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What is pooled testing? How lessons from the HIV epidemic could help fight the coronavirus

The White House Coronavirus Task Force is considering sample pooling as a way to ramp up local authorities’ ability to determine the extent of the infection.
Image: Lab testing
A researcher works in a lab that is developing testing for the COVID-19 coronavirus at Hackensack Meridian Health Center for Discovery and Innovation on Feb. 28, 2020 in Nutley, N.J.Kena Betancur / Getty Images file

A testing strategy that helped fight HIV could offer the United States a window into the severity of the coronavirus outbreak.

The White House Coronavirus Task Force is considering sample pooling, also known as pooled testing, as a way to ramp up local authorities’ ability to determine the extent of the infection in their areas, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNBC on Friday.

“It’s not going well. I have to tell you, it’s not going well,” he said in an interview with CNBC’s Meg Tirrell. “What we need to do is we need to rethink, and we are right now, the idea of many more tests getting into the community and even pooling tests.”

Pool testing involves taking samples from multiple people and testing them together in a single batch.

It doesn’t distinguish whether individual samples are positive or negative. If the results come back negative, all of the samples are reasonably assumed to be negative. If the results come back positive, the lab needs to go back to each individual sample and retest it to find out which is positive and which is negative.

Dr. Thomas Quinn, director of the Johns Hopkins Center for Global Health, used pool sampling during the HIV crisis when testing kits were rare and expensive.

"You’ve cut the cost significantly and yet you’ve gotten the actual individuals who were positive for that infection," he said.

China used pooled sampling to screen 10 million citizens in Wuhan in a matter of days, according to The New York Times.

Consideration of this testing strategy comes as many U.S. states are experiencing a significant increase in coronavirus cases, positivity rates and hospitalizations. And while states are testing more people, skepticism remains about whether the country has a handle on just how bad the outbreak has become. Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, said Thursday that the coronavirus infections may be 10 times higher than reported.

Dr. Chris Pilcher, a professor of medicine at the University of California at San Francisco, said he was originally skeptical that pool testing would work for the coronavirus, citing concerns about the sensitivity of tests and the need to dilute samples when testing.

But research from Europe and China showed the coronavirus' viral load — a measure of just how many pieces of the virus are present in a person's sample — tends to reach high levels quickly in typical infections. Pilcher said that this data, along with his previous research using pool testing for HIV, led to work that showed the method could work on coronavirus testing.

Pilcher has written a paper on the subject and said it has been seen by members of the White House Coronavirus Task Force. It's also pending publication in an academic journal.

Pool testing could offer a way to quickly ramp up testing of groups that might otherwise not be able to access tests.

"We could actually start doing surveillance, real surveillance where you test a representative sample of your population," he said.

There is already some momentum for pool testing. Quinn said he had heard that cash-strapped public health departments had already begun considering pool sampling. In mid-June, the Food and Drug Administration issued expectations for sample pooling, providing the guidelines that must be met for an emergency approval of the strategy.

"These public health departments have been underfunded for many years, so they’re always looking for alternatives," Quinn said.

Sample pooling is not perfect, and false negatives are still a concern. But Pilcher said that the ability to quickly test large groups of people with reasonable accuracy could mean a significant shift in how public health departments approach re-openings of the local economy.

But there are some concerns that sample pooling could offer a bit too much assurance. Eugene Litvak, an adjunct professor of operations management at Harvard University's Department of Health Policy and Management, said that the very basic pooling invented by Harvard University Economist Robert Dorfman in 1943 as a way to test soldiers for syphilis can increase the false negative rate.

Litvak, who worked with Quinn on sample pooling around HIV in the 1990s, said it is important to do split-pooling, in which multiple tests are taken and positive tests split into other groups. This offers the advantage of retaining the advantages of pool testing while boosting its accuracy.

It's something, he said, the U.S. can roll out.

"It’s absolutely feasible to do in the U.S.," he said. "Moreover, I think it is much needed, and I don’t see any alternative to the pooling."