How Accurate Are Virus Tests? Ohio Governor’s Results Show Positives and Negatives

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Antigen tests can provide results in less than an hour. But because the process does not amplify particles, Dr. Miller said “the ability to detect the virus is lower by definition.”

All virus tests have the possibility of an inaccurate result. “It is just a fact of clinical testing,” said Dr. Miller, who recommended using common sense about the risk of exposure when evaluating unexpected results.

But antigen tests are generally less sensitive and less accurate than the traditional nasal swab, laboratory test. Interestingly, antigen tests are more likely to produce false negatives — missing someone who has the virus — than false positives, the opposite of what appears to have happened to Mr. DeWine.

Mr. DeWine is expected to be tested again on Saturday.

States are increasingly turning to antigen tests as part of a strategy to ramp up testing. Mr. DeWine is part of a bipartisan group of governors — four Republicans and four Democrats — who are negotiating to purchase the tests from two medical companies, Becton, Dickinson & Company and the Quidel Corporation. The companies were the first to receive emergency authorization for antigen tests from the Food and Drug Administration, but the tests could produce false negative results between 15 and 20 percent of the time.

The United States is currently testing at a daily rate of 241 tests per 100,000 people, according to an estimate by Harvard Global Health Institute. By the same estimate, the country would need 355 tests per 100,000 people to slow the spread of the virus, and more than 1,000 tests per 100,000 people to truly suppress the virus by detecting and responding to outbreaks as they occur.

To ramp up enough testing, experts say the United States cannot rely on traditional one-by-one laboratory tests alone.

Antigen tests offer one strategy that could prove useful for crowded settings like nursing homes or schools. “You have the advantage of being able to quickly identify people who might be infected and getting them isolated and separated,” Dr. Miller said. “Whereas where you have to wait 48 or 72 hours for a test result to come back, you have that window of time where people are often not fully isolated or quarantined.”

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