Pooled Testing for Covid-19 Possible in US

Yesterday The New York Times outlined a hopeful new Covid-19 testing approach under consideration in the US: pooled samples.

This technique has been used for a long time in scientific fields, and basically involves combining (“pooling”) samples from multiple people while retaining a portion of each individual sample. The result from the pooled sample determines whether the individuals need to be tested.

“Here’s how the technique works: A university, for example, takes samples from every one of its thousands of students by nasal swab, or perhaps saliva. Setting aside part of each individual’s sample, the lab combines the rest into a batch holding five to 10 samples each.

“The pooled sample is tested for coronavirus infection [and] the overwhelming majority of pools are likely to test negative. But if a pool yields a positive result, the lab would retest the reserved parts of each individual sample that went into the pool, pinpointing the infected student.”

Pooled testing graphic from USA Today

China used pooled testing to check all 11 million residents of Wuhan. Germany, Israel and Thailand have also been using the technique for Covid-19 testing. Estimates show pooled testing could conserve supplies and increase testing capacity by at least 70 percent.

“We’re in intensive discussions about how we’re going to do it,” Dr. Anthony S. Fauci, the country’s leading infectious disease expert, said in an interview. “We hope to get this off the ground as soon as possible.” Adm. Brett Giroir, deputy secretary of health and human services, said he expected the program to be up and running by the end of the summer.

Asked why the administration’s stance has changed now, Dr. Fauci referred to the alarming rise in infections nationwide. “Obviously, things are not going in the right direction,” he said.

IEEE Spectrum has a more in-depth discussion for those interested. Limitations occur when the number of infected people rises above 10 per 100, because so many pools are likely to yield positive results that the labs have to go back and test more individual samples. Pooled testing also doesn’t work well for time-consuming tests, because if a pool comes back positive the patients have to wait again for the individual tests to be completed.

Also, test kit manufacturers typically have to demonstrate to FDA that pooled testing works for the method. For example, combining saliva samples could result in more dilute viral material, producing a false negative. FDA is sharing requirements with manufacturers to facilitate test method validation.

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