Introduction Syphilis incidence has increased sharply in high-income countries since 2012, including Japan. Nagasaki Prefecture has not previously been subject to detailed epidemiological analysis of syphilis. This study aimed to characterize the epidemiological trends, demographic characteristics, and spatiotemporal distribution of syphilis in Nagasaki Prefecture from 2014 to 2023. Methods A descriptive epidemiological study was conducted using 10-year infectious disease surveillance data from Nagasaki Prefecture. Cases were analyzed by time, person, and place distribution. Joinpoint regression analysis was performed to identify significant changes in incidence trends and calculate the annual percentage change (APC). Compound annual growth rates (CAGR) were calculated for overall and stage-specific incidence. Results A total of 423 syphilis cases were reported, with the overall incidence rate increasing from 1.26 per 100,000 in 2014 to 11.81 per 100,000 in 2023, representing a 9.4-fold increase with a CAGR of 28.1%. Joinpoint regression identified 2021 as a significant inflection point, with the APC accelerating from 11.83% during 2014–2021 to 99.69% during 2021–2023. Young adults aged 18-34 years showed the most pronounced increase (from seven cases in 2014 to 75 cases in 2023, a 10.7-fold increase). Among cases with documented exposure history, 42.1% (82/195) reported sex industry involvement. Cases were geographically concentrated in Nagasaki City, Sasebo, Isahaya, and Omura. Conclusion These findings highlight the disproportionate burden among young adults and the substantial role of sex industry exposure. Targeted screening, integrated HIV-syphilis testing, and strengthened urban surveillance should be prioritized.
Tu et al. (Tue,) studied this question.