Pooling of SARS-CoV-2 samples to increase molecular testing throughput

Perchetti, Garrett A.; Sullivan, Ka-Wing; Pepper, Greg; Huang, Meei-Li; Breit, Nathan; Matthias, Patrick; Jerome, Keith R.; Greninger, Alexander L.

BACKGROUND: SARS-CoV-2 testing demand has outpaced its supply. Pooling samples for lower risk populations has the potential to accommodate increased demand for SARS-CoV-2 molecular testing. OBJECTIVE: To evaluate the sensitivity, specificity, and reproducibility of 4-way pooling of SARS-CoV-2 specimens for high-throughput RT-PCR. STUDY DESIGN: Individual samples were pooled 1:4 through automated liquid handling, extracted, and assayed by our emergency use authorized CDC-based RT-PCR laboratory developed test. Positive samples were serially diluted and theoretical and empirical PCR cycle thresholds were evaluated. Thirty-two distinct positive samples were pooled into negative specimens and individual CTs were compared to pooled CTs. Low positive samples were repeated for reproducibility and 32 four-way pools of negative specimens were assayed to determine specificity. RESULTS: Four-way pooling was associated with a loss of sensitivity of 1.7 and 2.0 CTs for our N1 and N2 targets, respectively. Pooling correctly identified SARS-CoV-2 in 94 % (n = 30/32) of samples tested. The two low positive specimens (neat CT > 35) not detected by pooling were individually repeated and detected 75 % (n=6/8) and 37.5 % (n = 3/8) of the time, respectively. All specimens individually determined negative were also negative by pooling. CONCLUSION: We report that 1:4 pooling of samples is specific and associated with an expected 2 CT loss in analytical sensitivity. Instead of running each sample individually, pooling of four samples will allow for a greater throughput and conserve scarce reagents.