What is the link between sewage contamination and waterborne disease incidence in high-income countries? A scoping review

Sewage contamination in high-income countries poses a serious public health concern due to the increased frequency of combined and sanitary sewer overflows. This might be due to aging infrastructure, climate change-driven extreme weather events, and insufficient regulatory enforcement. These events result in the discharge of untreated sewage into drinking and recreational waters, introducing pathogenic microorganisms that elevate the risk of gastrointestinal and other waterborne diseases, even in regions with advanced sanitation systems. This scoping review aims to map the evidence linking sewage overflows with waterborne disease incidence in high-income countries and to explore contributing structural (e.g., infrastructure failure, policy gaps) and environmental factors (e.g., extreme weather events). Literature searches were conducted across six databases and four grey literature sources, identifying 434 records. After screening and eligibility assessment, 20 studies published between 2007 and 2024 were included. The findings consistently associate combined sewer overflow events and water distribution system failures with elevated risks of gastrointestinal illness. High-volume sewage discharges following extreme rainfall were strongly linked to increased emergency room visits and outbreak incidence, with dose-response relationships observed in several studies, adding biological plausibility to these associations. However, the strength of this evidence must be interpreted with caution, as the majority of included studies were observational in design, limiting causal inference. Monitoring studies also revealed the presence of fecal indicator bacteria, viruses, protozoa, and antibiotic-resistant pathogens in affected water bodies. Underreporting of sewage spills and waterborne disease outbreaks emerged as a widespread limitation, impeding accurate public health risk assessment. Despite the availability of modern sanitation technologies, many high-income countries face persistent challenges due to deferred infrastructure upgrades and weak compliance mechanisms. This review emphasizes the importance of strengthening surveillance, implementing real-time water quality monitoring, and coordinating policy and infrastructure actions to mitigate sewage-related waterborne diseases resulting from inadequate wastewater management and changing environmental conditions.