What is pooled testing? Here’s what experts say about using the method for coronavirus

As the U.S. continues to add thousands of new coronavirus cases a day, experts say it may be time to consider a new testing method: pooled testing.

Dr. Deborah Birx, coordinator of the White House Coronavirus Task Force, has advocated for the method, saying it could drastically increase the number of people who can be tested daily.

“Pooling would give us the capacity to go from a half a million tests a day to potentially 5 million individuals tested per day,” she said during an American Society for Microbiology conference in June, Stat reported.

But what is it? Here’s what to know about the testing method, including how it works and where it could be most effective.

What is pooled testing?

To conduct pooled testing, a lab mixes samples from several people together to make a single batch, which would then be tested for the coronavirus, according to the U.S. Food and Drug Administration.

“For example, four samples may be tested together, using only the resources needed for a single test,” the FDA said.

If one such pooled sample tests positive, then each sample in the batch will be tested individually to determine which samples are positive for the virus, according to the administration. If a batch tests negative, it’s assumed that all samples included in the batch are negative for the virus.

The idea is that the pooled batches will allow for fewer tests to be run overall, cutting down on the use of testing supplies and generally allowing for people to receive results more quickly, the FDA said.

Experts have also said since the pooled method would allow more people to be tested more quickly, then “surveillance testing” could help identify asymptomatic people who may be unknowingly spreading the virus, CNN reported.

How many samples are tested at once?

The number of samples included in a batch depends on which machine is used, Health magazine reported, and scientists have differing opinions on how many is best.

Some say a max of 10 samples can be included in a batch, while others recommend grouped samples up to 50 per batch, according to the outlet.

A recent study in Israel found that a positive sample could be detected in a batch of up to 32 samples and potentially up to 64 samples, assuming some additional protocols.

What are the downsides to pooled testing?

Pooled testing isn’t perfect.

Pooled testing samples are diluted, which means there could be less viral genetic material to detect, potentially leading to false negative results, the FDA said.

The administration also said the method works best when there is a lower incidence of the virus — more negative results expected than positive.

“If the prevalence is high, all batches are going to be positive and they will be less useful,” Dr. Amesh A. Adalja, senior scholar at the Johns Hopkins Center for Health Security, told Health.

Where should pooled testing be used?

Experts say pooled testing may not be the best option in parts of the country with high positivity rates such as Texas or Arizona, Health reported. It would be more useful in states where new cases are trending downward, according to the outlet.

The method also wouldn’t be useful in smaller settings — such as a nursing home — where multiple cases have been confirmed, according to CNN. Most batches would turn up positive, meaning it would have made more sense to test everyone individually, the outlet reported.

Pooled testing, however, could be a great option for schools, universities and large employers planning to reopen, Dr. Manisha Juthani, associate professor of medicine and epidemiology at Yale School of Medicine, told CNN.

“If one wing of a dorm, or one classroom in a school, is a pool and tested all together, that group could be cleared quickly,” Juthani told the outlet.

Birx also recommended the method for communities experiencing their first hospitalizations related to COVID-19, according to CNN.

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