Pooled COVID-19 Testing Feasible, Greatly Reduces Supply Use

Troy Brown, RN

August 04, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Combining specimens from several low-risk inpatients in a single test for SARS-CoV-2 infection allowed hospital staff to stretch testing supplies and provide test results quickly for many more patients than they might have otherwise, researchers found.

"We believe this strategy conserved [personal protective equipment (PPE)], led to a marked reduction in staff and patient anxiety, and improved patient care," write David Mastrianni, MD, and colleagues from Saratoga Hospital in Saratoga Springs, New York. "Our impression is that testing all admitted patients has also been reassuring to our community."

The researchers published their findings July 20 in Journal of Hospital Medicine.

"What was really important about this study was they were actually able to implement pooled testing after communication with the [US Food and Drug Administration (FDA)]," Samir S. Shah, MD, MSCE, the journal's editor-in-chief told Medscape Medical News.

"Pooled testing combines samples from multiple people within a single test. The benefit is if the test is negative, [you know that] everyone whose sample was combined…is negative. So you've effectively tested anywhere from three to five people with the resources required for only one test," Shah continued.

The challenge is that if the test is positive, everyone in that testing group must be retested individually because one or more of them has the infection, said Shah, who is also Director of Hospital Medicine at Cincinnati Children’s Hospital Medical Center, Ohio.

Mastrianni said early in the pandemic they started getting the "New York surge" at their hospital, located approximately 3 hours from New York City. They wanted to test all of the inpatients at their hospital for COVID-19 and they had a rapid in-house test that worked well, "but we just didn't have enough cartridges, and we couldn't get deliveries, and we started pooling." In fact, they ran out of testing supplies at one point during the study but were able to replenish their supply in about a day, he noted.

For the current study, all patients admitted to the hospital, including those admitted for observation, underwent testing for SARS CoV-2. Staff in the emergency department designated patients as low risk if they had no symptoms or other clinical evidence of COVID-19; those patients underwent pooled testing.

Patients with clinical evidence of COVID-19, such as respiratory symptoms or laboratory or radiographic findings consistent with infection, were considered high risk and were tested on an individual basis and thus excluded from the current analysis.

The pooled testing strategy required some patients to be held in the emergency department until there were three available for pooled testing. On several occasions when this was not practical, specimens from two patients were pooled.

Between April 17 and May 11, clinicians tested 530 patients via pooled testing using 179 cartridges (172 with swabs from three patients and seven with swabs from two patients). There were four positive pooled tests, which necessitated the use of an additional 11 cartridges. Overall, the testing used 190 cartridges, which is 340 fewer than would have been used if all patients had been tested individually. 

Among the low-risk patients, the positive rate was 0.8% (4/530). No patients from pools that were negative tested positive later during their hospitalization or developed evidence of the infection.

Team Effort, Flexibility Needed

Mastrianni said he expected their study to find that pooled testing saved testing resources, but he "was surprised by the complexity of the logistics in the hospital, and how it really required getting everybody to work together…There were a lot of details and it really took a lot of teamwork."

The nursing supervisor in the emergency department was in charge of the batch and coordinated with the laboratory, he explained. There were many moving parts to manage, including monitoring how many patients were being admitted, what their conditions were, whether they were high or low risk, and where they would house those patients as the emergency department became increasingly busy. "It's a lot for them but they've adapted really well," Mastrianni said.

Pooling tests seems to work best for three to five patients at a time; larger batches increase the chance of having a positive test and thus identifying the sick individual(s) becomes more challenging and expensive, Shah said.

"It's a fine line between having a pool large enough that you save on testing supplies and testing costs but not having the pool so large that you dramatically increase your likelihood of having a positive test," Shah said.

Hospitals will likely need to be flexible and adapt as the local positivity rate changes and supply levels vary, according to the authors.

"Pooled testing is mainly dependent on the COVID-19 positive rate in the population of interest in addition to the sensitivity of the [reverse transcriptase-polymerase chain reaction (RT-PCR)] method used for COVID-19 testing," said Baha Abdalhamid, MD, PhD, an assistant professor in the Department of Pathology and Microbiology at the University of Nebraska Medical Center in Omaha.

"Each laboratory and hospital needs to do their own validation testing because it is dependent on the positive rate of COVID-19," added Abdalhamid, who was not involved in the current study.

It's important for clinicians to "do a good history to find who's high risk and who's low risk," Mastrianni said. Clinicians also need to remember that although a patient may test negative initially, they may still have COVID-19, he warned. That test reflects a single point in time and a patient could be infected and not yet be ill, so clinicians need to be alert to a change in the patient's status.

Best for Settings With Low-risk Individuals

"Pooled COVID-19 testing is a straightforward, cost-effective, and efficient approach," Abdalhamid said. He and his colleagues found pooled testing could increase testing capability by 69% or more when the incidence rate of SARS-CoV-2 infection is 10% or lower.

He said the approach would be helpful in other settings "as long as the positive rate is equal to or less than 10%. Asymptomatic population or surveillance groups such as students, athletes, and military service members are [an] interesting population to test using pooling testing because we expect these populations to have low positive rates, which makes pooled testing ideal." 

Benefit Outweighs Risk

"[T]here is risk of missing specimens with low concentration of the virus," Abdalhamid cautioned. "These specimens might be missed due to the dilution factor of pooling (false negative specimens). We did not have a single false-negative specimen in our proof-of-concept study. In addition, there are practical approaches to deal with false-negative pooled specimens.

"The benefit definitely outweighs the risk of false-negative specimens because false-negative result[s] rarely occur if any. In addition, there is significant saving of time, reagents, and supplies in [a] pooled specimens approach as well as expansion of the test for higher number of patients," Abdalhamid continued. 

Mastrianni's hospital currently has enough testing cartridges but they are continuing to conduct pooled testing to conserve resources for the benefit of their own hospital and for the nation as a whole, he said.

The authors have disclosed no relevant financial relationships. Abdalhamid and Shah have disclosed no relevant financial relationships.

Journal of Hospital Medicine. Published online July 20, 2020. Full text

Troy Brown, RN, is an award-winning Medscape contributor with a special interest in infectious diseases, women's health, and pediatrics.

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