Environmental Drivers of Water Quality and Waterborne Disease in the Tropics with a Particular Focus on Northern Coastal Ecuador

Infectious diseases, especially waterborne diseases, are inextricably connected to environmental conditions. Not only is the transmission of the organisms that cause them mediated by their immediate environment, but larger scale ecological and social contexts often play a role in determining the incidence of these diseases in a community. Diarrheal illness remains one of the deadliest scourges on the planet, accounting for 2.5 million annual deaths of children worldwide. The body of research in this dissertation addresses the role of environmental drivers of water quality and waterborne disease in tropical countries, with a focus on the Borbon watershed in the northwestern Ecuadorian province of Esmeraldas. Chapter One concentrates on how best to assess microbial contamination in tropical waters, evaluating five techniques for measuring water quality based on their reliability, utility, and practicality for use in field situations. None of the indicators tested were ideal, and none exhibited a clear and consistent association with diarrheal disease incidence in the household. However, the three E.coli indicators performed better overall than the other indicator organisms. Chapter Two takes up the question of recontamination of water in households, describing the results of a controlled experiment to assess contamination of drinking water between the source and point-of-use. On average a more than half-log reduction of indicator organisms was observed between the source of drinking water and its point-of-use, followed by an average 0.2-log increase during storage. Chapter Three addresses sources of variability in water quality at varying timescales over the course of one year in one study village. The results suggest that a "runoff effect," influenced by peak rainfall events, operates at a seasonal timescale, whereas a "concentration effect," influenced by local contamination events, operates at a daily timescale in determining surface source water quality. For household water samples, both seasonality and household level factors affect variability in water quality. The theme of seasonality is carried into Chapter Four, which presents a systematic review and meta-analysis on the seasonal epidemiology of rotavirus in the tropics, concluding that rotavirus responds to changes in climate in the tropics, peaking at the colder and drier times of the year.