Several large medical labs here are working out the kinks in a mass testing program that could identify positive COVID-19 cases for half to two-thirds of the current cost.

The process is called pool testing, and while it was used to detect syphilis a half a century ago, it has just recently received emergency-use authorization from the U.S. Food and Drug Administration for COVID-19 testing.

Memphis is likely ahead of many cities in the process because several of its labs applied in mid-June to the FDA for permission to use the method. Several days later, the FDA issued emergency-use approval.

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“They were learning from what our experience was,” said Dr. Manoj Jain, coronavirus medical adviser to Memphis Mayor Jim Strickland. “They were judging our experience.”

Memphis may be the only city that has applied for pool testing approval.

“I talked to people in two to three cities, Nashville, Atlanta,” Jain said. “They are not using it. It was only academic centers that are. In terms of cities, I believe we are the only one.”

Pool testing works like this: In large asymptomatic groups of people – schoolchildren going back to school, for instance, or college students in a dorm – nasal swab samples are taken from each person. The lab mixes part of the samples from five to 10 people in a batch and runs it through the test analysis. If it tests positive, the individual tests in that batch are run again to identify who was positive in the batch.

Each test is reimbursed at $100. If an employer or school tests 100 people in batches of 10, it has invested $1,000. If two of the batches are positive, for instance, the lab can run those 20 tests separately for $2,000.

In this hypothetical analysis, it would cost $3,000 to test 100 people rather than $10,000, said Jenny Bartlett-Prescott, chief operating officer at Church Health and a member of the Memphis-Shelby County COVID-19 Task Force.

“You’re not bringing everybody back in and swabbing them again because you already have the samples,” she said.

Because it costs less and requires fewer testing supplies, some experts, including Poplar Healthcare’s CEO, Jim Sweeney, say pool testing will significantly expand testing.

In a population where positivity is 1%, “it takes a limited supply chain and greatly enhances it,” Sweeney said, adding that it could provide a fourfold increase in testing, “which could be profound.”

Nebraska began using the pool approach in March without FDA approval when it was dealing with outbreaks in meat-packing plants. Under provisions of the state of emergency its governor put in place, some state and federal rules were voided and the state lab director put pooling in place for COVID-19 testing.

When the positive rate crept past 10%, Nebraska suspended the program. Pool testing is less efficient if many samples require retesting.

As cities and towns across the nation face the opening of school late this summer, experts say the method makes sense because it could identify the handful of infected among a vast majority that is not.

Baptist Memorial Healthcare, which is consulting with Rhodes College on its reopening plans, sees pooling as a way to strategically ramp up testing, based on different exposure factors, including size of the group, length of the class period and ventilation specifics in a space.

“So far, pools between five and 10 appear to be quite accurate,” said Dr. Stephen Threlkeld, co-director of Baptist’s infectious disease program.

“One could adapt pool testing to that stratified risk. And it’s important to have strategy,” he said, noting it would make sense to test higher-risk groups more often.

“It would allow you to do wider-spread testing, particularly in situations like dormitories, where it would be important to know if there were a small outbreak to prevent it from becoming larger.”

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Memphis, Jain said, is ahead because as early as mid-spring it was envisioning ways to build mass testing capacity and rolled out a pilot of city employees in early June.

“How does one reach them? If we offer it, will they take up the offer?” said Jain, who was pleasantly surprised with the results.

Fifteen hundred firefighters, police and other employees volunteered to be tested.

“If we can figure out the structure of how to do the testing, then we can see how it fits in to make businesses, schools and workplaces safer,” Jain said.

Pooling seems effective as long it is used to test a population where the prevalence of disease is low.

As testing ramps up here for people without symptoms, dozens are audiences seem likely, Sweeney said.

“So, if we know for example, that we’re getting samples from a nursing home that hasn’t had an outbreak, or we’re testing the firemen or we’re testing this company, and they haven’t had any breakouts but they want to be proactive, you can pool all those people.”

Pooling will identify the one or two in a generally asymptomatic group that might be carriers.

The test method does require a second test, which can delay results.

“It just basically doubles the turnaround time. To add that extra step, you’re running two arrays of tests, rather than one. … You still have to do the first screening, and then take those positive pools and separate them into individual specimens,” Threlkeld said.

If there is a criticism, it is that the method requires a second layer of testing, which Threlkeld says “could lead to people spreading the virus while you’re waiting for the extra step to be done.”

Jain, who was part of World Health Organization delegation to India last fall to work on its tuberculous outbreak, was briefed on how India was using pool testing in tuberculosis.

“It was side knowledge. I never thought I would be using that to think about processes we would be applying here,” he said.

“Then I did some research and saw that Europe had used it, and Asia had used it, and Nebraska, of all places, had one lab and was also piloting it.”

When Jain suggested the approach to Strickland, it became central to the city’s effort to help the region build testing capacity large enough that tens of thousands could be tested a day.

Decisions about how often employees and students will need to be tested “are being made as we speak,” Threlkeld said late last week.

“We’re utilizing statisticians nationally as well as internationally, because I think one size does not fit all.”

It’s likely testing will reflect one’s particular risk.

People on sports teams and in choirs may be asked to test more frequently, he said.

“We just have to take advantage of that knowledge and test people with an eye toward what the risk is.”