But in Vermont, positive antigen tests, a relatively new way to detect an active COVID infection, require confirmation by another test: a polymerase chain reaction, or PCR, test, the gold standard used by the government, hospitals and professional sports teams. . Of the 65 people who had received such positive antigen tests, 48 would ultimately be PCR negative. Liebig was one of them.
A community on the edge was now a confused community. Had there been an outbreak? The state health department said no, while the clinic maintained its findings that showed positive results. The Manchester City Facebook forum erupted with questions about the antigen tests, cleared in May by the FDA for emergency use. What to do with this apparent test stalemate?
Attempts to answer that question proved to be a lesson in the current fractured state of evidence in the United States, as well as a reminder of how little is still known six months after the coronavirus pandemic and the methods used to mitigate its spread.
Antigen tests, which also require a nasal swab but can yield results in as little as 15 minutes, have been heralded as a cheap and quick alternative to cumbersome and expensive PCR tests, which in the United States can take anywhere from one day to two weeks. process. Instead of taking the vials to a laboratory where they are heated, cooled, and spun, the antigen test cassettes are inserted into a small on-site machine that quickly reads the results.
But although the antigen test was recently authorized by the Food and Drug Administration, it is not formally approved, meaning that only a handful of studies, submitted by the same companies that market the product, have been completed to verify its reliability.
“It is surprising how little the FDA requires for an emergency use application,” said Dr. David Hamer, an infectious disease expert at Boston University and a physician at the Boston Medical Center. “For me, the antigen test just isn’t ready for primetime use, especially to identify individual infections.”
Given the danger posed by the virus, the government has tried to act quickly to provisionally approve new medical products that could help improve the shortage and mitigate the spread of the virus. Other devices that have been authorized, but not officially approved, include face masks and fans, as well as PCR tests from companies like Abbott.
Unlike PCR tests, which detect the presence of genetic material, antigen tests detect specific proteins on the surface of a virus. In May, the rapid antigen test for COVID-19, conducted by San Diego-based Quidel, became the first of its kind available for public use. A second product, made by New Jersey company Becton Dickinson, also received authorization in July. The Manchester clinic uses the Quidel test.
Quidel completed only three studies on his product, all with frozen samples, before requesting authorization. A package insert for the product warns that “the performance may be different with fresh samples.” Such sparse data is typically insufficient for public use, but the federal government’s Emergency Use Authorization authority allows unapproved medical products to be used in public health emergencies when there is no approved alternative available.
“We don’t have any independent validation on these antigen tests,” said Dr. Gigi Gronvall, a biosecurity expert at the Johns Hopkins Center for Health Safety. “Often those studies are different from the manufacturer’s. It’s just that they don’t have access to the volume of samples needed to do extensive testing. “
But even limited studies have shown that sensitivity is the Achilles’ heel of the test, which means that sometimes the test produces false negatives. In one study, 20 percent of COVID positive cases were lost. False negatives usually come from those with smaller viral loads, who are not too contagious at the time of testing.
Still, this remarkable lack of sensitivity doesn’t explain what went wrong in Vermont. The clinic may have received a faulty batch of tests or the processing machine may not function properly. Quidel has sent a representative to Manchester to oversee and investigate operations, according to Bill Sklar, a company spokesman. Manchester Medical Center maintains that it followed the protocol while conducting the tests, while the Vermont health department is treating the results as a group of false positives.
“At this time, there is nothing to indicate a failure of Quidel’s test system,” said Sklar. “We do not want to get ahead of the events in Manchester, but we will work tirelessly with the authorities there to determine the truth and respond accordingly.”
But not all states classify results that way. In fact, the way each state looks at positive antigen tests speaks to the disjointed nature of the nation’s pandemic response, despite its porous state borders and roaming population. Rhode Island and Massachusetts include positive antigen tests in their daily total of cases, while Vermont and New Hampshire require confirmation by PCR. New York, where Liebig lives, is treating him as an allegedly positive case for COVID and mandatory quarantine, despite his negative PCR test.
Liebig is relatively certain that it is negative since she herself has shown no symptoms and no one around her has reported symptoms. But she is concerned that this test debacle and the dispute between the clinic and the state only exacerbate skepticism of the test systems.
“I took the test because I wanted to err on the side of caution, but this incident definitely makes me question the numbers to some degree,” he said. “It fuels all the conspiracy theories that this is a kind of political machine to prevent Trump from being elected. It’s all very frustrating. “
Still, some experts argue that the clinic should probably not administer the test in the first place. Dr. Janel Kittredge, owner of the Manchester clinic, told the Manchester Journal that she chose to purchase the antigen test after having difficulty obtaining the PCR test kits. Other private practices across the country are doing the same, in part because of a shortage and in part because of the low price of the antigen test, from which they can quickly make a profit.
The Manchester Medical Center charges $ 65 for a swab for an antigen test, while PCR tests are generally offered free of charge. In Massachusetts, CareWell Urgent Care clinics offer PCR and antigen tests for $ 160 each, but warn that the former may take 10-14 days to process.
But the rapid antigen test is most effective when performed on a large group of individuals almost daily. Each person would have an up-to-date idea of their infection status and, even if the test omits some cases, it would probably identify the most contagious of the group. PCR tests, by comparison, are quite accurate, but can take days to return the results, rendering them obsolete since a person could have become infected in the interim period.
Until there is a vaccine, testing is widely seen as the best tool to contain future infections and allow a return to normal. Some infectious disease doctors see antigen testing as the key to opening the door to a reality in which students can be tested before each school day or fans before each sporting event. The Trump administration announced a small step in that direction last week through a plan to provide nursing homes in affected areas with a limited supply of antigen tests to screen residents and nurses weekly. Massachusetts officials are not aware of any Massachusetts nursing home receiving such assistance, according to the state department of health.
“If only the federal government fine-tuned them and then produced them into hundreds of millions or billions, it could practically stop transmission overnight,” said Dr. Michael Mina, an assistant professor of epidemiology at the School of Har Chan Public Health TH Chan. . “There is a whole new world to have.”
Hanna can be contacted at [email protected]. Follow her on twitter @hannaskrueger.
