steps to reduce transmission poses the lowest risk of spreading the virus.

And of course, celebrating virtually is a sure-fire way to stem the spread.

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