7.1 Conclusions
The major conclusions from the papers included in this dissertation are listed below: 1). GIS and spatial statistics were applied to examine whether diarrheal diseases were clustered in space and time. All three types of diarrheal diseases were clustered either in space or space and time.
2). Tubewell density was inversely associated with childhood diarrheal diseases, namely, children are less likely to contract diarrhea if there are more tubewells around the bari where they live. In addition, intermediate depth wells were associated with a higher risk of childhood diarrhea than shallow wells and deep wells.
3). There was an increase in the likelihood of childhood diarrhea for children drinking from shallow wells with higher arsenic compared to wells with lower arsenic after adjusting for flood control, population density and SES. This suggests that the health benefits of reducing As exposure by switching from a shallow high-As tubewell to a shallow low-As are to some extent countered by an increase in childhood diarrhea risk. 4). The virus concentration method developed in this study is simple and cost-effective, and can be used efficiently to recover adenovirus 41 from turbid water samples. In addition, this is the first application of sample evaporation to concentrate viruses in water samples.
5). Hollow fiber ultrafiltration is an effective technique for recovering and concentrating multiple classes of microorganisms rapidly and simultaneously. However, the recovery efficiencies varied among the different microbes and different water matrices.
In summary, the main part of this dissertation involved the analysis of 60,000 cases of diarrheal disease in children under five in a population drinking primarily untreated groundwater. To my knowledge, this is the first epidemiological study focused on the relationship between childhood diarrhea, tubewell access and depth, and As levels in groundwater. The main finding shows that children under five drinking water from shallow wells that are low in arsenic are in fact more likely to have diarrheal disease. This information is important for relevant policy-makers to make appropriate strategies for waterborne diarrhea disease reduction and arsenic mitigation.
7.2 Future research
In these studies, risk factors for childhood diarrhea were examined. However, it is unknown what factors are related to diarrheal diseases caused by specific pathogens. Given the availability of data, exploring the relationship between diarrhea caused by Shigella and rotavirus and these risk factors related to water and other exposure routes is an important next step.
It is surprising to find that intermediate depth wells are associated with a higher risk of diarrhea compared to shallow wells. This finding merits further research. It would be interesting to evaluate whether intermediate depth wells are more vulnerable to fecal contamination. Also, mechanisms for pathogen transport into the drinking water from intermediate depth wells need to be investigated.
pathogens in tubewell water. E. coli in tubewell water has been monitored each month since 2008 (van Geen et al., 2011) and childhood diarrhea cases are continuously collected by ICDDR, B CHWs. Given the availability of E. coli and childhood diarrhea data, future research should statistically evaluate whether there is an association between the concentration of E. coli or of other enteric microbes in groundwater and cases of diarrhea among children who drink that water in space and time.
A novel method was developed to concentrate adenovirus 41 in small volumes of source water. Additional research is needed to evaluate the efficacy of this method for concentrating other types of enteric viruses. Performance of the method in field application also needs to be demonstrated, especially in water for which there is evidence of fecal contamination and waterborne diarrheal disease risk.
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