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Vermont health officials investigate possible coronavirus outbreak in Manchester area

A person tested a swab sample with a rapid antigen test in Ahmedabad, India.
A person tested a swab sample with a rapid antigen test in Ahmedabad, India.SAM PANTHAKY/AFP via Getty Images

Vermont health officials are investigating a possible coronavirus outbreak in southwestern Vermont, where nearly 60 people have tested positive using antigen tests that are not traditionally counted by the state.

The state Department of Health said the cases will be considered “presumptive positive” until they are confirmed by a polymerase chain reaction (PCR) test, which are the only active coronavirus results that state authorities can include in their regular case numbers, according to Ben Truman, a spokesman for the department.

In the meantime, state authorities are responding to the suspected outbreak with their “outbreak response group” that shares information about self-quarantining and helps with the state’s contact tracing efforts. Anyone who received an antigen test — whether they tested positive or negative — should get a PCR test, Truman said.

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The state is operating a pop-up clinic in nearby Londonderry that is conducting PCR tests.

The antigen tests, which were approved by the US Food and Drug Administration in May, are “designed for rapid detection of the virus that causes COVID-19,” the FDA wrote in a statement in May, but “do not work the same way as a PCR test.”

“Antigen tests are very specific for the virus, but are not as sensitive as molecular PCR tests,” the agency wrote. “This means that positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection.”

So far, 58 people have received positive coronavirus results from antigen tests at an urgent care facility in Manchester as of Wednesday morning, Truman said. It’s not clear why the medical center is using antigen tests, but Truman said he’s not aware of any PCR test shortage in the state.

As of Wednesday, Vermont health officials have reported 1,318 coronavirus cases (not including the antigen test results in Manchester). Fifty-six people have died, and 1,104 people have recovered. More than half of the reported cases have been in Chittenden County in northwestern Vermont, which includes the city of Burlington.

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Felicia Gans can be reached at felicia.gans@globe.com. Follow her on Twitter @FeliciaGans.