Water and sewage systems, socio-demographics, and duration of residence associated with endemic intestinal infectious diseases: a cohort study.

BACKGROUND: Studies of water-related gastrointestinal infections are usually directed at outbreaks. Few have examined endemic illness or compared rates across different water supply and sewage disposal systems. We conducted a cohort study of physician visits and hospitalizations for endemic intestinal infectious diseases in a mixed rural and urban community near Vancouver, Canada, with varied and well-characterized water and sewage systems. METHODS: Cohort members and their disease events were defined via universal health insurance data from 1995 through 2003. Environmental data were derived from municipal, provincial, and federal government sources. Logistic regression was used to examine associations between disease events and water and sewage systems, socio-demographic characteristics, and temporal factors. RESULTS: The cohort included 126,499 individuals and approximately 190,000,000 person-days. Crude incidence rates were 1,353 physician visits and 33.8 hospitalizations for intestinal infectious diseases per 100,000 person-years. Water supply chlorination was associated with reduced physician visit incidence (OR: 0.92, 95% CI 0.85-1.0). Two water systems with the highest proportions of surface water had increased incidence (ORs: 1.57, 95% CI 1.39-1.78; and 1.45, 95% CI 1.28-1.64). Private well water and well depth were not associated with increased risk, likely because of residents' awareness of and attention to water quality. There was increased crude incidence with increasing precipitation in the population served by surface water supplies, but this trend did not remain with adjustment for other variables. Municipal sewer systems were associated with increased risk (OR: 1.26, 95% CI 1.14-1.38). Most socio-demographic variables had predicted associations with risk: higher rates in females, in the very young and the elderly, and in residents of low income areas. Increased duration of area residence was associated with reduced risk (OR, duration ≥ 6 years: 0.69, 95% CI 0.60-0.80 vs. < 1 year: 1.16, 95% CI 1.03-1.30). CONCLUSIONS: This large cohort study, with objective data on exposures and outcomes, demonstrated associations between endemic infectious intestinal diseases and factors related to water supply, sewage disposal, socio-demographics, and duration of residency. The results did not always follow prior expectations based on studies examining outbreaks and single systems, and underscore the importance of studying factors associated with endemic disease across water and sewage system types.

Where's the pump? Associating sporadic enteric disease with drinking water using a geographic information system, in British Columbia, Canada, 1996-2005.

We investigated whether risk of sporadic enteric disease differs by drinking water source and type using surveillance data and a geographic information system. We performed a cross-sectional analysis, at the individual level, that compared reported cases of enteric disease with drinking water source (surface or ground water) and type (municipal or private). We mapped 814 cases of campylobacteriosis, cryptosporidiosis, giardiasis, salmonellosis and verotoxigenic Escherichia coli infection, in a region of British Columbia, Canada, from 1996 to 2005, and determined the water source and type for each case's residence. Over the 10-year period, the risk of disease was 5.2 times higher for individuals living on land parcels serviced by private wells and 2.3 times higher for individuals living on land parcels serviced by the municipal surface/ground water mixed system, than the municipal ground water system. Rates of sporadic enteric disease potentially differ by drinking water source and type. Geographic information system technology and surveillance data are accessible to local public health authorities and used together are an efficient and affordable way to assess the role of drinking water in sporadic enteric disease.