Diagnostic Performance of Pooled RT-PCR Testing for SARS-CoV-2 Detection

BackgroundWith the high number of COVID-19 cases, a need to optimize testing strategy must be regarded to obtain timely diagnosis for early containment measures. With this, several studies have employed pooled RT-PCR testing for SARS-CoV-2 as this could potentially conserve laboratory resources while has the capacity to test several individuals. However, this was recommended to firstly validate the method as different laboratory reagents and equipment vary with its diagnostic performance. ObjectiveThe aim of this study was to determine the diagnostic performance of pooled SARS-CoV-2 nasopharyngeal/oropharyngeal swabbed samples using RT-PCR technique. MethodsA records review of two-staged pooled RT-PCR testing data from August 10, 26, 30 and September 5, 2020 was utilized from Northern Mindanao Medical Center COVID-19 Satellite Laboratory (formerly CHDNM TB Regional Center). For the first stage, using known samples, a total of 30 pools were made for each of the pooling size, 5- and 10-pooled, on both pooling phase, pre- and post-RNA extraction. One positive individual was used to represent each of the Cycle threshold values given (<24, 25-28, 29-32, 33-36, and 37-40) while the rest of the samples were negative. For the second stage, 54 pools of five from 270 random unknown samples were used to validate the results. Target gene performance of N gene and RdRp was also determined. Key ResultsResults show that 5-pooled sample has higher sensitivity (SN), specificity (SP), positive predictive value (PPV), and negative predictive value (NPV) of 100% (95% confidence interval (CI) 88.97-100), 66.95% (95% CI, 60.75-72.6), 28.18% (95% CI, 20.62-37.22), and 100% (95% CI, 97.66-100) compared to 10-pooled sample that has 87.1% (95% CI, 71.15-94.87), 56.9% (50.57-63.02), 20.77% (95% CI, 14.68-28.53) and 97.14% (95% CI, 92.88-98.88). Further, these Ct values were only from the N gene, emphasizing its higher diagnostic performance as well to detect SARS-CoV-2 compared to RdRp as only a few samples were detected, thus, no analysis was made. ConclusionThis study found out that 5-pooled sample has better diagnostic performance compared to 10-pooled samples. Specifically, all positive individual samples were detected in 5-pooled samples in pre-RNA extraction phase which these results are evident and consistent on both known and unknown samples. N gene was found out to detect more SARS-CoV-2 samples compared to RdRp.