摘要：Objectives. We investigated whether deep tube wells installed to provide arsenic-free groundwater in rural Bangladesh have the added benefit of reducing childhood diarrheal disease incidence. Methods. We recorded cases of diarrhea in children younger than 5 years in 142 villages of Matlab, Bangladesh, during monthly community health surveys in 2005 and 2006. We surveyed the location and depth of 12 018 tube wells and integrated these data with diarrhea data and other data in a geographic information system. We fit a longitudinal logistic regression model to measure the relationship between childhood diarrhea and deep tube well use. We controlled for maternal education, family wealth, year, and distance to a deep tube well. Results. Household clusters assumed to be using deep tube wells were 48.7% (95% confidence interval = 27.8%, 63.5%) less likely to have a case of childhood diarrhea than were other household clusters. Conclusions. Increased access to deep tube wells may provide dual benefits to vulnerable populations in Matlab, Bangladesh, by reducing the risk of childhood diarrheal disease and decreasing exposure to naturally occurring arsenic in groundwater. Diarrheal disease remains the second largest cause of death for children worldwide, making it a major threat to child health. 1 Research from a 6-village study area in Bangladesh suggests that deep tube wells may help reduce this disease burden because they access the deep aquifer, which has lower levels of arsenic and may have lower levels of fecal contamination. 2 We have expanded on this work by looking at the effect of deep tube well use across a broader study area and by considering whether distance to a deep tube well plays a role in childhood diarrheal disease risk among deep tube well users. During the 1970s and 1980s, rural Bangladeshis made a nearly universal shift from drinking surface water to drinking ground water. The efforts of the United Nations International Children’s Emergency Fund, the Bangladesh Department of Public Health and Engineering, and nongovernmental organizations led to the installation of millions of tube wells throughout the country. 3 Most of these tube wells tap into the shallow aquifer (< 140 ft) and provide drinking water that is generally considered safe. Tube wells are installed with a hand percussion drilling method that drives polyvinyl chloride pipe to the aquifer; thus installation is inexpensive and feasible for even relatively poor households. The Bangladeshi government and the international community’s campaign in the 1970s and 1980s to promote the use of groundwater for drinking was effective: the majority of rural residents were drinking tube well water by the early 1990s. Coupled with general improvements in hygiene and sanitation, the shift from drinking surface water to drinking groundwater is suggested to have influenced the decline in diarrhea-induced deaths observed in Bangladesh. 4 Although the proliferation of tube wells addressed problems associated with drinking contaminated surface water, it exposed individuals to a new health risk. Naturally occurring arsenic levels exceeding the World Health Organization’s and the government of Bangladesh’s drinking water standards (10 μg/L and 50 μg/L, respectively) were identified in the 1990s. An estimated one half of the country’s population was exposed to levels exceeding the World Health Organization standard, and nearly one third was drinking water exceeding the Bangladesh standard. 5 By 2000, an article in the Bulletin of the World Health Organization had declared a “public health emergency,” noting studies that an estimated 1 in 10 people with prolonged exposure to drinking water containing 500 micrograms per liter of arsenic will eventually die of cancer. 6 Even at lower doses, long-term exposure to arsenic-contaminated drinking water can lead to health problems ranging from skin problems to cancer. 7,8 In response to these developments, nearly 5 million wells were tested for arsenic under the Bangladesh Arsenic Mitigation and Water Supply Program. Tube wells exceeding the Bangladesh arsenic standard were painted red, whereas safe wells were painted green. This was intended to provide residents with information about the relative danger or safety of tube well water supplies and to allow informed behavioral change. Bangladeshis’ primary mitigation response was to switch from a shallow high-arsenic well to the nearest shallow low-arsenic well. However, it has been suggested that local hydrogeology and poor sanitation have led to higher levels of fecal contamination in shallow low-arsenic wells, 9 leading to concern that residents who switch from shallow high-arsenic wells to shallow low-arsenic wells may face higher diarrheal disease risk. 10 In fact, an increase in diarrhea was recently shown among rural households using shallow low-arsenic wells. 11 Exposure to either high-arsenic concentrations or high fecal contaminants in shallow wells indicates a need for alternative drinking water sources. After switching to a low-arsenic shallow well, the second most common arsenic mitigation strategy is to obtain drinking water from a deep tube well tapping into an aquifer that is usually more than 500 feet deep. Since 2000, an estimated 165 000 deep tube wells have been installed throughout Bangladesh. Most deep tube wells are public and are installed with aid from the Bangladesh Arsenic Mitigation and Water Supply Program, the Department of Public Health and Engineering, and nongovernmental organizations. 12,13 Private ownership of deep tube wells is rare because of high installation costs. Public deep tube wells are, therefore, often located near a rural road or walking path where villagers will have easy access. Use of a deep tube well may increase walking distance for water collection, given their location in public areas rather than near households. Prior research indicates that villagers may be willing to walk only up to 150 meters to obtain drinking water. 14 Additionally, it is possible that longer distances to a deep tube well increase the chances of fecal contamination of stored water supplies, as people who walk farther for water may collect more water at any given time and store it for longer to minimize trips to the well. Any risk of contamination during storage, however, may be balanced by the decreased likelihood of contamination during water extraction from a deep tube well. Such a protective association between deep tube well use and childhood diarrhea incidence has been identified in a study in 6 villages in rural Bangladesh, 2 but the sample was small in that study. We built on those findings by measuring the relationship between deep tube well use and childhood diarrheal disease in an expanded study area. We also investigated the role played by distance to a deep tube well.
