Abstract
Observational studies have assessed endemic waterborne risks in a number of countries. Time-series analyses associated increased water turbidity with increased gastroenteritis risks in several public water systems. Several cohort studies reported an increased risk of gastroenteritis in populations using certain public or individual water systems. Although several case-control studies found increased waterborne risks, they also found increased risks associated with other exposures. An increased risk of campylobacteriosis was associated with drinking untreated water from non-urban areas and some tap waters; other significant risks included contaminated poultry and foreign travel. Increased risks of cryptosporidiosis and giardiasis were associated with drinking water in some populations; other risk factors included foreign travel, day care exposures, and swimming. These observational studies provide evidence that some populations may be at an increased risk of endemic or sporadic illness from waterborne exposures, but not all studies found an increased risk. Differences in waterborne risks may be due to differences in water quality. System vulnerabilities and contamination likely differed in the areas that were studied. The information from these studies may help inform estimates of waterborne illness for the US population but is inadequate to estimate a population attributable risk.
Highlights
We evaluated the available information about endemic waterborne risks from cohort, case-control, time-series, and ecologic studies conducted in the United States and other developed countries
A study in seven states of the United States found that municipal water systems or well water was not associated with cryptosporidiosis risk among immnuocompetent persons; international travel, contact with cattle, contact with persons 2 – 11 years of age with diarrhea, and freshwater swimming were important risk factors
An increased risk of endemic waterborne disease has been epidemiologically associated with some drinking water sources and their treatment. These studies provide evidence that some populations using public or non-public drinking water systems may be at increased risk of endemic or sporadic illness
Summary
We evaluated the available information about endemic waterborne risks from cohort, case-control, time-series, and ecologic studies conducted in the United States and other developed countries. A high prevalence of the private, individual wells (20% of households) were contaminated with coliforms or E. coli above the standards, the study found no statistically significant associations between these indicator bacteria and AGI. As part of a population-based prospective survey to determine the incidence of AGI during 1999 and 2000, Kuusi et al (2003) collected information about selected exposures, including drinking water. Among children less than 15 years of age, drinking water from a private, individual water system (well or surface source) was associated with an increased illness risk (RR 1⁄4 3.1; 95% CI 1⁄4 1.4– 7.1) while using chlorinated water was protective (RR 1⁄4 0.4; 95% CI 1⁄4 0.2– 0.9). Fraser & Cooke (1991) found that the incidence of laboratory-confirmed giardiasis was higher (RR 1⁄4 3.3; 90% CI 1⁄4 1.1– 10.1) in an area of Dunedin where surface water was mechanically microstrained through a 23 mm screen and chlorinated compared to other areas where drinking water was more thoroughly treated (i.e. coagulation, flocculation, dual media filtration, and chlorination)
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