摘要：Objectives. This study investigated if the type of drinking water source (treated municipal, untreated municipal, and private well water) modifies the effect of hydrology on childhood (aged < 5 years) gastrointestinal illness. Methods. We conducted a time series study to assess the relationship between hydrologic and weather conditions with childhood gastrointestinal illness from 1991 to 2010. The Central and Northern Wisconsin study area includes households using all 3 types of drinking water systems. Separate time series models were created for each system and half-year period (winter/spring, summer/fall). Results. More precipitation (summer/fall) systematically increased childhood gastrointestinal illness in municipalities accessing untreated water. The relative risk of contracting gastrointestinal illness was 1.4 in weeks with 3 centimeters of precipitation and 2.4 in very wet weeks with 12 centimeters of precipitation. By contrast, gastrointestinal illness in private well and treated municipal areas was not influenced by hydrologic conditions, although warmer winter temperatures slightly increased incidence. Conclusions. Our study suggests that improved drinking water protection, treatment, and delivery infrastructure may improve public health by specifically identifying municipal water systems lacking water treatment that may transmit waterborne disease. Contaminated drinking water is responsible for a widespread disease burden in developed countries. 1 Exposure analysis and field studies in the United States estimate gastrointestinal illness (GI) attributable to drinking water in the range of 2 to 19 million cases per year. 2,3 Measuring this disease burden is difficult because GI produces a broad spectrum of symptoms, specific tests are rarely conducted to determine etiology, and most infected people do not seek medical treatment. Compared with the general population, children are most commonly infected with enteric pathogens and may suffer more severe health consequences. In the United States, regulations and treatment practices differ by drinking water source (surface, ground) and by water system type (public municipal, private well). The federal Safe Drinking Water Act and Groundwater Rule mandate municipal ground and surface water monitoring and surface water treatment. Community municipal water systems without water treatment tend to have higher rates of waterborne disease. 4,5 Water treatment refers to multiple methods (coagulation, flocculation, sedimentation, filtration, primary and secondary disinfection) that may be combined to remove pathogens. 6,7 Treatment sanitizes, filters, or inactivates most pathogens. However, pathogens that survive treatment or infiltrate finished water distribution systems cause a sizeable GI burden. 3,8,9 There are no federal regulations for private well water quality. Some states require water quality testing when houses are being bought or sold. Roughly 104 million people in the United States rely on groundwater. 10 Groundwater accounted for 61% of documented US drinking water–borne disease outbreaks during 2007 and 2008. 11 There is an increasing recognition that groundwater can be contaminated by human viruses. 12 Soil layers incompletely “filter” miniscule (25–90 nm) viruses. The waterborne disease burden may be widespread but is difficult to identify with existing public health surveillance systems. 3 Enhanced knowledge of processes that degrade drinking water quality may augment surveillance activities. Hydrologic events may transport pathogens to drinking water sources or overwhelm sewage or drinking water infrastructure. Most documented North American waterborne disease outbreaks are preceded by extreme rainfall events. 13,14 In fact, communities that are primarily served by minimally treated drinking water may record elevated GI incidence during these hydrologic events. 15,16 Snowmelt or extreme precipitation may cause combined sewer overflow events, which also increase GI rates. 17 Assuming drinking water is the primary exposure route to waterborne pathogens, GI rates are likely insensitive to hydrologic changes when drinking water infrastructure and treatments function properly. Without treatment, precipitation in the spring/summer/fall and snowmelt in the winter/spring may flush a larger pollutant and pathogen load into drinking water systems and increase GI rates. A temporal lag between water contamination and seeking medical attention for GI is related to environmental transport, the disease system, and health-seeking behaviors. Environmental transport is influenced by hydrology, season of the year, and geographic context (urban vs rural). Depending on the hydrology and soil, precipitation events flush pathogens into groundwater over the course of a day to weeks. 18 The disease system includes variable pathogen incubation times, and virulence may produce clinical manifestations in hours to week(s) after infection. 19 Finally, health-seeking behaviors influence the lag between hydrologic events and cases. In urban Milwaukee, Wisconsin, families typically waited 2 days after experiencing symptoms to visit a clinic. 20 Living farther away from a health care facility and inclement weather may also delay seeking health care. 21,22 Most previous studies have focused on urban environments and few studies have examined how these factors relate in a more rural context. The study investigates if the type of drinking water source (treated municipal, untreated municipal, and private well water) modifies the effect of hydrology on childhood (aged < 5 years) GI health care visitations in Central and Northern Wisconsin. This study is a novel application of established geographic and temporal techniques to identify drinking water that may require better protection, treatment, or delivery.
