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Scientists warn restaurants against reading too much into workers' negative COVID-19 tests

Basic Kitchen salad

Basic Kitchen on Wentworth Street. File/Grace Beahm Alford/Staff

Negative results from COVID-19 tests, which many Charleston-area restaurant owners have made a linchpin of their strategies for reopening after a confirmed employee case, are not reliable indicators of whether a person is capable of spreading the deadly disease, scientists say.

“We have no idea what the false negative probability is for someone without symptoms,” says A. Marm Kilpatrick, a disease ecologist at the University of California Santa Cruz.

False negatives are considered a threat to community health because studies suggest people who don't know they're sick could be responsible for transmitting nearly half of coronavirus cases.

Kilpatrick recently laid out the problem in a Twitter thread developed in collaboration with University of Washington biologist Carl Bergstrom. While studies show upper respiratory tract swabs appear to produce accurate results more than nine times out of 10 when the person being tested has coronavirus symptoms, there is no data on false negatives in the asymptomatic population.

Or, as Kilpatrick put it in her tweet, “We have NO IDEA … no information at all.”

Even though vast numbers of asymptomatic people have been tested, researchers haven’t tracked at precisely what point between infection and symptom onset their tests begin turning up positive. The Atlantic this week reported a model suggesting 38 percent of infected people will still test negative five days after exposure.

Additionally, some infected people never develop symptoms, so may not have reason to doubt their results.

In other words, Kilpatrick says, the only fail-safe course for a restaurant to take is to require all employees who had close contact with the infected person to self-quarantine for two weeks following exposure, per Centers for Disease Control and Prevention guidelines.

“Can’t you just test all your asymptomatic employees and if negative go back to work?” Kilpatrick says in response to an imaginary owner’s protestations. “Nope.”

But with few restaurants set up to schedule staff in distinct cohorts, a 14-day isolation period for employees amounts to a total stoppage, an unappealing prospect on the heels of a revenue-obliterating lockdown. Negative tests have understandably emerged as a popular alternative to waiting out the two weeks, particularly since restaurants are operating without state or local rules to govern their opening decisions.

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“We don’t have the entire staff’s test results back, but so far the person exposed and another co-worker are both negative and no one is showing symptoms,” the owners of Xiao Bao Biscuit on Tuesday announced via Instagram, one day after shutting their doors momentarily in connection with employee exposure.

“I know hitting pause every time there’s a maybe is not a way to survive in today’s world,” they continued. “(It’s) very much a Wild West-type atmosphere that we are living in.”

By which they meant there remains no standardized response to an employee testing positive, even though COVID-19 is galloping through the hospitality sector.

Many area restaurants are so keen to stay in business that they’ve skipped the voluntary step of closing when an employee tests positive. Kiawah Island Golf Resort, for instance, on June 15 released a statement reiterating that Jasmine Porch would continue to operate despite a confirmed case.

The upscale vacation destination on Tuesday revised its position, announcing it would temporarily close in the face of multiple employee cases. SNOB earlier this month made the same turnabout when employee cases mounted.

Still, more than 40 restaurants in the greater Charleston area have chosen to disclose employee cases and suspend service temporarily.

Yet, once a restaurant has gone offline, its owner has to decide when to reopen. At Basic Kitchen, corporate policy calls for closing as soon as a positive test is reported, and then calculating the reopening based on when the infected employee was last in the restaurant.

Owner Ben Towill says he counts “14 days since their last date of work, with no symptoms shown among staff,” but will wave the all-clear flag sooner if employees pass their COVID-19 tests.

Basic Kitchen closed last Wednesday, and upon “receipt of all negative test results,” opened back up on Friday.

Reach Hanna Raskin at 843-937-5560 and follow her on Twitter @hannaraskin.

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