Elucidating pathways of fecal exposure : evidence from young children in rural Bangladesh

Causing nearly 0.5 million deaths in 2015, diarrhea is the second-leading cause of death among children between 1-59 months of age. Diarrhea is most often caused by pathogens transmitted through fecal-oral pathways: ingestion of fecally contaminated water, food, and soil or mouthing of contaminated hands and objects. Fecal contamination transmitted along these pathways, in combination with malnutrition, may also cause environmental enteropathy, a sub-clinical condition of the intestine. As with diarrhea, environmental enteropathy may result in malnutrition and stunting, which have long-term adverse effects on cognitive development and productivity in adulthood. Despite these concerns, the predominant pathway(s) of fecal matter transmission are poorly understood. Research into the relative contribution of each pathway to total ingestion of feces would help guide interventions to reduce fecal exposure. The research presented in this dissertation uses data on children's detailed interactions with the environment, combined with data on fecal contamination of various environmental reservoirs, to estimate the relative contribution of each pathway to children's total fecal ingestion. All four studies in this dissertation were carried out in the same rural communities in Bangladesh. In the first of two studies characterizing children's contacts with the environment, I conducted a structured observation of 149 children ages 3-18 months old. I detailed the frequency of children's hand-to-mouth and object-to-mouth contacts and recorded the prevalence and frequency of children's direct ingestion of soil and feces. I found that hand- and object-mouthing are frequent and higher than those documented for children in the U.S. These results suggest that, when assessing the environmental exposure faced by children in rural, low-income settings such as Bangladesh, the use of exposure data from children in the U.S. may underestimate risk. In the second study, I conducted video observations annually for three years to evaluate how children's environmental exposures change as they age. I captured the frequency, duration, and sequence of hand-to-mouth, object-to-mouth, and hand-to-object contacts of children 3-47 months old. Using the resulting longitudinal data in a random-effects model, I found that children's hand-to-mouth and object-to-mouth contact frequencies were associated with neither child age nor location of play, and that the mouthing frequencies of individual children are not correlated over time. In a third study, I combined the data from these observational studies with data on the amount of soil on hands and objects to model the quantity of soil ingested by children in rural Bangladesh. Estimated soil ingestion among children in rural Bangladesh was in the high end of the range of soil ingestion estimates for children living in high-income countries. The quantity of soil ingested was driven by direct ingestion of soil, mouthing of hands while not eating, and mouthing of objects. These results suggest that interventions to reduce fecal-oral disease should focus on preventing the direct ingestion of soil and improving children's hand hygiene. In the final study of this dissertation, I modeled the total ingestion of fecal matter by children in rural Bangladesh, including transmission through mouthing of hands and objects, as well as ingestion of food, water, soil, and feces. Children 6-23 months old ingest more fecal matter than children < 6 months or 24-35 months old; the direct ingestion of soil and mouthing of hands are the predominant pathways of fecal transmission. In this dissertation, I assess children's interactions with the environment at a detailed level and use this information in combination with environmental contamination levels to estimate children's ingestion of soil and fecal matter. In addition, I provide empirical evidence on the relative contribution of pathways that contribute to ingestion, which can help guide the design of interventions to reduce fecal-oral disease.

Advisor: Davis J. A. (Jennifer Ann)
Boehm Alexandria 
Leckie Jim
Luby Stephen