Validation of the bag-mediated filtration system for environmental surveillance of poliovirus in Nairobi, Kenya

Abstract

AIMS : This study compared the bag-mediated filtration system (BMFS) and standard WHO two-phase separation methods for poliovirus (PV) environmental surveillance, examined factors impacting PV detection and monitored Sabin-like (SL) PV type 2 presence with withdrawal of oral polio vaccine type 2 (OPV2) in April 2016. METHODS AND RESULTS : Environmental samples were collected in Nairobi, Kenya (Sept 2015–Feb 2017), concentrated via BMFS and two-phase separation methods, then assayed using the WHO PV isolation algorithm and intratypic differentiation diagnostic screening kit. SL1, SL2 and SL3 were detected at higher rates in BMFS than two-phase samples (P < 0 05). In BMFS samples, SL PV detection did not significantly differ with volume filtered, filtration time or filter shipment time (P > 0 05), while SL3 was detected less frequently with higher shipment temperatures (P = 0 027). SL2 was detected more frequently before OPV2 withdrawal in BMFS and two-phase samples (P < 1 9 10 5). CONCLUSIONS : Poliovirus was detected at higher rates with the BMFS, a method that includes a secondary concentration step, than using the standard WHO two-phase method. SL2 disappearance from the environment was commensurate with OPV2 withdrawal. SIGNIFICANCE AND IMPACT OF THE STUDY : The BMFS offers comparable or improved PV detection under the conditions in this study, relative to the twophase method.