Estimation of abrupt changes in sentinel observation data of influenza epidemics in Japan

Sentinel observations of influenza epidemic in each prefecture indicates basically unimodal trend but with irregular shocks, which are synchronous among prefectures. In this study, we have examined the possibility that the observed treads can be modeled by SIR with stochastic outer force added. The result shows that this is formally possible but large outer forces are needed in some prefecture.