Abstract
The nature and magnitude of endemic waterborne disease are not well characterized in the United States. Epidemiologic studies of various designs can provide an estimate of the waterborne attributable risk along with other types of information. Community drinking water systems frequently improve their operations and may change drinking water treatment and their major source of water. In the United States, many of these treatment changes are the result of regulations promulgated under the Safe Drinking Water Act. A community-intervention study design takes advantage of these "natural" experiments to assess changes in health risks. In this paper, we review the community-intervention studies that have assessed changes in waterborne gastroenteritis risks among immunocompetent populations in industrialized countries. Published results are available from two studies in Australia, one study in the United Kingdom, and one study in the United States. Preliminary results from two other US studies are also available. Although the current information is limited, the risks reported in these community-intervention studies can help inform the national estimate of endemic waterborne gastroenteritis. Information is provided about endemic waterborne risks for unfiltered surface water sources and a groundwater under the influence of surface water. Community-intervention studies with recommended study modifications should be conducted to better estimate the benefits associated with improved drinking water treatment.
Highlights
This paper examines the available data from communityintervention studies to help develop a national estimate of waterborne disease risk in the United States
The attributable risk (AR) for credible gastrointestinal illness (CGI) was calculated using {1⁄2pðRR 2 1Þ=1⁄2pðRR 2 1Þ þ 1} £ 100: The AR associated with unfiltered surface water is 34%; filtration resulted in a 34% reduction in CGI
What can community-intervention studies tell us about the incidence, prevalence, or risk of waterborne acute gastroenteritis illness (AGI) in the United States – quantitative or qualitative? Studies outside the United States considered cases identified by medical surveillance
Summary
Large populations may be required in observational studies to obtain sufficient statistical power to detect an association between endemic gastrointestinal illness and waterborne exposures, and observational studies may not be economically or technically feasible to assess small risks, especially when it is difficult to ascertain gradients in exposures to microorganisms in drinking water. Dramatic changes in waterborne microbial exposures may occur when water sources are changed or treatment is added (Craun 1988) Such an improvement in the microbial quality of drinking water should increase the probability that a community-intervention study will be able to detect a change in endemic illness, if one occurs. Water treatment changed from chlorination-only to a facility that used ozone, granular filtration, and chorination This was initially to be a pilot study, sufficient information was collected about water quality and health to assess waterborne gastroenteritis risks. The key endpoint of interest was credible gastrointestinal illness (CGI) defined as nausea and abdominal cramps; Table 1 | Summary of study designs
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