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Antigen Test For COVID-19 Isn't As Reliable As Genetic Test, Experts Caution

DAVID GREENE, HOST:

All right, so there's this new kind of test for the coronavirus. It is fast, and it is also easier to use than the one most people have been getting. And with the pandemic surging in many parts of the U.S., it's in pretty big demand. But as NPR health correspondent Rob Stein reports, there are some concerns over reliability.

ROB STEIN, BYLINE: The minute Gary Burk found out he might have been exposed to the coronavirus, he knew he had to get tested right away. Burk's in charge of worker safety at a big construction site in Texas, so he understood what would happen if he was infected.

GARY BURK: I have 274 people working out here. And so if that were the case that I did come up positive, that would've meant we had to shut the project down and everybody go get tested to find out who's positive, who's negative. We were all sweating bullets.

STEIN: So Burk rushed to the nearest clinic where he could find out immediately if he had caught the virus. It came back negative.

BURK: Oh, man, I was elated. There's huge things at stake.

STEIN: Burk was able to go right back to work, and the new federal courthouse he was building could stay on track.

BURK: It was huge. You have no idea. You know, there's a lot of money involved, and it just - you know, I don't want to be the guy that spreads anything like that.

STEIN: The kind of test Burk got is a new kind of test. It's called an antigen test because it looks for a piece of the virus called an antigen in specimens collected by swabbing inside the nose. It works like those quick strep and flu tests everyone's been getting for years at their doctors' offices and neighborhood clinics. So some think it's a kind of test that the nation needs to safely reopen by quickly and easily testing millions of teachers, students, factory workers, waiters over and over again.

DOUGLAS BRYANT: If you're going to do tens of millions of tests a week, we're going to need these tests.

STEIN: Douglas Bryant is president and CEO of Quidel Corporation, which makes the test. His company can crank out millions of the tests. It only costs about $20, compared to $100 for the much more complicated genetic tests that have been used so far. And it produces results within 15 minutes, right on the spot, instead of waiting hours or even days.

BRYANT: It's the cost. It's the speed. It's actually just the capacity to do the tests.

STEIN: The Trump administration is banking on antigen tests to help finally solve the shortage of testing that has hobbled the nation's ability to stop the relentless spread of the virus. But some experts say antigen tests just aren't as reliable. They tend to miss about 20% of infections. Frederick Nolte is a testing expert at the Medical University of South Carolina.

FREDERICK NOLTE: The danger is that you will miss actively infected patients. And if you miss them, they will go on to spread the disease to others.

STEIN: And that could help let the virus spiral out of control again and again and again.

NOLTE: It has tremendous ramifications in terms of the controlling of the spread of the pandemic.

STEIN: But Quidel's Bryant says his test is much more reliable than most antigen tests, and the ability to do regular mass testing cheaply, easily and quickly would outweigh any shortcomings of these new antigen tests.

Rob Stein, NPR News.

(SOUNDBITE OF ATTUNE'S "THRILL") Transcript provided by NPR, Copyright NPR.