OBJECTIVES: Pool testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) preserves testing resources at the risk of missing specimens through specimen dilution .
METHODS: To determine whether SARS-CoV-2 specimens would be missed after 10:1 pooling, we identified 10 specimens with midrange (ie , 25-34 cycles) and 10 with late (ie ,> 34-45 cycles) crossing threshold (Ct) values and tested these both neat and after 10:1 pooling . Final test results and Ct changes were compared .
RESULTS: Overall , 17 of 20 specimens that contained SARS-CoV-2 were detected after 10:1 pooling with the Xpert Xpress SARS-CoV-2 Assay (Cepheid), rendering an 85% positive percentage of agreement . All 10 of 10 specimens with an undiluted Ct in the mid-Ct range were detected after 10:1 pooling, in contrast to 7 of 10 with an undiluted Ct in the late-Ct range . The overall Ct difference between the neat testing and the 10:1 pool was 2.9 cycles for the N2 gene target and 3 cycles for the E gene target . The N2 gene reaction was more sensitive than the E gene reaction, detecting 16 of 20 positive specimens after 10:1 pooling compared with 9 of 20 specimens .
CONCLUSIONS: An 85% positive percentage of agreement was achieved, with only specimens with low viral loads being missed following 10:1 pooling . The average impact on both reverse transcription polymerase chain reactions within this assay was about 3 cycles.