Characterizing the regional distribution and burden of cholera in Africa: Spatial modeling to guide prevention and control efforts
There are an estimated 2.8 million cholera cases per year globally, but the majority of these cases are not detected or reported. Because of inadequate surveillance and reporting the global distribution of cholera risk and its public health burden are poorly known. Fine resolution estimates of cholera burden and risk can serve as a crucial guide for efficient allocation of oral cholera vaccine. Previous attempts to determine the global burden of cholera have relied on a limited number of case studies that do not capture the broad range of settings and environmental conditions where cholera occurs. Here we assemble a massive database of highly detailed cholera incidence from a variety of government, scientific, and non-governmental agency sources, with a particular focus on sub-Saharan Africa where a majority of cholera cases have been reported in the past several decades but where the distribution of risk and burden is still poorly understood. We develop a hierarchical Bayesian modelling framework to estimate the cholera incidence and risk at a 5km scale across the entire African Continent. Our method allows us to synthesize environmental and socioeconomic variables with cholera incidence reports at different spatio-temporal scales, to estimate the cholera incidence with high spatial resolution.
Preliminary results for 10 countries in West Africa indicate an annual cholera incidence rate of 3.3 per 100,000 since 2009 with local incidence rates as high as nearly 8,000 per 100,000. Over four million people in these countries live in area with an annual incidence rate >100 per 100,000. The resulting maps can be used to identify areas of high or low incidence (and risk) at finer spatial scales than the country-level, such as at the province, district, or city-level. The identification of regions of high incidence or overall burden can be used to target vaccination and other control efforts. Work is ongoing to expand the model globally and incorporate additional explanatory variables. Improving our understanding of the spatial distribution of cholera and associating incidence with climate, environmental and socioeconomic factors will provide a basis for planning public health preventions to reduce cholera transmission.