Childhood exposure to enteric pathogens from hands and drinking water in Tanzania [electronic resource]

In 2012, 6.6 million children died before reaching their fifth birthday. One in every ten of these deaths was the result of diarrheal disease, which causes some 1,800 under-5 deaths each day. Low-income countries bear a majority of the morbidity and mortality burden from childhood diarrhea, and the highest rates child diarrhea cases occur in sub-Saharan Africa. Transmission of diarrhea-causing pathogens occurs through several exposure routes including drinking water and hands, but the relative importance of each route is not well understood. Without knowing the relative contribution, it is challenging for policy makers and low-income country governments to efficaciously prioritize funding for water and hygiene based interventions. Using the sub-Saharan African town of Bagamoyo, Tanzania, as a case study, this dissertation aims to evaluate the relative contribution by characterizing the prevalence and drivers of childhood exposure to enteric pathogens and human feces by contaminated hands and stored water. The first research chapter of this dissertation (Chapter 2) examines the prevalence of enteric pathogens on mothers' hands, in community water sources, and in water stored in Tanzanian homes. In each sample type, the presence of molecular markers for three enteric viruses (enterovirus, adenovirus, and rotavirus), seven Escherichia coli virulence genes (ECVG), and human-specific Bacteroidales was assessed. Culture-based fecal indicator bacteria (FIB) (E. coli and enterococci) and turbidity of water and hand rinses were also measured. The relationship between water and hand pathogen contamination, as well as the association between different water source or sanitation infrastructure and pathogen contamination, was examined. Finally, the ability of FIB and turbidity to serve as predictors of pathogen contamination in water and on hand was assessed. The occurrence of ECVG was equivalent across all sample types. ECVG were more likely to be found in unimproved water sources, but both ECVG and viral genes were detected in improved water sources. ECVG were more likely found in stored water of households with unimproved sanitation facilities. FIB and turbidity were good predictors of ECVG presence, whereas turbidity and human-specific Bacteroidales were good predictors of viruses. The results provide insights into the distribution of pathogens in Tanzanian households and offer evidence that both hand washing and improved water management practices could alleviate viral and bacterial diarrhea. Hands as vectors of enteric viruses are investigated further in Chapter 3 by evaluating norovirus contamination on hands of Tanzanian mothers during the rainy and dry seasons. Norovirus was chosen because it is the most common cause of viral gastroenteritis worldwide and one of the leading causes of viral diarrhea in children under age five. Norovirus GII was detected in approximately five percent of hand rinse samples during both the rainy and dry seasons, suggesting that mothers' hands serve as a source of norovirus exposure for young children in Tanzanian households. Levels of FIB (E. coli and enterococci) were not associated with norovirus hand contamination. Turbidity was found to be associated with norovirus presence on mother's hands; however, this relationship was only observed during the rainy season. Further research is needed to determine consistent indicators for norovirus contamination. In particular, future work should evaluate whether human-specific Bacteroidales may serve as a more consistent indicator for norovirus presence on hands in Tanzania. Chapter 4 builds on the characterization of enteric pathogen exposure from water and hands in Chapter 2 by exploring the association between pathogen contamination and the presence of a sick child in the home. The overall prevalence of enteric pathogen genes and the Bacteroidales human specific fecal marker found in stored water and on hands suggests extensive environmental contamination within homes both with and without reported child diarrhea. However, better stored water quality was found among households with diarrhea, suggesting that caregivers with sick children may be more likely take steps to improve water quality of stored water in the home. In order to further evaluate this conclusion, Chapter 4 also examines the association between enteric pathogen contamination and water management and hygiene behaviors. Mothers who had recently contacted food or water were more likely to have detectable levels of ECVG or human feces on their hands; while mothers who used reportedly less water for hand washing were less likely to have enteric viruses (rotavirus, enterovirus, or adenovirus) on their hands. Enteric virus and human fecal molecular markers were more likely found in the stored drinking water of households in which the markers were also detected on hands. Stored water collected from an improved source was less likely to have ECVG or human fecal contamination, and households using improved sanitation facilities were less likely to have ECVG contaminated stored water. Together the results of the water and hygiene behavior models suggest that interventions to increase the quantity of water available for hand washing, and to improve food hygiene, may reduce exposure to enteric pathogens in the domestic environment. In addition, use of improved water sources and sanitation facilities may help to reduce contamination of household stored drinking water. The final research chapter of the dissertation (Chapter 5) examines the relative contribution of hands and water to a Tanzanian child's daily fecal exposure using water and hand FIB data and a stochastic modeling approach. The results of the model show that Tanzanian children under the age of five ingest a significantly greater amount of human feces each day from hand-to-mouth contacts than from drinking household stored water. These results can help explain why interventions focused on water without also addressing hygiene often yield little or no effect on reported incidence of diarrhea in some settings. By simulating exposure separately for each United States Environmental Protection Agency (EPA) age risk category under the age of five, the model is able to show that hands, compared to water, are particularly important for children in their first six months of life. Therefore, interrupting the transmission of enteric pathogens from hands for this age group may have long-term growth and cognitive benefits. Overall, the model framework can aid policy makers and governments in the allocation of WASH funding for the reduction of childhood diarrhea by allowing them to evaluate the relative contribution of fecal exposure pathways within sub-Saharan African homes. The research in this dissertation combines tools from microbiology, engineering, and epidemiology to characterize pathogen exposure to children by contaminated hands and stored drinking water in a low-income country. This dissertation provides insights into the sources of a child's exposure to diarrhea-causing pathogens in the household environment and can inform debates about efficacious ways to reduce the burden of childhood diarrheal disease in low-income countries. Specifically, the results of this work highlight the important role that hands play in the exposure of young children to diarrhea-causing pathogens. As such, hygiene education and promotion, as well as providing enough water for proper hand hygiene, should be a priority for policy makers. In addition, the results of this work demonstrate the need for investments in improved sanitation infrastructure to reduce the high levels of fecal contamination in the environments of young children living in low-income countries.

Keywords: Civil and Environmental Engineering.
Advisor: Boehm Alexandria primary advisor. Thesis advisor
Davis J. A. (Jennifer Ann)
Luby Stephen advisor. Thesis advisor
Mitch William A. advisor. Thesis advisor