Pooled nasopharyngeal swab collection in a single vial for the diagnosis of SARS CoV-2 infection: An effective cost saving method

BACKGROUND: Pool testing is one of the strategy to expedite testing capacities while simultaneously conserving various diagnostic kits, reagents and consumables and time. In the present study, we investigated potential role of combined specimen collection technique for the diagnosis of SARS-CoV-2 virus infection where five nasopharyngeal swabs were collected from different individuals and pooled together in a single viral transport medium (VTM). MATERIAL AND METHODS: This pilot study was conducted on different cohorts of Delhi state. Two nasopharyngeal swabs were collected from each enrolled individual. One swab was put into VTM vial to be further used for individual swab testing (ID). The other swab was put into a fresh VTM for pool swab collection. Each pool comprised five swabs collected from five different patients in one VTM vial. Both IDs and pools were tested in parallel for the detection of SARS-CoV-2 using real time PCR. RESULTS: A total of 46 pools were collected from 230 enrolled individuals.Among 230 ID tested, 60 were found to be positive for both E and RdRp gene. Among 46 pools, 25 pools included all negatives samples and remaining 21 pools included one or more positives. Comparing ID with pool results, overall concordance was seen in 42 pools (91.3%). Four pools showed false positive results as all included samples on ID testing were found to be negative. Considering ID results as reference, swab pool showed 100% sensitivity, 84% specificity, 84% positive predictive value and 100% negative predictive value. CONCLUSION: The pooling of swab strategy could be beneficial only among asymptomatic in low prevalence areas.