Drinking Water Travel Time and Emergency Department Visits for Gastrointestinal Illness

Abstract

ISEE-321 Objective: Aging pipe networks used to distribute treated drinking water in the United States are playing an increasing role in infectious disease outbreaks, and the potential for endemic disease transmission by this route is substantial. Water travel time, the time it takes for water to travel from the treatment plant to the end user, can serve as an indicator of the potential for distribution system contamination. It can be estimated using hydraulic models, which incorporate pipe layout, size, and flow. This analysis examined whether the average water travel time for a zip code is related to the proportion of emergency department (ED) visits for gastrointestinal (GI) illness in that zip code. Material and Methods: ED data were collected from all hospitals within a major US city from 1996 to 2003. One of the largest water utilities in the city, serving 650,000 people, was considered. People served by the utility had 1,315,040 total visits; 72,759 (5.5%) for GI illness. The relationship between water travel time and GI illness risk was assessed using logistic regression, controlling for potential confounding factors, including age, season, year, hospital, distance from zip code to hospital, and indicators of SES. Results: The risk ratio for travel time treated as a continuous variable suggested little or no association. However, the risk ratio for residents of zip codes in the top decile of water travel times compared with residents of zip codes in the lowest decile of water travel times suggested modestly increased risk (risk ratio = 1.07, 95% confidence interval = 1.02–1.14). Effect modification by year was also suggested. Conclusions: These preliminary results suggest a possible contribution of drinking water distribution system contamination to the burden of GI illness. Future analyses will use water travel time estimates from additional utilities in the study area.