Swab pooling for large-scale RT-qPCR screening of SARS-CoV-2 (preprint)

ABSTRACT

Pool testing has been proposed as an alternative for large-scale SARS-CoV-2 screening. However, dilution factors proportional to the number of pooled samples have been a source of major concern regarding its diagnostic performance. Further, sample pooling can lead to increased laboratory workload and operational complexity. Therefore, pooling strategies that minimize sample dilution, loss of sensitivity, and laboratory overload are needed to allow reliable and large-scale screenings of SARS-CoV-2. Here, we describe a pooling procedure in which nasopharyngeal swabs are pooled together at the time of sample collection (swab pooling), decreasing laboratory manipulation and minimizing dilution of the viral RNA present in the samples. Paired analysis of pooled and individual samples from 613 patients revealed 94 positive individual tests. Having individual testing as a reference, no false-positives or false-negatives were observed for swab pooling. A Bayesian model estimated a sensitivity of 99% (Cr.I. 96.9% to 100%) and a specificity of 99.8% (Cr.I. 99.4% to 100%) for the swab pooling procedure. Data from additional 18,922 patients screened with swab pooling were included for further quantitative analysis. Mean Cq differences between individual and corresponding pool samples ranged from 0.1 Cq (Cr.I. -0.98 to 1.17) to 2.09 Cq (Cr.I. 1.24 to 2.94). Overall, 19,535 asymptomatic and presymptomatic patients were screened using 4,400 RT-qPCR assays, resulting in 246 positive patients (positivity rate 1.26%). This corresponds to an increase of 4.4 times in laboratory capacity and a reduction of 77% in required tests. Finally, these data demonstrate that swab pooling can significantly minimize sample dilution and sensitivity issues commonly seen in its traditional counterpart. Therefore, swab pooling represents a major alternative for reliable and large-scale screening of SARS-CoV-2 in low prevalence populations.