Health experts including Dr. Anthony Fauci have mentioned in recent interviews that U.S. leadership is considering a strategy called “pool testing” or “batch testing” as an efficient way to test large swaths of people for Covid-19.
Dr. Deborah Birx, the coordinator for the White House’s coronavirus task force, said recently that “pooling would give us the capacity to go from a half a million tests a day to potentially 5 million individuals tested per day.”
How does it work?
On a basic level, pool testing is a way to do disease surveillance without the need to run tests for every individual person (though you still need their samples). It’s when samples from multiple people — like say, coronavirus nasal swabs — are tested together in a single tube. Even though the samples are mixed together, the test provides a single result for that grouping of samples.
One of the best explanations of how it works logistically is from Scientific American:
Group testing is a numbers game. Let’s say you are examining 100 people, and one of them is positive. Normally you would do 100 diagnostic tests, searching for genetic material from the virus in each individual. But with group testing, you can divide those 100 people into five groups of 20. That gives you five pools with 20 samples, and you use one test per pool. If the first four sample pools test negative, you have eliminated 80 people with four tests. If the last pool tests positive, you retest each sample in that last pool individually to identify the one with the disease. In the end, you did 25 tests instead of 100.
While the samples are mixed for the test, ideally there’s still enough initial samples from each person to run individual tests if needed rather than asking people for samples a second time.
The concept of pool testing is credited to Robert Dorfman and David Rosenblatt, economists who, during World War II, developed the idea as a way to detect draftees with syphilis. Blood samples of men were tested together, and if all the tests came back negative, the men were deemed healthy. If a group test was positive then every person in the group was tested. Pool testing has since been used for other diseases like HIV and malaria when testing kids were hard to come by or expensive.
Other countries are already using pool testing for Covid-19. The Washington Post reports that India combines 25 samples to test together from migrant workers and international travels in quarantine in areas of the country where the prevalence of Covid-19 is low. Germany and Singapore also use pool testing in nursing homes.
One of the reasons the U.S. is not already using pool testing is that the FDA considers it a modification out of compliance with usual testing standards. Individual labs are getting approval for the practice, the Post reports.
It’s unclear exactly how the U.S. would plan to implement a strategy like this. As Amesh A. Adalja, MD, a senior scholar at Johns Hopkins Center for Health Security, shared with the Medium Coronavirus Blogthat it makes sense to implement a strategy like this in an area with a high number of people but a low prevalence of disease like, say, Vermont. In an area with high prevalence, like Florida, so many groupings would be positive that health experts would likely end up needing to run all the tests anyway. Adalja says it could make sense in an area with little spread or in a hospital setting, where people could be tested in batches by floor, for example.
In the Washington Post, experts suggested a strategy like this could be considered in places like camps, schools, prisons, and workplaces in low-transmission areas. The Post also added that the same pools could be tested multiple times to ease concerns over false negatives.
“It could be very useful in back-to-work or back-to-school programs or large-scale screening because this allows you to test more people and test them more frequently, and that’s the key,” Benjamin Pinsky, director of the Clinical Virology Laboratory at Stanford University’s School of Medicine, told the paper.