The Sonoma Water Evaluation Trial: A Randomized Drinking Water Intervention Trial to Reduce Gastrointestinal Illness in Older Adults

Objectives. We estimated the relative rate of highly credible gastrointestinal illness (HCGI) per year associated with active versus sham household water filtration devices among older adults in a community receiving tap water meeting current US standards.Methods. We conducted a randomized, triple-blinded, crossover trial in 714 households (988 individuals), which used active and sham water filtration devices for 6 months each. We estimated the annual incidence rate ratio of HCGI episodes and the longitudinal prevalence ratio of HCGI days at population and individual levels with a generalized estimating equation (GEE) and generalized linear mixed models (GLMMs), respectively, adjusted for covariates associated with outcome.Results. The incidence rate ratios (active versus sham) were 0.88 (95% confidence interval [CI] = 0.77, 1.00) and 0.85 (95% CI = 0.76, 0.94) HCGI episodes per year estimated by GEE and GLMM models, respectively. The corresponding longitudinal prevalence ratios were 0.88 (95% CI = 0.74, 1.05) and 0.84 (95% CI = 0.78, 0.90) HCGI days per person per year.Conclusions. We observed reductions in population- and individual-level measures of HCGI associated with use of the active filtration device. These findings suggest the need for further research on the impact of drinking water on the health of sensitive subpopulations.Widespread outbreaks of gastrointestinal infectious illness have occurred in the United States at times when public water treatment systems have failed.^1,2 This has led to intense public interest in whether the microbial content of drinking water might present a health risk even when public water treatment systems are believed to be functioning properly.^3–5Several randomized intervention trials with supplemental in-home drinking water treatment have been reported in general populations^6–10; none focused on older individuals. Estimates of the annual number of cases of acute gastrointestinal illness related to drinking water in the United States, drawn from a variety of data sources and study designs, vary from 1.8 million to 16.4 million cases per year in the general population.^11–13 The US Environmental Protection Agency has called attention to the differential burden of drinking water–related disease among those who may be at increased risk of infection and serious illness from exposure to microbial pathogens, such as the elderly, children, and persons who are immunocompromised by infection, malignancy, or chemotherapy.^14–16 Older adults may be particularly susceptible to gastrointestinal infections and to severe illness once infected.^17–19We conducted the first drinking water trial exclusively studying older adults (aged ≥ 55 years). The study, performed in Sonoma County, California, was a randomized, controlled, triple-blinded (participants, investigators, analysts), crossover intervention trial. Our goal was to estimate the efficacy of an in-home water filter to reduce the risk of highly credible gastrointestinal illness (HCGI) among older adults living in a community whose tap water met or exceeded current US drinking water standards.