Optimal size of sample pooling for RNA pool testing: an avant-garde for scaling up SARS CoV 2 testing

IntroductionTimely diagnosis is essential for the containment of the disease and breaks in the chain of transmission of SARS-CoV-2. The present situation demands countries to scale up their testing and design innovative strategies to conserve diagnostic kits and reagents. The pooling of samples saves time, manpower, and most importantly diagnostic kits and reagents. In the present study, we tried to define the pool size that could be applied with acceptable confidence for testing. Material and methodsWe used repeatedly tested positive clinical sample elutes having different levels of SARS CoV 2 RNA and negative sample elutes to prepare seven series of 11 pools each, having pool sizes ranging from 2 to 48 samples to estimate the optimal pool size. Each pool had one positive sample elute in different compositions. All the pools were tested by SARS CoV 2 RT-qPCR. ResultsOut of the 77 pools, only 53 (68.8%) were found positive. The sensitivity of pools of 2 to 48 samples was decreased from 100% (95% CL; 98.4-100) to 41.41% (95% CL; 34.9-48.1). The maximum size of the pool with acceptable sensitivity (>95%) was found to be of 6 samples. For the pool size of 6 samples, the sensitivity was 97.8% and the efficiency of pooling was 0.38. ConclusionThe pooling of samples is a practical way for scaling up testing and ultimately containing the further spread of the COVID-19 pandemic.

Pooled RNA sample reverse transcriptase real time PCR assay for SARS CoV-2 infection: a reliable, faster and economical method.

BackgroundCorona virus disease 2019 (COVID-19) which initially started as a cluster of pneumonia cases in the Wuhan city of China has now become a full blown pandemic. Timely diagnosis of COVID-19 is the key in containing the pandemic and breaking the chain of transmission. In low and middle income countries availability of testing kits has become the major bottle neck in testing. Novel methods like pooling of samples are the need of the hour. MethodExtracted RNA samples were randomly placed in pools of 8 on a 96 well plate. Both individual RNA (ID) and pooled RNA RT-qPCR for the screening E gene were done in the same plate and the positivity for the E gene was seen. ResultsThe present study demonstrated that pool testing with 8 RNA samples can easily detect even up to a single positive sample with Ct value as high as 38. The present study also showed that the results of pool testing is not affected by number of positive samples in a pool. ConclusionPooling of 8 RNA samples can reduce the time and expense by one eighth, and can help expand diagnostic capabilities, especially during constrained supply of reagents and PCR kits for the diagnosis of SARS-CoV-2 infection.