A Rapid Virus Test Falters in People Without Symptoms, Study Finds

As the number of coronavirus cases in the United States exceeds 9.2 million, experts continue to call for a massive scale-up of testing among both the healthy and the sick — a necessary measure, they have said, to curb the spread of an infection that can move swiftly and silently through the population.

One strategy has involved the widespread use of rapid tests, which forgo sophisticated equipment and can return results in minutes. Purchased in bulk by the federal government and shipped nationwide, millions of these products have already found their way into clinics, nursing homes, schools, athletic teams’ facilities and more, buoying hopes that the tests might hasten a return to normalcy.

But a new study casts doubt on whether rapid tests perform as promised under real-world conditions, especially when used in people without symptoms.

In a head-to-head comparison, researchers at the University of Arizona found that, in symptomatic people, a rapid test made by Quidel could detect more than 80 percent of coronavirus infections found by a slower, lab-based P.C.R. test. But when the rapid test was used instead to randomly screen students and staff members who did not feel sick, it detected only 32 percent of the positive cases identified by the P.C.R. test.

Quidel’s tests are authorized for use only in people with symptoms, but their use in those who are asymptomatic has been strongly encouraged by the federal government. In September, the White House announced detailed plans to purchase and distribute 150 million rapid antigen tests manufactured by another company, Abbott.

“This is really valuable data that has been hard to come by,” said Dr. Benjamin Mazer, a pathologist at Johns Hopkins University who was not involved in the study. “But 32 percent is a very low sensitivity. I’m surprised by how low that is.”

The university’s data, which have not yet been published in a peer-reviewed scientific journal, were evaluated by Dr. Mazer and several other outside experts at the request of The New York Times. Rapid coronavirus tests like Quidel’s, they said, should be rolled out with the utmost care — and come with clear-cut explanations about how the results should be interpreted. ...

ALso see:HHS relaxed oversight of problematic Covid-19 tests despite being told of accuracy concerns