Stanford to conduct COVID-19 pool testing; here's how it works and who it could help

ByKate Larsen KGO logo

Thursday, July 23, 2020

Stanford to conduct COVID-19 pool testing

Stanford got approval from the Food and Drug Administration (FDA) on Wednesday to start COVID-19 pool testing, a method that could save valuable testing supplies and prevent large outbreaks.

SAN FRANCISCO (KGO) -- Stanford got approval from the Food and Drug Administration (FDA) on Wednesday to start COVID-19 pool testing, a method that could save valuable testing supplies and prevent large outbreaks.

Pooled testing involves mixing several people's biological samples and examining them in a single test. The practice has been around for decades, but it's just now being used for COVID-19 testing in the U.S.

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Quest Diagnostics received emergency use authorization on July 18.

And as of July 22, Stanford is allowed to conduct pool testing while they wait for emergency use authorization from the FDA.

"If you're doing 100 individual tests and you're able to pool those, it becomes a thousand tests. So in a situation where there's not enough testing, it gives you the opportunity to really leverage what you have," said Jim Zehnder, the director of clinical pathology at Stanford.

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At their labs, he says pooling eight COVID tests together is optimal to prevent dilution, but he says, "it's only useful if prevalence of disease is low." The reason being, if someone in the pool tests positive, doctors would then have to test people individually to locate the infected person. So pool testing a group with a known high positivity rate would not improve testing efficiency.

"Once things are under control it's a really good way to keep an eye on things and detect outbreaks before they occur and become really big problems," explained Zehnder, who answered the following questions for ABC7.

What will Stanford use pool testing for?

"It could be for group living situations, like nursing homes."

What about testing schools or students living on campus?

"One way to think about it would be if you had a dorm with three floors, you could do the first floor one day, the second floor another day, and third floor the third day, and just repeat that every week."

Could pool testing result in false negatives?

"If there's an outbreak in a nursing home, there would be some people with a lot of virus and some people with a little bit of virus, and even if the test is a little bit less sensitive, we would detect an outbreak."

Why didn't the U.S. start specimen pooling sooner?

"People have wanted to do this for some time. It's taken some time to get through the regulatory environment to get permission to do this. It's fair to see the United States has been slow to implement these things. Arguably we should have been doing this a month ago."

But Dr. Zehnder says now that pool testing can start, he's "optimistic... that we'll get it right finally."

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