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MONTPELIER — The Northshire's antigen test mystery is getting a closer look from the federal government, according to Vermont Public Health Commissioner Dr. Mark Levine.

The U.S. Food and Drug Administration has opened an investigation into why more than 90 percent of positive antigen tests taken earlier this month at the Manchester Medical Center clinic were later contradicted as negative by PCR tests, Levine said Friday during Gov. Phil Scott's twice-weekly COVID-19 briefing.

The agency had not confirmed the presence of an investigation by press time Friday. But Levine said the FDA sat in on conversations with the state Department of Health and U.S. Centers for Disease Control and Prevention on Thursday about the discrepancy.

"FDA was in on the call and assigned a research scientist PhD to our case. ... They now have opened an investigation," Levine said.

Levine said he had no additional information about the probe. "Like any investigation you don't hear about it until they have something to tell you. They keep things very confidential," he said.

Dr. Janel Kittredge-Sterling, the co-owner of Manchester Medical Center, has said the clinic administered the tests properly and kept the equipment properly calibrated. She said the test had produced only negative results until July 1, when it returned a single positive, and then no others until July 10, when the wave of positive tests began.

Wednesday, Quidel said it was investigating the situation in person "to gather intelligence, talk with those involved, download and analyze the instrument data, and observe the physical operation."

Kittredge-Sterling said a Quidel regional lab tech from Maine and a manufacturing representative from Texas were at the clinic on Thursday.

"They were here for many hours, went through all of our procedures and protocols, participated in obtaining samples from patients, downloaded all data from our analyzers and could not find any errors with our processing," she said. "The word used was 'excellent' documentation, protocols and procedures."

The clinic has retraced its steps to assure it followed the correct protocol, Kittredge-Sterling said.

"We have gone through all patient records and have developed the detailed algorithm of contact tracing that supports the +COVID surge in this area," she said. "This has not been a coincidence nor the result of `faulty batch of assays' or Manchester Medical Center failure."

On Friday, the company said it had no additional information to report.

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Levine said the state had yet to receive data from the company, which has said it believes the positive test results are accurate. Manchseter Medical Center reported that it had 59 positive tests between July 10 and July 15, with about half of those cases coming from Londonderry and other mountain towns east of Manchester. Those figures were not reflected in the state's figures, as the state relies upon PCR tests for its public data.

Kittredge-Sterling said many of those tested were presenting mild fevers and gastrointestinal symptoms.

When the state conducted follow-up PCR tests on all 65 patients, all but four of them tested negative for the virus. In total, the state collected 1,613 samples for PCR tests in pop-up test sites in Londonderry and Manchester, and in follow-up testing of Manchester Medical Center patients, and recorded five positive tests.


Vermont is not the only place where the antigen test has been questioned. The Maine Center for Disease Control has reported that 24 summer campers in that state tested positive using the Quidel antigen test, and then tested negative with a PCR test. Levine said those patients had been asymptomatic.

An antigen test looks for proteins that are part of the virus, while the PCR test looks for its genetic structure. The antigen test is much faster, returning results in minutes, where the PCR test takes days. But the antigen test also returns a higher percentage of false negative results.

The PCR test looks for the genetic code of the COVID-19 virus, while the antigen test seeks the virus' proteins.

At issue is the Sofia SARS Antigen Fluorescent Immunoassay, the test which Manchester Medical Center has used since it was approved on an emergency basis in May. The clinic had been using San Diego-based Quidel's antigen testing equipment since it opened last year.

Quidel completed three studies on the test, all involving frozen samples, before requesting FDA authorization, The Boston Globe reported.

"It's amazing how little the FDA requires for an emergency-use application," Dr. David Hamer, an infectious disease expert at Boston University and a physician at Boston Medical Center, told The Boston Globe about the emergency approval of the test.

"We don't have any independent validation on these antigen tests," Dr. Gigi Gronvall, a biosecurity expert at the Johns Hopkins Center for Health Security, told the Globe. "Often those studies come out differently from those of the manufacturer. It's just they don't have access to the volume of samples necessary to do thorough testing," Gronvall said, according to the Globe report.

Reach Greg Sukiennik at