Have We Substantially Underestimated the Impact of Improved Sanitation Coverage on Child Health? A Generalized Additive Model Panel Analysis of Global Data on Child Mortality and Malnutrition.

BACKGROUND: Although widely accepted as being one of the most important public health advances of the past hundred years, the contribution that improving sanitation coverage can make to child health is still unclear, especially since the publication of two large studies of sanitation in India which found no effect on child morbidity. We hypothesis that the value of sanitation does not come directly from use of improved sanitation but from improving community coverage. If this is so we further hypothesise that the relationship between sanitation coverage and child health will be non-linear and that most of any health improvement will accrue as sanitation becomes universal.

METHODS: We report a fixed effects panel analysis of country level data using Generalized Additive Models in R. Outcome variables were under 5 childhood mortality, neonatal mortality, under 5 childhood mortality from diarrhoea, proportion of children under 5 with stunting and with underweight. Predictor variables were % coverage by improved sanitation, improved water source, Gross Domestic Product per capita and Health Expenditure per capita. We also identified three studies reporting incidence of diarrhoea in children under five alongside gains in community coverage in improved sanitation.

FINDINGS: For each of the five outcome variables, sanitation coverage was independently associated with the outcome but this association was highly non-linear. Improving sanitation coverage was very strongly associated with under 5 years diarrhoea mortality, under 5years all-cause mortality, and all-cause neonatal mortality. There was a decline as sanitation coverage increased up to about 20% but then no further decline was seen until about 70% (60% for diarrhoea mortality and 80% for neonatal mortality, respectively). The association was less strong for stunting and underweight but a threshold about 50% coverage was also seen. Three large trials of sanitation on diarrhoea morbidity gave results that were similar to what would have been predicted by our model.

CONCLUSIONS: Improving sanitation coverage may be one of the more effective means to reduce childhood mortality, but only if high levels of community coverage are achieved. Studies of the impact of sanitation that focus on the individual's use of improved sanitation as the predictor variable rather than community coverage is likely to severely underestimate the impact of sanitation.