A Review of Combined Sewer Overflows and Gastrointestinal Illness in a Changing Climate

During a combined sewer overflow (CSO) event, the capacity of a sewer system is exceeded, and untreated sewage, wastewater, and stormwater are released into nearby water bodies. CSOs occur in urban areas due to heavy precipitation, which is expected to occur more frequently and at higher intensity in certain regions of the world due to increasing climate variability. After a CSO, humans can be exposed to pathogens through recreational activities and contaminated drinking water. While previous research has quantified the impacts of CSOs on water quality indicator species and described the effects of CSOs on coastal wetland ecosystems, there is limited research on the potential human health impacts of CSOs. We conducted a literature search of peer-reviewed epidemiological studies that investigated associations between CSOs and human health outcomes.

Our literature search and screening methods returned eight studies on the association between CSOs and gastrointestinal (GI) illness in Europe and North America. Our selected peer-reviewed publications included five different study designs: time series, case-crossover, retrospective cohort, case-control, and case time series, with study periods including years 2002 to 2019.

The included studies showed evidence of a positive association between CSOs and GI illness, and one study suggested that sewer infrastructure improvements may decrease the burden of GI illness in future decades.