Abstract
Amid polio eradication efforts, detection of oral polio vaccine (OPV) virus in stool samples can provide information about rates of mucosal immunity and allow estimation of the poliovirus reservoir. We developed a multiplex one-step quantitative reverse transcription-PCR (qRT-PCR) assay for detection of OPV Sabin strains 1, 2, and 3 directly in stool samples with an external control to normalize samples for viral quantity and compared its performance with that of viral culture. We applied the assay to samples from infants in Dhaka, Bangladesh, after the administration of trivalent OPV (tOPV) at weeks 14 and 52 of life (on days 0 [pre-OPV], +4, +11, +18, and +25 relative to vaccination). When 1,350 stool samples were tested, the sensitivity and specificity of the quantitative PCR (qPCR) assay were 89 and 91% compared with culture. A quantitative relationship between culture(+)/qPCR(+) and culture(-)/qPCR(+) stool samples was observed. The kinetics of shedding revealed by qPCR and culture were similar. qPCR quantitative cutoffs based on the day +11 or +18 stool samples could be used to identify the culture-positive shedders, as well as the long-duration or high-frequency shedders. Interestingly, qPCR revealed that a small minority (7%) of infants contributed the vast majority (93 to 100%) of the total estimated viral excretion across all subtypes at each time point. This qPCR assay for OPV can simply and quantitatively detect all three Sabin strains directly in stool samples to approximate shedding both qualitatively and quantitatively.