More than a year after the COVID-19 pandemic started spreading across the globe, laboratories are preparing for what is next. Vaccination rates are increasing, and infection rates are beginning to decline. Yet testing will remain necessary for virus surveillance as the world gets “back to normal.”
As the prevalence of COVID-19 infections drops, pooling—or testing of pooled samples—holds promise as an efficient, cost-effective approach for more frequent surveillance testing of the SARS-CoV-2 virus. In a recent webinar, Weston C. Hymes, M.S., MB (ASCP), ARUP Laboratories R&D Scientist IV, and Manohar Furtado, Ph.D., Director R&D, Genetic Testing Solutions at Thermo Fisher Scientific, spoke about testing “after the surge” and how pooling can be used to exponentially increase testing efficiency, enabling a higher volume of sample processing in populations with low infection rates.
During the webinar, Furtado explained how pooling can provide a useful workflow for large-scale testing. “Pooling may be a format we can expand to serve widespread population testing, especially in low prevalence areas,” said Furtado. “A lot of that is going to be put to use soon when you want schools to open and people coming back to work.” Furtado went on to explain that pooling not only increases testing capacity – enabling labs to accelerate time to results and reduce testing backlogs – it is also saves on use of reagents and plastics, as multiple samples may be analyzed simultaneously in a single reaction.
The workflow for pooling involves taking a small amount of viral transport media (VTM) from up to five individual collection vials and combining the samples together to create a pooled sample. When test results from a sample pool come back negative, all individual samples in the pool are considered negative. If the pool comes up positive or inconclusive, the lab will return to the original samples and retest them individually to determine which samples are positive. Since only a small amount of VTM was used for the initial pool, the lab should have enough remaining to run the single tests.
How can lab directors determine if pooling is appropriate for their labs? The Centers for Disease Control and Prevention (CDC) recommends using the positivity rate average over seven to 10 days to determine pooling efficiency.[1] “There’s an indirect correlation between the positivity rate in the population and the pooling efficiency,” said Furtado. “In general, 5% or less is considered a good point in time to pool about five samples. If the positivity rate is greater than 25%, then it’s recommended that pooling is not going to be useful.”
In the webinar, Furtado also discusses alternate methods of pooling, including swab pooling.
[1] https://www.cdc.gov/coronavirus/2019-ncov/lab/pooling-procedures.html