Lessons from applied large-scale pooling of 133,816 SARS-CoV-2 RT-PCR tests

Pooling multiple swab samples prior to RNA extraction and RT-PCR analysis was proposed as a strategy to reduce costs and increase throughput of SARS-CoV-2 tests. However, reports on practical large-scale group testing for SARS-CoV-2 have been scant. Key open questions concern reduced sensitivity due to sample dilution; the rate of false positives; the actual efficiency (number of tests saved by pooling) and the impact of infection rate in the population on assay performance. Here we report analysis of 133,816 samples collected at April-September 2020, tested by pooling for the presence of SARS-CoV-2. We spared 76% of RNA extraction and RT-PCR tests, despite the reality of frequently changing prevalence rate (0.5%-6%). Surprisingly, we observed pooling efficiency and sensitivity that exceed theoretical predictions, which resulted from non-random distribution of positive samples in pools. Overall, the findings strongly support the use of pooling for efficient large high throughput SARS-CoV-2 testing.

Pooled RNA extraction and PCR assay for efficient SARS-CoV-2 detection

Testing for active SARS-CoV-2 infection is a fundamental tool in the public health measures taken to control the COVID-19 pandemic. Due to the overwhelming use of SARS-CoV-2 RT-PCR tests worldwide, availability of test kits has become a major bottleneck. Here we demonstrate pooling strategies to perform RNA extraction and RT-PCR in pools, significantly increasing throughput while maintaining clinical sensitivity. We implemented the method in a routine clinical diagnosis setting of asymptomatic populations, and already tested 5,464 individuals for SARS-CoV-2 using 731 RNA extraction and RT-PCR kits. We identified six SARS-CoV-2 positive patients corresponding to 0.11% of the tested population.