Combined Sewer Overflows and Gastrointestinal Illness in Atlanta, 2002–2013: Evaluating the Impact of Infrastructure Improvements

Abstract

Background: Combined sewer overflows (CSOs) discharge untreated sewage into surface and recreational water, often following heavy precipitation. Given projected increases in frequency and intensity of precipitation due to climate change, it is important to understand the health impacts of CSOs and mediating effects of sewerage systems. Objectives: In this study we estimate associations of CSO events and emergency department (ED) visits for gastrointestinal (GI) illness among City of Atlanta, Georgia, residents and explore how these associations vary with sewerage improvements. Methods: We estimate associations using Poisson generalized linear models, controlling for time trends. We categorized CSOs by overflow volume and assessed effects of CSO events prior to ED visits with 1-, 2- and 3-wk lags. Similarly, we evaluated effects of weekly cumulative precipitation greater than the 90th percentile at the same lags. We also evaluated effect modification by ZIP Code Tabulation Area (ZCTA)-level poverty and infrastructure improvement period using interaction terms. Results: Occurrence of a large volume CSO in the previous week was associated with a 9% increase in daily ED visits for GI illness. We identified significant interaction by ZCTA-level poverty, with stronger CSO–GI illness associations in low than high poverty areas. Among areas with low poverty, we observed associations at 1-wk and longer lags, following both large and lower volume CSO events. We did not observe significant interaction by infrastructure improvement period for CSO– nor precipitation–GI illness associations; however, the number of CSO events decreased from 2.31 per week before improvements to 0.49 after improvements. Discussion: Our findings suggest that CSOs contribute to acute GI illness burden in Atlanta and that the magnitude of this risk may be higher among populations living in areas of low poverty. We did not find a protective effect of sewerage system improvements. Nonetheless, observed reductions in CSO frequency may lower the absolute burden of GI illness attributable to these events. https://doi.org/10.1289/EHP10399

Association between combined sewer overflow events and gastrointestinal illness in Massachusetts municipalities with and without river-sourced drinking water, 2014-2019

“…These findings are consistent with previous studies that found significant associations between sewage discharge events and AGI over lag periods from 2-8 days. [30][31][32][33] A four-day lag period is also consistent with the incubation times of some of the pathogens found in waterways contaminated with sewage. 1,9,47 Some AGI-causing viral and bacterial pathogens have incubation periods that are consistent with the short lag identified in this study including noroviruses (12-48 hours), rotavirus (1-3 days), Shigella (12 hours-7 days), and enterotoxigenic E. coli (12-72 hours).…”

“…Our findings suggest that a nonlinear dose-response relationship exists between upstream CSO discharge volume and AGI, a finding consistent with previous studies. 31,32 Miller et al…”

“…similarly found that only large CSO events (>75 th percentile CSO events by volume, equivalent to 56.5 MG) were significantly associated with AGI in the week following an event, but models estimating the association between any CSO event and AGI resulted in no association. 32 Jagai et al found that only the most extreme precipitation events (99 th percentile, equivalent to 1.97 in)…”

“…33 In all studies, the association between discharge events and reported AGI has a lag of two to eight days, which could be due to pathogen travel time in the waterbody, timing of recreational activity, drinking water treatment and distribution, pathogen infection and incubation, and/or decision to seek care. [30][31][32][33] .…”

Smart management of combined sewer overflows: From an ancient technology to artificial intelligence

“…CSO increases the concentration of pathogens, toxic substances, bacteria, solids, and debris in the receiving water bodies (McGinnis et al, 2022; Miller Alyssa et al, 2022; Whelan et al, 2022). Moreover, as a result of the decrease in the oxygen level due to the degradable organic matter, it creates important public health, aquatic organism stress, and water quality concerns (Bohannon & Lin, 2005; Field, 1985; House et al, 1993; Mailhot et al, 2015).…”