Getting a negative coronavirus test isn’t a free pass to gather with family for Thanksgiving

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New Yorkers wait outside a CityMD urgent care clinic on November 18, 2020.
  • Many Americans are getting coronavirus tests ahead of Thanksgiving.
  • But experts say the tests are not a free pass to gather indoors with others, since they only provide a snapshot of your infectiousness at one point in time.
  • To truly gather safely, a period of isolation is required before a test, and there should be no exposure after, either.
  • Otherwise, when seeing people outside your household, meet outdoors, wear masks, and maintain social distance.
  • Visit Business Insider's homepage for more stories.

In New York, the lines for coronavirus tests have gotten so long ahead of the Thanksgiving holiday that some people are paying line-sitters to wait for them.

Demand for the tests has surged across the country as people take precautions before traveling or gathering with family.

Although getting tested is a helpful tool in preventing spread, experts say, it's not enough on its own to ensure safe family gatherings. 

"Testing is one piece of many," Saskia Popescu, an epidemiologist at the University of Arizona, told Business Insider. "It's a reactive, secondary prevention strategy and can definitely help identify infections, but it shouldn't be used as a way to justify seeing more people."

Indeed, without isolating before and after a test, testing negative doesn't guarantee that it's safe to hang out indoors and maskless with people outside your household.

Tests provide a snapshot of your viral load

Think of a coronavirus test like a photograph: Even the most accurate molecular tests can only provide information about your viral load at a single moment in time.

A PCR test searches within a sample of sputum — the gunk found in the throat and nasal cavity — for the virus' RNA, then amplifies that RNA a bunch of times until it becomes detectable. 

But the median incubation period for COVID-19 is four to five days — that's how long it takes most people to start displaying symptoms, according to the CDC. So during the days right after infection, the virus might not have replicated and spread throughout the body enough for a PCR test to detect it. In that case, a person could test negative but become infectious — and start feeling ill — hours or days later. 

As the virus spreads throughout the body, however, eventually a person becomes both contagious and likely to test positive.

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A medical worker performs a PCR test for the coronavirus on August 31, 2020 in Montreuil, France.

Gathering safely with others indoors and without masks, then, requires a period of isolation before a coronavirus test to account for that possible incubation period. Anand Swaminathan, an assistant professor of emergency medicine at St. Joseph's Hospital in New Jersey, laid out the necessary steps: First, everyone involved must isolate for 14 days, and the quarantine should be strict.

"If your kids are going to school or playing sports or going to daycare, you're not quarantining," Swaminathan told Business Insider.

At the end of that period, all individuals planning to gather should get a coronavirus test. If nobody has illness symptoms and nobody tests positive, then it should be okay to get together, Swaminathan said.

He offered an example of what can happen when that protocol isn't followed. Swaminathan said an acquaintance of his recently attended an eight-person bachelor party. Before it, everyone tested negative. But a day after the party, one member developed symptoms and tested positive. Then three others tested positive.

"The issue was not quarantining adequately before getting together," Swaminathan said. 

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A family hosts an outdoor birthday party at their home in Brooklyn, New York, July 12, 2020.

Furthermore, he added, a negative test is only useful if you don't engage in any risky behavior after getting swabbed. In the time between getting a negative test result and seeing friends or family, people should not engage in any activity that could expose them to the virus. 

"You can be negative today, contract tomorrow, and be positive the day after," Swaminathan said.  

The White House super-spreader event

The White House's October coronavirus outbreak can be seen as another example of a worst-case scenario that illustrates the pitfalls of relying on testing alone.

At the end of September, President Donald Trump held a large, 20-minute outdoor ceremony for Amy Coney Barrett, then the Supreme Court nominee. There was also a small indoor reception. The event's 100-plus guests were required to test negative using a rapid test before attending. But once there, most didn't wear masks, and many hugged and mingled before and after the ceremony.

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Attorney General William Barr says goodbye to former New Jersey Gov. Chris Christie and other guests at the White House nomination event for Supreme Court Judge Amy Coney Barrett, September 26, 2020.

Less than a week later, President Trump tested positive for the coronavirus. At least 34 people in the president's orbit tested positive as well. 

Most likely, one or more attendees at the event were infectious when they attended, and the rapid tests the White House used didn't catch their cases. That's partly because rapid tests are less accurate than PCR tests. The White House relied on the Abbott ID Now rapid test, which can produce results in as little as 15 minutes but have been shown in some studies to produce false negatives about 9% of the time.

Other rapid tests, like antigen tests, may only pick up about 70% to 80% of infections, and can also produce false negatives. 

By contrast, PCR or molecular tests are "typically highly accurate," according to the Food and Drug Administration. UC Davis estimates that some PCR tests can be up to 100% accurate when done.

At this point, there's not enough time to isolate before a Thanksgiving gathering if you haven't started already. So it's best to follow the standard precautions that public-health experts recommend.

"If you're seeing people outside your household, keep it small, outdoors, masked when within 6 feet, and stay at your own household table for eating and drinking. And of course, hand hygiene," Popescu said. 

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