Shared Sanitation Facilities and Two Pathways of Diarrheal Disease Transmission: A Modeling Study

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In many low and lower-middle income countries, access to sanitation is limited for many individuals. Open defecation contaminates the environment and facilitates the transmission of diarrheal pathogens that are transmitted via the environment. The provision of sanitation facilities that are shared by many individuals, such as shared latrines in slums, are considered by many public health officials as the only short-term solution to this problem, especially in urban slums in Asia and Africa. However, epidemiological evidences have shown that shared sanitation may actually increase the prevalence of diarrheal diseases. One hypothesis that may explain this phenomenon is that many different pathogens may cause diarrhea. While sanitation facilities reduce the contamination of the environment by human defecation, unhygienic sanitation facilities are actually fomites for the transmission of other diarrheal pathogens that are transmitted directly between humans. We propose a mathematical model that seeks to explain how the alleviation of environmental transmission of pathogens such as cholera via shared sanitation can lead to an amplification of direct transmission caused by other diarrheal diseases such as norovirus. The model is an ordinary differential equation (ODE) model that runs parameters chosen from a Latin hypercube sampling. After sieving through the parameter space to select parameter sets yielding outbreaks within a specified threshold, varying levels of shared sanitation coverage are implemented on these sets. Changes in disease prevalence are then plotted with respect to these varying levels of shared sanitation intervention. Results give quantifiable evidence that in the presence of an environmental and a person-to-person spread pathogen, total disease prevalence can increase. Under certain conditions the model shows an optimal level of shared sanitation intervention that can decrease environmental disease prevalence while not increasing person-to-person transmission too much. In any case, shared sanitation is most effective when viewed as a long term strategy.


American Society of Tropical Medicine and Hygiene Annual Meeting (ASTMH)


Atlanta, GA