Risk Assessment of Dengue Autochthonous Infections in Tokyo during Summer, Especially in the Period of the 2020 Olympic Games.

An outbreak of autochthonous dengue fever occurred in the summer of 2014 in Tokyo, Japan. Numerous participants and spectators from abroad are expected to visit Tokyo in the summer of 2020. This study aims to analyze the risk of autochthonous dengue infections in Tokyo in summer and also assess the additional risk in the Olympiad using a mathematical model. A stochastic transmission model was developed with the cooperation of seasonal factors that greatly influence the transmission cycle of dengue virus, and stochastic simulations were conducted for each scenario provided adequately. This study found that (i) the incidence of dengue autochthonous infections is predicted to occur in a small number of cases; (ii) the local climate greatly influences the scale of dengue autochthonous infections; (iii) the incidence reaches its peak in August and early September; and (iv) the possibility of progressing to dengue outbreak is rare. In the Olympiad to be held in the summer of 2020, an additional risk of dengue autochthonous infections will amount to double compared with that in other years.