Workers running coronavirus tests at the Vermont Health Department lab
Many of the test results that suggested a large coronavirus outbreak in southern Vermont appear to have been flawed, state health officials said on Friday.
The Vermont Department of Health has only been able to confirm two infections in the Manchester-Londonderry area so far this week, and all 405 samples processed from a pair of emergency testing sites have come back negative for the virus.
“This is a good indication that these cases are not spreading within the community,” Health Commissioner Mark Levine said.
Town residents began panicking last weekend as local doctors at an urgent care clinic reported a sudden spike in positive COVID-19 tests. Manchester Medical Center, an independent commercial clinic, has reported roughly 60 positive tests over the past week — far more than the total cases recorded in nearby towns since the pandemic began. Businesses shut down, the weekend farmers market was canceled, and rumors abounded about the sources and severity of the suspected outbreak.
But the clinic was using a new antigen test for the virus that causes COVID-19, which state health officials don't recognize in their official data. So while the state scrambled to trace patients' recent contacts and set up mass testing sites, it also sought to verify the initial cases by using the traditional polymerase chain reaction, or PCR, testing method.
As of Thursday night, only two of 17 completed retests could be confirmed as positive COVID-19 cases, Levine said at a Friday press conference. The other 15 were negative.
"Although our investigation is not complete, it appears that many of the positive antigen results reported by Manchester Medical Center might have been false positives," Levine said.
State officials said they still don't have enough information to confirm the presence of an outbreak. The state was still waiting for hundreds of outstanding tests, plus dozens of confirmatory PCR tests for those who had tested positive through the antigen method.
The antigen test used at Manchester Medical Center was approved in May by the U.S. Food & Drug Administration, though it is not used widely in Vermont and health officials here consider it relatively unproven. Antigen tests can provide results in just 15 minutes, whereas the traditional PCR tests take days to be processed. The antigen tests, however, are known to miss as many as 20 percent of infections — what's known as a "false negative" result.
A positive antigen result is typically seen as very reliable, making the spate of likely false positives in Manchester especially befuddling. Levine suggested that the problems could stem from a "systematic issue" in how the test kits were being processed at the clinic, but he said the department needed more data.
Levine also noted that many of the antigen tests were performed on patients who did not have COVID-19 symptoms. The tests were only studied on people with symptoms, and current federal and other public health guidance does not recommend their use in general screenings.
Dr. Janel Kittredge-Sterling, one of the clinic's co-owners, has emphatically defended the positive antigen test results on Facebook and in a Thursday interview with Seven Days. On Friday, as Levine called more of those results into question, she continued to express confidence but wrote in a text message that "we have to be critical of all data."
The state recorded nine new coronavirus cases statewide on Friday, bringing the total since March to 1,334. Of those, just over 200 are considered active infections. Four patients are currently hospitalized.