Abstract
BACKGROUND: In recent years, a notable increase in syphilis cases has been observed in Japan, aligning with global trends. We aimed to elucidate the trends in sexually transmitted infections (STIs) incidence (specifically syphilis) in Japan and examine its relationship with the number of sex industry-related businesses in prefectures. METHODS: Data on STIs and the number of sex industry-related businesses from 2000 to 2022 were obtained from the National Institute of Infectious Diseases (NIID) and the official website of the Japan National Crime Prevention Association, respectively. Joinpoint analysis and regression analysis were used to identify inflection points in the trend of syphilis and describe the association between STI incidence and the overall number (and the number of different categories) of sex industry-related businesses (i.e., store-based soaplands, store-based fashion health, nude studio, love hotels, adult shops, and meeting cafes, and non-store-based including dispatch-type fashion health and adult video mail orders). The population data was obtained from the 2022 population estimates provided by the Statistics Bureau of the Ministry of Internal Affairs and Communications. RESULTS: In this study, a significant increase in the number of syphilis cases has been observed in Japan in recent years, with joinpoint analysis identifying a significant inflection point in 2020 (annual percent change: 43.8). Multiple regression analysis adjusted for the prefectural population revealed a strong association between the incidence of STIs and number of sex industry-related businesses. Specifically, a strong association was observed between the number of Category I non-store-based sex-related business syphilis cases among men (standardized β=0.908, p<0.001, R(2)=0.938) and women (standardized β=1.017, p<0.001, R(2)=0.921), as well as AIDS cases for men (standardized β=0.991, p<0.001, R(2)=0.910). CONCLUSIONS: The significant increase in syphilis cases in Japan among men and women may be related to an increase in non-store-based, dispatch-type fashion health sex-related businesses. These findings indicate that public health policies should consider these specific social and behavioral factors in future interventions.