Understanding the determinants of polio transmission and large-scale epidemiology remains a public health priority. In this study, we attempted to quantify the contribution of climate, environmental and demographic drivers related to sanitation, population growth and seasonality to the frequency and amplitude of polio outbreaks. Environmental and socioeconomic data were obtained from the World Bank and climate data were obtained from the Center for Environmental Data Analysis. We fitted a regression tree model to identify the main drivers of polio annual incidence data from the World Health Organization from 1980 to 2014 in 55 countries spanning 6 regions.
Results/Conclusions
While the precise ranking of predictors varied by geography and region, access to sanitation facilities was consistent across all regions, emphasizing the overall importance of this predictor for poliovirus transmission. As would be expected from epidemiological theory, another consistently significant predictor was vaccination coverage, with a strong association between polio incidence and the annual number of unvaccinated births. For more than 80% of countries, population density, and percent forest cover were also important predictors. Perhaps surprisingly, given polio is transmitted fecal-orally, climatic factors such as average temperature and total precipitation were ranked lowest among our predictors. One striking observation was the strong association at the global scale between country-specific per capita GDP and Wild poliovirus (WPV) incidence revealing a relationship between poverty and health. These analyses quantify the drivers of polio transmission dynamics in time and space and shed light on the global epidemiology of polio.