Establishing a wastewater environmental surveillance network for enteropathogens in low-and middle-income countries – experience from Pakistan

Background: Wastewater surveillance has emerged as a powerful public
health tool for the early detection of pathogens and the monitoring of
community-level disease trends. This study aimed to establish and validate
the utility of an ES system in Karachi, Pakistan, for tracking diverse
pathogens to inform targeted public health actions. This manuscript
describes the methodology, process, and challenges encountered during the
establishment of an environmental surveillance network in Karachi.
Methods: A wastewater environmental surveillance (WES) study was
implemented in 3 towns in Karachi (Gadap, Lyari and Gulshan-e-Iqbal).
Teams manually traced drainage pathways, flow direction, and georeferenced
data. Sites were selected based on population catchment, absence of
industrial effluent, and logistical feasibility. From 2021-2023,
wastewater samples were collected using Bag Mediated Filtration System
(BMFS). Thirty two  sites were validated through sensitivity
analyses comparing wastewater detection of pathogens like Sabin
poliovirus, SARS-CoV-2, and S. typhi with clinical data.
Results: The mean ± SD duration of blue line tracing and mapping was 15.6
± 4.0 days for each town. In the first round, conducted during and after
the bOPV Supplemental Immunization Activity (SIA), 403 wastewater samples
from 12 ES sites in Gadap town were analyzed, showing low detection of
Sabin targets. Detection rates remained low in the second round during
which 232 wastewater samples from 28 WES sites in the 3 towns were
analyzed. In the third round, 32 287 wastewater samples from 32 WES sites
showed improved results with enhanced pathogen detection including
site-level SARS-CoV-2 and EV. We highlighted challenges that WES faces
such as field, laboratory and analytical including, logistical barriers
and environmental variability. Conclusion: We identified and validated 32
WES sites for the detection of enteropathogens in wastewater across three
towns in Karachi. The successful establishment of WES network was made
possible by strong collaboration with key stakeholders and experts.