Researchers have devised an online test that simulates pooled testing strategies for SARS-CoV-2 that can help public health officials make the most of SARS-CoV-2 test supplies and increase the number of patients tested, as well as the number of cases detected.
While pooled testing — a method which involves mixing test samples from several individuals into a single “pool” and testing that combined sample to conserve testing resources — is useful for population screening and in settings that are resource-constrained, there are several drawbacks, including a more complicated workflow, a lower sensitivity for low-VCN patients, and the need for repeat testing for positive pools, researchers found.
Nevertheless, the easy-to-use COVID19 Pool Tool may help policy makers make decisions on a regional and national level about the advantages and disadvantages of pooled testing for SARS-CoV-2. A research letter assessing the tool was published in JAMA Network Open.
“Policy makers are promoting pooled testing as a strategy to increase the number of people tested for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the coronavirus disease 2019 (Covid-19) pandemic, especially for population screening. However, combining samples before testing brings trade-offs, such as decreasing the sensitivity and increasing the complexity of testing, that should be considered,” explained Christopher R. Polage, MD, MAS, of the Duke Health System Clinical Laboratories, Durham, North Carolina, and colleagues.
They created the COVID19 Pool Tool, an online diagnostic tool that uses actual SARS-CoV-2 virus copy number (VCN) data to help policy makers understand how pooled testing compares with single-sample testing for SARS-CoV-2 in different populations.
Using droplet digital polymerase chain reaction (PCR), they counted SARS-CoV-2 copy numbers in patient samples. After creating quantitative curves for three FDA Emergency Use Authorized SAR-CoV-2 reverse transcriptase-PCT qualitative tests, Polage and colleagues converted positive nasopharyngeal PCR cycle threshold values to droplet digital PCR-harmonized VCNs.
Users of this online tool can define sample and pool sizes, positivity rates, and test characteristics. With the comparisons between pooled testing with single-sample tests made possible with the COVID19 Pool Tool, which uses VCNs from preprocedural screening samples and outpatient diagnostic samples, the researchers were able to simulate both asymptomatic and symptomatic SARS-CoV-2-positive patients.
Pooled testing increased the number of false-negative cases per 1,000 patients and decreased the sensitivity of SARS-CoV-2 detection, particularly in low-VCN samples and asymptomatic patients, Polage and colleagues reported. And, while this form of testing also decreased the number of tests needed to screen 1,000 patients, the effect was reduced by the repeat testing needed to identify positive pool cases for contact tracing. In addition, pooled testing identified more positive patients per 1,000 tests performed due to increased patient testing, but again, repeat testing reduced this benefit.
The need to increase and improve mass testing throughout the continuing pandemic is of paramount importance, according to Christopher D. Pilcher, MD, of the University of California, San Francisco, who authored an editorial to accompany the research letter from Polage et al.
“We now recognize that a greatly expanded capacity for mass screening will be essential to managing life and economic activity in an ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. We also know that identifying asymptomatic people with acute SARS-CoV-2 infection requires frequent testing and results that are available quickly enough to act. Rapid antigen tests that can do this have been developed and their production is increasing, but the scale of capacity needed for effective screening is truly daunting,” Pilcher wrote.
He cautioned that pooling algorithms may be difficult to implement due to a lack of experience with the necessary high-speed robotic testing on the part of laboratories.
“Although these challenges are very real, they are exactly what state, regional, and national public health programs know how to do best. Countries that are facing new waves of SARS-CoV-2 infection need ways to multiply their existing capacity and to do so quickly. With reliable data to guide implementation of highly efficient algorithms, the laboratories that already have pooled testing capability need only the right directives, funding, support, and regulation. A new mass screening solution is at hand and it is past time to act,” Pilcher concluded.
One limitation of this study is the lack of clinical data for laboratory samples.
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A new tool that simulates pooled testing strategies for SARS-CoV-2 may lead to increased patient testing and increased number of cases detected, all while sparing SARS-CoV-2 test supplies.
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The COVID19 Pool Tool generates random virtual pools with positive samples pulled from VCN data that mirrors expected positivity rates and calculates pool VCNs with the expected dilution, helping policy makers identify where a pooled testing strategy would be most effective.
E.C. Meszaros, Contributing Writer, BreakingMED™
Polage and Pilcher reported no financial disclosures.
Cat ID: 190
Topic ID: 79,190,190,926,192,927,151,928,925,934
