日本性感染症学会誌 Journal of Japanese Society for Sexually Transmitted Infections

In this study, we analyzed the reports of syphilis cases in the National Epidemiological Surveillance of Infectious Diseases to describe the current nationwide syphilis outbreak in Japan. The number of primary and secondary syphilis cases had increased since 2011, reaching 7,003 cases in 2018 (4,589 male and 2,414 female). In 2018, males aged 40–44 years gained the highest syphilis notification rate among all age groups, and the increase was most noticeable among those aged 20–39 years. Meanwhile, females aged 20–24 years gained the highest syphilis notification rate and the highest increase. Heterosexual contacts accounted for approximately 70% of the male cases and nearly all female cases who reported their transmission routes. The overall increasing trend of notification for heterosexual and homosexual contacts in both males and females remained the same. Furthermore, the heterosexual transmission reports among males in Tokyo, which accounted for nearly 20% of syphilis cases nationwide, gradually decreased in the past several months. While careful monitoring of this changing trend is necessary, it is critical to promote education on avoiding casual sex and the importance of protected sex to adolescents, early diagnosis and proper treatment by healthcare workers, and contact investigation in case of clustering among high-risk population to control the current syphilis outbreak. Communication among stakeholders and citizens is also a key to control such outbreak, and the new reporting format of the national syphilis surveillance, which started in 2019, with additional information on pregnancy may play an important role in this health issue.