Evaluating Objective Biological Measures to Characterize Enteropathogen Exposure

Abstract

The need for new metrics for the accurate assessment of Water, Sanitation, and Hygiene (WASH) interventions has been highlighted by the recent unexpected results from large-scale, cluster randomized intervention trials. Several reasons have been postulated about what may have caused these largely null results. In this dissertation, my primary focus is on the fact that these trials relied on exposure variables that measured the indirect impact of WASH interventions on pathogen loads and exposure and outcome variables based on self-report. A move towards exposure and outcome variables that are more specific may provide new insights into developing more targeted interventions. My secondary focus is on urban WASH, which has been understudied given that most WASH studies have been conducted in rural areas. Urban WASH is important because by 2050 68% of the world’s population will reside in urban areas, often in informal settlements. These high-density informal settlements will present unique environmental risk factors. New metrics based on biological measures, such as pathogen quantification and assessments of physiological and immunological states will be necessary to inform the design of sustainable and effective interventions for urban areas. In this dissertation, I present three research aims focusing on improving our understanding of WASH in urban areas using biological measures. Aim 1, examined the association between pathogen carriage in infants and biomarker derived scores. We used seven stool biomarkers to derive scores that measure gut integrity, acute inflammation, and chronic inflammation. The use of these biomarkers provides a novel way to gain insight on specific pathogenic processes when coupled with pathogen data. Score-pathogen relationships were found to be enteropathogen-specific, reflecting expected physiological processes of epithelial invasion and gut dysfunction. Even though the biomarkers can be accurate measures of cellular damage and allow the evaluation of specific components of the inflammatory process, relationships between biomarkers are complex and depend on their cellular origin and the level of measurement. We postulate that there are multiple cellular damage processes that may differ between individuals and populations that have an end-state characterized by a run-away immune response, gut damage, and chronic malaise. In Aim 2, we conducted a survey in urban informal settlements in Addis Ababa, Ethiopia to understand WASH indicators associated diarrheal prevalence in infants. We found that diarrheal prevalence was strongly associated with water treatment regime, and that boiling and water filtration were the most effective disease barriers. Our findings suggest that utility water in Addis Ababa is a major disease conduit and that systemic improvements are necessary to make utility water safe. In Aim 3, we conducted a cross-sectional study, collecting and testing soil and water samples for a range of pathogens from urban and rural sites in and around Yangon, Myanmar. We quantified the concentrations of a range of viral, bacterial, and protozoan pathogens and one fecal indicator. We found that pathogen counts in both water and soil were significantly higher in urban areas compared to rural areas. We also found pathogen specific associations between environmental risks and environmental pathogen loads. Indicator and bacterial environmental loads were found to be associated with environmental risks, while environmental viral loads were not associated with any observed environmental risks. Our work highlights how environmental pathogen measurements provide added specificity towards identifying important environmental pathways that require mitigation; and measuring pathogens provides additional specificity than measuring indicator organisms.