How Pooled COVID Testing Helps Keep Schools and Workplaces Safe

In the first several months of the COVID-19 pandemic, testing people for SARS-CoV-2 infection lacked efficiency, with lab bottlenecks and long turnaround time for results. But in the summer of 2020, pooled testing, where samples are batched together, emerged as a more efficient strategy for certain situations, according to the Food and Drug Administration (FDA).

Pooled testing is now being used in many schools, and experts say the approach will continue to have applications elsewhere as we seek the other side of the pandemic.

“Mid-pandemic we had a dearth of laboratory supplies and laboratory personnel and whole systems,” Mara Aspinall, MBA, co-founder and professor of practice, Biomedical Diagnostics at Arizona State University, tells Verywell. “So turnaround time was going very, very slow, and it was difficult to get a quick answer to a test. Pooling allows a highly sensitive test, but uses the testing and sampling resources effectively.”

Pooled Testing in Schools

Pooled testing allows for several samples—swabs from a whole classroom, for example—to be tested at once, Aspinall explains. If the batch produces a negative result, then everyone in that testing pool is considered negative for SARS-CoV-2 at the time. A positive result, however, means quarantining and retesting.

“In general, pooled testing allows schools to test a large population at a fraction of the cost of individual testing,” David Berlin, head of launch of COVID-19 testing for CIC Health, tells Verywell. “It provides routine surveillance of the COVID-19 status of designated groups of students, faculty, and staff that offers a means for safely returning to in-person learning.”

Aspinall says that for SARS-CoV-2, there are two types of pooled testing: pod pooling and lab pooling.

Pod Pooling

In the context of schools, a pod might consist of a small classroom and teacher. With pod testing, the students would all provide a nasal swab that goes into a large test tube. “So the power here is you’re putting them all together with a limited amount of reagent fluid—just enough to ensure that you are taking snot (taking nasal material) off each of those swabs," Aspinall says. "And if any one of them is positive, you will get a positive result.”

When a positive test occurs with pod testing, everyone in that pod will have to be retested.

Lab Pooling

With lab-based pooling, the pooling happens at the lab rather than in the classroom, Aspinall says. For example, kids will spit into individual test tubes. Then once the samples reach the lab, technicians take a small amount of saliva from each test tube and pool them into a reaction chamber. Then they add the reagents and go through the process of polymerase chain reaction (PCR) testing.

“The advantage is if that pool is positive, they don’t have to go back and get new samples," Aspinall says. “They take what is left in those individual test tubes and they test it again and they find out who is positive.”

Testing students by classroom works well for younger children, but upper grades tend to be more mobile and interact with several teachers and fellow students throughout the school day. 

Berlin says CIC offers a homeroom testing model that’s being used in 600 schools for more than 150,000 people that accomplishes sample collection for an entire facility in a matter of minutes. “Students and staff are placed into pools consisting of two to 10 members, which can be tested at any frequency that the school or district chooses,” he explains. “Schools keep track of which students are in which pool with the help of the provided software.”

If a pooled test result is positive, he adds, everyone in the pool must take precautions as if they are positive for COVID-19, and they must followup with individual testing, which CIC then provides, Berlin explains.

“It’s important to remember that no test is perfect,” Brian Cruz, MD, regional medical director of PhysicianOne Urgent Care, tells Verywell. He adds that a negative result does not provide 100% certainty that the pool is negative. “We think of it as a snapshot in time,” he explains. “There was no virus detected at that time. However, ongoing precautions still need to be taken, such as hand washing, wearing masks, and social distancing.”

Even as more adults are vaccinated, pooled testing will continue to be a valuable tool for schools. “Since COVID-19 vaccination is still not available to children under 16, ongoing testing continues to be a critical piece to help keep children in the classrooms, reduce community spread of COVID-19, and minimize the proliferation of variants," Cruz says.

Pooled Testing in the Workplace and Beyond

Pooled testing has worked well in schools, Aspinall says, because the population is stable. “You’re going to see the same people today as you’re going to see tomorrow,” she says. For that same reason, pooled testing can work well in workplace settings.

“We see some offices and other organizations beginning to adopt pooled testing and think it will be a key piece in the return-to-workplace strategy,” Berlin says. “Coworkers are pooled together at a fraction of the cost of individual testing.”

As the number of those who’ve received a COVID-19 vaccine continues to increase, pooling will remain a valuable surveillance method to mitigate outbreaks. “Even among vaccinated populations, there will likely still be some version of testing necessary moving forward,” Berlin says. “And pooled testing will be the most cost-efficient way to test groups of people. We see this as a potential strategy for different cohorts, like restaurant workers on the same shift. Even families can pool their samples together.”

As prevalence of COVID-19 decreases, the use of pooled testing may actually increase rather than phase out. “The pooled testing approach is ideal when prevalence of disease in a population is low,” Luke Daum, PhD, executive vice president and chief scientific officer of Longhorn Vaccines and Diagnostics, tells Verywell. “This is important because if too many people harbor disease, the pooled groups must be broken and individually tested.”

Daum says Longhorn Vaccines and Diagnostics has provided pooled testing to several small businesses in Texas. In one instance, he says his team received samples from 20 staffers from a company. They pooled the samples into four sets of five. One set tested positive. The samples within that set had to then be individually tested. Eventually one person was found to be positive. 

“Twenty individual tests were reduced to nine tests,” he says. “This greatly streamlined and simplified the testing process, saving valuable reagents and resources and reducing any potential for processing error. The one COVID-19-positive individual was informed and isolated from the company with results reported same day.”

Pooled testing has been a strategy used for decades, long before the COVID-19 pandemic. It’s been used to screen donated blood, watch for HIV outbreaks, or test the regional prevalence of West Nile Virus, according to an article posted by the American Society for Microbiology. Beyond the pandemic, pooled testing could have future applications for keeping people safe.

“It may have added value when larger groups require screen testing prior to travel,” Daum suggests.