Intra-area factors dominate the spatio-temporal transmission heterogeneity of hand, foot, and mouth disease in China: A modelling study

Hand, foot, and mouth disease (HFMD) has been a serious threat to children's health in China since 2008, and quantifying the transmission heterogeneity of HFMD is crucial for understanding its spatio-temporal dynamic mechanisms and developing precise disease containment strategies. In this study, surveillance data of HFMD cases for patients 15 years of age or younger in east Mainland China between 2009 and 2015 was retrieved from the national surveillance system, and then an age and gender–stratified spatiotemporal Bayesian hierarchical model was built with three types of transmission hazards (intra-area transmission, inter-area transmission, and environmental risk factors). Spatial and temporal heterogeneities of HFMD transmission were quantified by the contribution of the hazard components over time and regions. In addition, the transmission heterogeneity by age–gender subgroups was determined by the transmission probabilities derived from the transmission rate matrix. We found that the intra-area transmission hazard dominated HFMD transmission (56.4% to 96.3%), followed by environmental risk factors (1.1% to 42.1%), whereas the contribution of the inter-area transmission hazard component was relatively small (1.5% to 3.6%). During school holidays, the contribution of the inter-area transmission component caused an instantaneous increase in the overall transmission hazard. In addition, the cumulative hazard contribution across time varied with the geographic region, and three distinct clusters were identified and related with the size of the local population. Moreover, the transmission probability was the highest among the same age–gender group within the intra-area transmission hazard, whereas inter-area and environmental transmission hazards had stronger effects among older children. HFMD transmission varied significantly over time, geographical regions, and age–gender subgroups. Development of targeted and individualized precise policies of HFMD control can benefit from illuminating its spatiotemporal transmission heterogeneity and consideration of the characteristics of population at risk.