Real-time public health interventions driven by wastewater and environmental surveillance during Uganda's 2025...

Mass gatherings increase the risk of infectious disease transmission, particularly when healthcare systems are overstretched and underfunded. Wastewater and environmental surveillance (WES) offer a real-time, non-invasive method for monitoring pathogen circulation at the population level. During Uganda's 2025 Martyrs' Day pilgrimage, which drew over three million people, the Ministry of Health used WES to identify and respond to health threats.

During the four days (May 31-June 3, 2025), 44 environmental samples were collected from 11 strategically selected sites, including wastewater manholes, septic tanks, stagnant surface water, and sacred water sources at both Catholic and Anglican shrines in Namugongo, Uganda. Samples were analyzed for multiple enteric and respiratory pathogens, including Mpox, using quantitative PCR (qPCR). Findings from this real-time surveillance directly triggered targeted, site-specific public health interventions during the mass gathering.

All sacred water sources and National Water and Sewage Corporation (NWSC) stand posts remained pathogen-free, and some pilgrims were observed drinking from them. In contrast, wastewater and stagnant surface water harbored multiple pathogens, predominantly non-O1/O139 Vibrio cholerae (36.4%) and Shigella spp. (31.8%), and Rotavirus A and Enterovirus (22.7% each). Notably, on Day 1, the detection of Salmonella spp. and Shigella spp. in a stagnant pool two meters from the Catholic Sacred Martyrs' Lake prompted immediate drainage and chlorination. On the same day, the identification of multiple enteric pathogens in Anglican Septic Tank 2, located beneath a food-vending zone, prompted septic tank emptying, vendor relocation, and strict food safety enforcement. These findings also triggered rapid WASH upgrades, multilingual community risk communication, and deployment of on-site clinical screening posts. Pathogen diversity peaked on Day 4 (June 3, Martyrs' Day), with the first detections of SARS-CoV-2, Mpox virus, Rotavirus C, and RSV.

This study demonstrates the first real-time use of WES to guide public health action during a major mass gathering in Sub-Saharan Africa. The detection of multiple pathogens, mapped by site and time, demonstrated the utility of WES as an early-warning indicator for mass gatherings. The site-specific data enabled rapid interventions, including Water, Sanitation, and Hygiene (WASH) infrastructure upgrades, draining stagnant pools, relocating food vendors, and on-site clinical screening, which likely reduced outbreak risks. These results show how WES can strengthen surveillance and support proactive public health responses at mass gatherings.

This first real-time WES deployment during a Sub-Saharan mass gathering demonstrates its value for early detection, rapid response, and multi-pathogen surveillance. The effective use of surveillance data to trigger coordinated, multi-agency interventions underscores WES as a vital component of mass-gathering preparedness within global health security frameworks.