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The Epidemiology of Cholera in Zanzibar: Implications for the Zanzibar Comprehensive Cholera Elimination Plan
Qifang Bi | Fadhil M Abdalla | Salma Masauni | Rita Reyburn | Marko Msambazi | Carole Deglise | Lorenz von Seidlein | Jacqueline Deen | Mohamed Saleh Jiddawi | David Olson | Iriya Nemes | Jamala Adam Taib | Justin Lessler | Ghirmay Redae Andemichael | Andrew S Azman
Date of Publication:
The Journal of Infectious Diseases
Cholera poses a public health and economic threat to Zanzibar. Detailed epidemiologic analyses are needed to inform a multisectoral cholera elimination plan currently under development. 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. Using flexible regression models, we estimated cholera’s seasonality and the relationship between rainfall and cholera transmission.
From 1997 and 2017, 11921 suspected cholera cases were reported across 87% of Zanzibar’s shehias, representing an average incidence rate of 4.4 per 10,000/year. The geographic distribution of cases across outbreaks was variable, although a number of high-burden areas were identified. Outbreaks were highly seasonal with two high-risk periods corresponding to the annual rainy seasons.
In conclusion, shehia-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.
The Case for Reactive Mass Oral Cholera Vaccinations
Rita Reyburn | Jacqueline L. Deen | Rebecca F. Grais | Sujit K. Bhattacharya | Dipika Sur | Anna L. Lopez | Mohamed S. Jiddawi | John D. Clemens | Lorenz von Seidlein | Edward T. Ryan
Date of Publication:
PLoS Neglected Tropical Diseases
Cholera outbreaks have had catastrophic impact on societies for centuries. Despite more than half a century of advocacy for safe water, sanitation and hygiene, approximately 100,000 cholera cases and 5,000 deaths were reported in Zimbabwe between August 2008 and by July 2009. Safe and effective oral cholera vaccines have been licensed and used by affluent tourists for more than a decade to prevent cholera. We asked whether oral cholera vaccines could be used to protect high risk populations at a time of cholera. We calculated how many cholera cases could have been prevented if mass cholera vaccinations would have been implemented in reaction to past cholera outbreaks. We estimate that determined, well organized mass vaccination campaigns could have prevented 34,900 (40%) cholera cases and 1,695 deaths (40%) in Zimbabwe. In the sites with endemic cholera, Kolkata and Zanzibar, a significant number of cases could have been prevented but the impact would have been less dramatic. The barriers which currently prevent the implementation of mass vaccinations, including but not only the cost to purchase the vaccine, seem insurmountable. A concerted effort of donors and key decision makers will be needed to offer better protection to populations at risk.