PATH Case Study

How bag-mediated filtration systems are revolutionizing environmental surveillance

May 31, 2023

Environmental surveillance plays a crucial role in monitoring and preventing infectious disease outbreaks. However, conventional methods are limited. The new bag-mediated filtration system is revolutionizing the environmental surveillance of pathogens for enteric viruses, particularly poliovirus.

Many remote, low-resource communities lack effective, affordable methods for detecting poliovirus, allowing it to circulate.
Bag-mediated filtration is a highly sensitive, easy-to-use system for environmental surveillance of pathogens.
Bangladesh, Kenya, Malawi, Nepal, Pakistan, Yemen, Zambia
Bill & Melinda Gates Foundation, Paul G. Allen Family Foundation
Path Expertise Areas

Prototype evaluation

Market research and commercialization

Product verification and validation


Monitoring, evaluation, and learning

Infectious diseases

Disease surveillance

The bag-mediated filtration system captures traces of the poliovirus in wastewater

The bag-mediated filtration system (shown above) is a highly sensitive, easy-to-use tool for the surveillance of pathogens. Photo: University of Washington/ Christa Fagnant-Sperati.

The challenge

While global efforts have brought us close to eradicating polio, the remaining challenge lies in identifying and eliminating hidden pockets of the disease before it spreads to other communities that are vulnerable to polio due to lack of vaccination. Clinical cases of polio are now rare and do not adequately indicate the risk of transmission. Polioviruses , including wild poliovirus type 1 and vaccine-derived polioviruses, can silently spread and go undetected for months.

Traditional environmental surveillance methods involve shipping 500 mL of wastewater samples under cold chain conditions, which incurs high costs, limits sample volume and poses biohazard risks. Additionally, in conflict zones where shipping disruptions are common, testing liquid samples becomes near impossible.

"If the global community hopes to eradicate wild polio soon, we’ll need stronger environmental surveillance methods. The BMFS can identify circulating viruses in a community and trigger responses to prevent outbreaks before they occur," says Dr. David Boyle, Laboratory Director of the Diagnostics program at PATH.

“If the global community hopes to eradicate wild polio soon, we’ll need stronger environmental surveillance methods. The BMFS can identify circulating viruses in a community and trigger responses to prevent outbreaks before they occur.”
— Dr. David Boyle, Laboratory Director, Diagnostics program

The solution

To address these challenges, PATH, in collaboration with the University of Washington, University of Pretoria, Kenya Medical Research Institute (KEMRI), the Pakistan National Institutes of Health/Polio Eradication Programme, the World Health Organization (WHO), and Scientific Methods, Inc., developed, validated, and commercialized the bag-mediated filtration system (BMFS). This innovative system collects and filters 6 liters of wastewater through a small filter that efficiently captures viruses. The filter unit can then be easily and safely shipped to a reference laboratory for processing, significantly reducing costs and biohazard risks.

Ensuring commercial access has been critical in translating the BMFS into a globally available tool to support poliovirus surveillance and eradication programs. PATH partnered with Scientific Methods Inc. to manufacture and supply BMFS kits to countries where poliovirus remains active. The BMFS has achieved "accepted" classification by the WHO Global Polio Laboratory Network, with its results reported globally.

The approach

The BMFS is a simple yet highly sensitive and user-friendly tool that can be deployed in various settings, including challenging environments such as conflict zones. Its sensitivity surpasses that of conventional environmental surveillance methods, enabling the detection of even low levels of poliovirus.

The BMFS has been successfully used in multiple countries, including Bangladesh, Malawi, Nepal, Pakistan, Yemen, and Zambia, to monitor the presence of polio and other pathogens. Notably, in a WHO lead study in Yemen, the BMFS demonstrated its capability of providing approximately one-month early warning of the presence of poliovirus before clinical cases were reported.

The BMFS consists of a collection bag and a small filtration unit. The collection bag is filled with approximately 6 liters of wastewater, and the BMFS filtration unit, equipped with a specialized filter, is connected to the bag. When the wastewater passes through, the filter captures viruses and safely discards the filtered liquid.

The filter containing the captured pathogens can be detached and shipped to a reference laboratory for further analysis. This innovative approach allows for the collection of viruses from a larger sample volume while addressing logistical challenges and biohazard risks associated with transporting liquid samples.

Environmental surveillance

A sampling team at a Pakistan processing site collects wastewater through the bag-mediated filtration system. PATH/ David Boyle.

The impact

The BMFS has proven to be an effective tool for environmental surveillance of pathogens, particularly in detecting polio and other enteroviruses. By using the BMFS, ministries of health and other public health partners are better able to detect pathogens and identify at-risk populations. They can then respond earlier, with supplementary immunization campaigns or other prevention methods, to flatten transmission curves as soon as possible.

This is particularly valuable in regions where the transport of samples is challenging. The BMFS streamlines that process and enables health systems and policymakers to implement timely public health measures before the disease peaks.

The results

The bag-mediated filtration system has emerged as a valuable tool for environmental surveillance of pathogens, revolutionizing the way we detect and monitor diseases like polio and other enteric viruses. Its simplicity and adaptability make it suitable for deployment in diverse settings, including challenging environments.

The BMFS offers a practical solution, enabling early detection and intervention to prevent outbreaks. As we move closer to eradicating polio and continue our fight against other infectious diseases, the BMFS stands as a testament to the power of innovative technologies in global health surveillance and response.


  • WHO Eastern Mediterranean Regional Office
  • GPLN
  • Kenya Medical Research Institute
  • Liverpool School of Tropical Medicine
  • Malawi Liverpool Wellcome Trust Clinical Research Programme
  • Pakistan National Institutes of Health
  • Scientific Methods Inc.
  • The Aga Khan University
  • University of Pretoria
  • University of Virginia
  • University of Washington
  • US CDC
  • WHO Global Polio Laboratory Network