Pooled Testing For Coronavirus Gets Another Look : Shots - Health News Instead of running a coronavirus test on every specimen, a lab combines multiple samples. If the batch is negative, then everyone is in the clear. A positive leads to a second round of testing.

Pooling Coronavirus Tests Can Spare Scarce Supplies, But There's A Catch

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All right. With coronavirus cases spiking in some parts of the United States, there is more demand for testing. To keep up, federal health officials want to try this technique where you combine samples from a number of people and then just run one single test on them. This was a strategy that was used in China. NPR's science correspondent Richard Harris has more.

RICHARD HARRIS, BYLINE: The strategy is called pooled testing. Anthony Fauci, the nation's top infectious disease doctor, explained the concept at a Senate hearing. He says, say you have samples from 10 people.


ANTHONY FAUCI: So you put all the tests together and you do one test. If that test is negative, then you know those 10 people are all negative.

HARRIS: Of course, if it comes back positive, then you need to run 10 more tests to find the person or people who are positive. But if you're testing a population where the virus is uncommon and a lot of those pooled samples come back negative, overall, you'll end up running fewer tests and saving on testing ingredients, which are called reagents. It could also be good for bulk testing, Fauci said.


FAUCI: It can be used in any of a number of circumstances - at the community level or even in school, if you wanted to do that.

HARRIS: It's not a new concept. In fact, Peter Iwen, who heads the Nebraska Public Health Laboratory, says he started doing it for the coronavirus back in March.

PETER IWEN: The reason why it even came up in Nebraska was that we were running out of reagents back in mid-March to be able to run COVID-19 testing in the public health lab.

HARRIS: After getting permission to do so, he pooled five tests at a time and found that he could run more than twice as many tests with the same materials. He didn't get anything like five times the efficiency by pooling five samples, but it helped.

IWEN: You can save 50, 60% of reagents. But you might only be saving, let's say, 25, 30% of the labor. But you still are saving labor.

HARRIS: Of course, labs have to be set up to deal with this more elaborate workflow, which not all can do. And Nebraska actually stopped pool testing a few weeks ago because so many tests were coming back positive, they had to do a ton of testing on the original samples anyway to track down all the infections.

There's another trade-off, as well. Dr. Chris Pilcher at the University of California, San Francisco says that when you combine samples, you increase the risk of getting negative results from people who are actually infected.

CHRIS PILCHER: That specimen in the pool has been diluted by the rest of the specimens. So there's a decrease in the amount of the stuff you want to detect in the specimen. And that results in a corresponding decrease in the sensitivity of detection for the test.

HARRIS: Pilcher recently ran an analysis that found it appears to be a manageable problem.

PILCHER: You will always lose some proportion of the cases that you could find individually.

HARRIS: But he says the trade-off is worth it if pooling lets you test a whole bunch more people, say, to survey a community or a group of workers or students.

Finally, it's important to remember that the shortage of testing ingredients is only part of the challenge. Health officials struggled to get enough collection swabs and shipping vials. And people who want testing can end up in long lines at overworked collection stations, so pooling alone won't solve our testing woes.

Richard Harris, NPR News.


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