Time-series Analysis of Combined Sewer Overflows and Gastrointestinal Illness in Atlanta, 2002 to 2013 Open Access
Miller, Alyssa (Spring 2020)
Abstract
Background: Combined sewer overflows (CSOs) discharge untreated sewage into surface water, often following periods of heavy precipitation, elevating concentrations of potentially pathogenic microorganisms. Given the projected increase in frequency and severity of precipitation in the southeastern United States, it is important to understand the health impacts of CSOs to inform adaptation practices. For the period 2002-2013, this study estimated associations of CSO events and emergency department (ED) visits for gastrointestinal (GI) illness among Atlanta residents, and investigated neighborhood-level poverty as a potential effect modifier.
Methods: Associations were estimated using Poisson generalized linear models, controlling for time trends. CSO events were categorized as high, medium, or low based on overflow volume and summarized by week to assess the effect of any CSO event in the week prior to the ED visits. We also considered the effect of CSO events at a two- and three-week lag. Models controlling for precipitation were compared to unadjusted models to evaluate confounding by precipitation. Effect modification by ZIP Code Tabulation Area (ZCTA)-level (neighborhood) poverty was evaluated with the inclusion of an interaction term.
Results: In the city-wide analysis, occurrence of a high volume CSO event in the previous week was associated with daily ED visits for GI illness, independent of the effects of precipitation. We identified a significant interaction by ZCTA-level poverty, observing stronger CSO-GI illness associations in areas with low poverty (percent of residents living in poverty below the median) compared to areas with high poverty. Among areas with low poverty, we observed associations at both one-week and longer lags, following high volume as well as lower volume CSO events; comparatively, among areas with high poverty, we observed associations only at a one-week lag, following high volume events.
Conclusions: Our findings suggest CSO events in Atlanta contribute to the burden of acute GI illness for city residents, and the magnitude of this risk may be higher among populations living in areas with low poverty. Given the consistent, positive associations following high volume events, avoiding exposure to surface water in the weeks following these events may reduce risk of GI illness. Moreover, when considering the projected impact of climate change in the region, future infrastructure projects should aim to reduce volume of CSO discharges.
Table of Contents
Background………………………………………………………………………………. 1
Methods…………………………………………………………………………………... 5
Results………………………………………………………………………………......... 9
Discussion………………………………………………………………………………. 14
References………………………………………………………………………………. 20
Tables………………………………………………………………………………........ 24
Figures………………………………………………………………………………....... 29
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Time-series Analysis of Combined Sewer Overflows and Gastrointestinal Illness in Atlanta, 2002 to 2013 () | 2020-04-29 12:14:58 -0400 |
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