Abstract
BackgroundCholera poses a public health and economic threat to Zanzibar. Detailed epidemiologic analyses are needed to inform a multisectoral cholera elimination plan currently under development.MethodsWe collated passive surveillance data from 1997 to 2017 and calculated the outbreak-specific and cumulative incidence of suspected cholera per shehia (neighborhood). We explored the variability in shehia-specific relative cholera risk and explored the predictive power of targeting intervention at shehias based on historical incidence. Using flexible regression models, we estimated cholera’s seasonality and the relationship between rainfall and cholera transmission.ResultsFrom 1997 and 2017, 11921 suspected cholera cases were reported across 87% of Zanzibar’s shehias, representing an average incidence rate of 4.4 per 10000/year. The geographic distribution of cases across outbreaks was variable, although a number of high-burden areas were identified. Outbreaks were highly seasonal with 2 high-risk periods corresponding to the annual rainy seasons.ConclusionsShehia-targeted interventions should be complemented with island-wide cholera prevention activities given the spatial variability in cholera risk from outbreak to outbreak. In-depth risk factor analyses should be conducted in the high-burden shehias. The seasonal nature of cholera provides annual windows of opportunity for cholera preparedness activities.
Highlights
Cholera poses a public health and economic threat to Zanzibar
We explored the variability in shehia-specific relative cholera risk and explored the predictive power of targeting intervention at shehias based on historical incidence
Shehia-targeted interventions should be complemented with island-wide cholera prevention activities given the spatial variability in cholera risk from outbreak to outbreak
Summary
We collated passive surveillance data from 1997 to 2017 and calculated the outbreak-specific and cumulative incidence of suspected cholera per shehia (neighborhood). We explored the variability in shehia-specific relative cholera risk and explored the predictive power of targeting intervention at shehias based on historical incidence. Zanzibar consists of 2 main islands, Unguja (2012-population 896 721) and Pemba (2012-population 406 846), 40 and 60 km from mainland Tanzania. Unguja is home to the majority of tourism, the government offices, and the main ports for trade. Based on the 2015–2016 Demographic Health Survey (DHS), almost all households (98%) in Zanzibar obtain their drinking water from improved sources [3]. 55% of households had a dedicated place for washing hands, and 14% of households reported spending 30 minutes or longer (round trip) to fetch drinking water
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