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

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.SUPPORTING INFORMATION: Appendix S1. Nairobi environmental surveillance sites. Appendix S2. Statistical methods. Appendix S3. Replicate BMFS samples. Appendix S4. Samples included in statistical analyses. Appendix S5. NPEV detection in BMFS and two‐phase samples.Funding was provided by the Paul G. Allen Foundation, Grant Number NPT.1938-603689, and the Bill and Melinda Gates Foundation, Grant Number OPP1170548. This work was supported in part by the UW NIEHS sponsored Biostatistics, Epidemiologic and Bioinformatic Training in Environmental Health (BEBTEH) Training Grant, Grant #: NIEHS T32ES015459. We would like to thank James Angawa, Public Health Surveillance Officer, Nairobi County and Pius Odhiambo, Community Health Volunteer, for their assistance sampling; Director of KEMRI for facilitating the study; Graciela Matrajt for her technical writing assistance; and Dan Phillips for his assistance with project coordination.The Paul G. Allen Foundation and the Bill and Melinda Gates Foundation.https://sfamjournals.onlinelibrary.wiley.com/journal/13652672am2020Medical Virolog