Evaluation of the bag-mediated filtration system as a novel tool for poliovirus environmental surveillance: Results from a comparative field study in Pakistan

Abstract

Poliovirus (PV) environmental surveillance (ES) plays an important role in the global eradication program and is crucial for monitoring silent PV circulation especially as clinical cases decrease. This study compared ES results using the novel bag-mediated filtration system (BMFS) with the current two-phase separation method. From February to November 2016, BMFS and two-phase samples were collected concurrently from twelve sites in Pakistan (n = 117). Detection was higher in BMFS than two-phase samples for each Sabin-like (SL) PV serotype (p<0.001) and wild PV type 1 (WPV1) (p = 0.065). Seventeen sampling events were positive for WPV1, with eight discordant in favor of BMFS and two in favor of two-phase. A vaccine-derived PV type 2 was detected in one BMFS sample but not the matched two-phase. After the removal of SL PV type 2 (SL2) from the oral polio vaccine in April 2016, BMFS samples detected SL2 more frequently than two-phase (p = 0.016), with the last detection by either method occurring June 12, 2016. More frequent PV detection in BMFS compared to two-phase samples is likely due to the greater effective volume assayed (1620 mL vs. 150 mL). This study demonstrated that the BMFS achieves enhanced ES for all PV serotypes in an endemic country.

Feasibility of the Bag-Mediated Filtration System for Environmental Surveillance of Poliovirus in Kenya

“…The shipping and storage times and conditions may have affected the detection of PV. Finally, as only SL PV was detected in this study, additional evaluation in WPV endemic regions is necessary to show BMFS capacity to detect circulating WPV (Zhou et al 2018).…”

“…Training on a supplemental "bucket" modification was completed by telephone with a detailed illustrated protocol. This modification was developed to safely transport large water samples on cold chain for sites with safety or security concerns (Zhou et al 2018).…”

“…The filter was transported on cold packs to the KEMRI laboratory. Beginning in May 2015, filtration was completed at a manhole over a sewer conveyance line on the KEMRI campus rather than at the field site, with the implementation of the bucket modification as described elsewhere (Zhou et al 2018). Briefly, sample transport with the bucket modification included cold chain and water-tight secondary containment via a 5-gallon bucket with a water-tight lid.…”

“…After filtration, the samples are transported by reverse cold chain to the laboratory for further processing. In the laboratory, a preservative mixture is added to improve the survival of PV over time on the filters followed by filter elution and secondary concentration (Fagnant et al 2017(Fagnant et al , 2018Zhou et al 2018). Processing large volumes allows for an increased effective volume assayed, while on-site filtration eliminates transport of large water samples and reduces required laboratory space.…”

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

“…Consequently, the bag-mediated filtration system (BMFS) was developed to enable primary concentration of 3-6 l in the field, followed by secondary concentration in the laboratory. This method increased the concentration factor to 300-to 600-fold with a final volume of 10 ml (Fagnant et al 2014(Fagnant et al , 2018WHO 2015a;Zhou et al 2018). A previous study was conducted in Nairobi to identify and address complications from conducting a multi-national study, and compare PV detection between environmental samples concentrated by the two-phase method and BMFS, using a limited data set (Zhou et al 2018).…”