This study has some limitations. First, HFMD is caused by several enteroviruses.In this study,there was no detailed information on causal agents, for example, EV71 or CVA16 are responsible for the outbreaks among islands during the study period.This may affect the disease duration or peak of outbreaks.Second,the transmission chain of HFMD among areas defined in this study was not taken in to consideration. This also impacts the spread of HFMD between or within the study areas. Finally, the studied period was too short to make strong conclusions, and extended data are needed for validating the association found in this study.