The efficiency of selective pooling strategy in a COVID-19 diagnostic laboratory

Mass testing is essential in the surveillance strategy for fighting the COVID-19 pandemic. It allows early detection of suspected cases and subsequently early isolation to mitigate spread. However, the high cost and limited consumables and reagents hinder the mass testing strategy in developing countries such as Indonesia. The specimen pooling strategy is an option to perform mass screening with limited resources. This study aims to determine the positivity rate cut-off and to evaluate the efficiency of pooling strategy for the laboratory diagnosis of COVID-19.

Between August 4th, 2020, and November 11th, 2020, a four-sample pooling strategy testing to detect SARS-CoV-2 was carried out at the Microbiology Diagnostic Laboratory of Diponegoro National Hospital, Semarang, Indonesia. Pools with positive results were subjected to individual specimen retesting. Spearman's correlation and linear regression analysis were used to determine the best positivity rate cut-off to apply pooling strategy.

A total of 15,216 individual specimens were pooled into 3,804 four-sample pools. Among these pools, 1,007 (26.47%) were positive. Five hundred and ten (50.64%) were 1/4 positive. A maximum positivity rate of 22% is needed to save at least 50% extraction and qRT-PCR reactions in a four-sample pooling strategy. CT values between individual specimens and pools showed a good interval agreement.

Pooling strategy could reduce personnel workload and reagent cost, and increase laboratory capacity by up to 50% when the positivity rate is less than 22%.