Abstract
Poor sanitation could pose greater risk for enteric pathogen transmission at higher human population densities because of greater potential for pathogens to infect new hosts through environmentally mediated and person-to-person transmission. We hypothesized that incidence and prevalence of diarrhea, enteric protozoans, and soil-transmitted helminth infections would be higher in high-population-density areas compared with low-population-density areas, and that poor sanitation would pose greater risk for these enteric infections at high density compared with low density. We tested our hypotheses using 6 years of clinic-based diarrhea surveillance (2007–2013) including 4,360 geolocated diarrhea cases tested for 13 pathogens and a 2010 cross-sectional survey that measured environmental exposures from 204 households (920 people) and tested 701 stool specimens for enteric parasites. We found that population density was not a key determinant of enteric infection nor a strong effect modifier of risk posed by poor household sanitation in this setting.
Highlights
Most enteric pathogens are spread by fecal–oral transmission that is facilitated by the close contact of people either through direct, person-to-person transmission or through indirect, environmentally mediated transmission.[1]
Improved sanitation conditions have been generally associated with reduced diarrhea[7] and soil-transmitted helminth (STH) infections,[8] but three recent sanitation intervention studies in rural India found no reductions in diarrhea or STH infections despite large improvements in latrine coverage9–11—one of which found no evidence for effect modification of sanitation improvements by local population density.[11]
A limitation of the sanitation intervention studies was imperfect compliance, which could have underestimated the benefits of universal sanitation, but heterogeneity in the risk posed by poor sanitation has been predicted by theory due to the complexity of enteric pathogen transmission and the importance of environmental context to transmission.[1,12]
Summary
Most enteric pathogens are spread by fecal–oral transmission that is facilitated by the close contact of people either through direct, person-to-person transmission or through indirect, environmentally mediated transmission.[1]. Population density may be one important source of heterogeneity, and if so, enteric infection studies designed explicitly around questions of population density and its relationship to poor sanitation will help guide future intervention programs. We are aware of few empirical studies of the relationship between population density and enteric infection risk.[13,14,15] Most studies have found higher enteric infection risk at higher popu-
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