Sewer Overflows as Pathogen Vectors: A Systematic Review and Meta-Analysis of Pathogen Hazards, Influencing Factors, and Recommendations for Policy and Practice

The pathogen hazards and public health risks posed by sanitary and combined sewer overflows (SSOs and CSOs) around the world are not well understood. In this systematic review, we aimed to 1) characterize the pathogens present in sewer networks and during overflows; 2) highlight evidence linking sewer overflows to public health risks; 3) explore how sewer maintenance and management practices, user practices, and climate variability influence overflows; and 4) propose recommendations for policy and practice. Following PRISMA guidelines, we retrieved 9,677 studies from four peer-reviewed databases and included 48 studies in the final analysis. Most studies assessed fecal indicators (e.g., E. coli, fecal coliforms) (n = 35, 73%), evaluated CSOs rather than SSOs (n = 33, 69%), and were conducted in high-income countries (n = 43, 90%), highlighting a lack of research characterizing pathogens sewers in low- and middle-income countries. Key drivers of overflows included aging systems and poor quality of construction, lack of regular water supply, unreliable electricity, faulty connections, lack of proper solid waste management, and heavy rainfall and high groundwater tables. There is an urgent need for sanitation stakeholders to move beyond simply expanding sewer coverage, and equal emphasis must be placed on the ongoing operation and maintenance of these systems.