Case Study

Path & Bag-Mediated Filtration System

PATH and the University of Washington have developed, validated, and commercialised a new environmental surveillance tool to assist in the global eradication of poliovirus.[1] The bag-mediated filtration system (BMFS) collects wastewater in a bag, and then passes it by gravity through a simple filter that binds the poliovirus. The BMFS can sample volumes of up to 6 litres of wastewater. It offers higher sensitivity as it samples a large volume, and the small filters are easier to ship from remote and challenging environments than liquid samples. The use of preservatives on the filter reduces the need for immediate processing when the filters are received at a reference laboratory.[2] Furthermore, a method using skimmed milk flocculation can concentrate the 6 litres into a single pellet that can be resuspended into a liquid for testing.[3]

PATH selected Scientific Methods Incorporated ( as the commercial partner to supply kits at acceptable pricing to low- and middle-income countries, especially those where poliovirus remains active.[4]

Tools such as the BMFS can also support monitoring for other enteric viruses, with similar advantages for biosafety, sampling volume, and ease of use.[5] A new field of critical interest includes the implementation of the BMFS for SARS-CoV-2 virus detection to assess its persistence and distribution within communities to inform on asymptomatic reservoirs as transmission risks, especially for areas where in-person testing is highly limited or absent.[6]

[1] Zhou, N. A., Fagnant-Sperati, C. S., Shirai, J. H., Sharif, S., Zaidi, S. Z., Rehman, L., Hussain, J. et al. (2018). Evaluation of the bag-mediated filtration system as a novel tool for poliovirus environmental surveillance: results from a comparative field study in Pakistan. PloS ONE 13(7), e0200551,


[2] “New Tool Detects Poliovirus Hiding in the Environment.” 2020.


[3] Falman, J. C., Fagnant-Sperati, C. S., Kossik, A. L., Boyle, D. S., Meschke, J. S. (2019). Evaluation of secondary concentration methods for poliovirus detection in wastewater. Food and Environmental Virology 11(1), 20–31,


[4] Ibid.

[5] Van Zyl, W. B., Zhou, N. A., Wolfaardt, M., Matsapola, P. N., Ngwana, F.B., Symonds, E. M. et al. (2019). Detection of potentially pathogenic enteric viruses in environmental samples from Kenya using the bag-mediated filtration system. Water Supply, 19(6), 1668–76,


[6] “New Tool Detects Poliovirus Hiding in the Environment.” 2020.

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