Epidemiological trends of reported syphilis incidence in Xihu district, Hangzhou, China, 2005-2025

Syphilis remains a critical global public health concern. The reported incidence of syphilis in Zhejiang Province has long stayed at a high level nationwide, with Xihu District of Hangzhou identified as a hyperendemic area for local syphilis transmission. This study used 2005-2025 surveillance data of Xihu District, Hangzhou to analyze syphilis trends for precise prevention evidence.

Syphilis surveillance data (2005-2025) for Xihu District were retrieved from China's National Notifiable Infectious Disease Reporting System. We calculated crude reported incidence rate for overall, primary, secondary, tertiary, and latent syphilis (per 100,000 population), and notification rate for congenital syphilis (per 100,000 live births). Joinpoint Regression 6.0.1 identified trend inflection points and computed period-specific annual percentage change (APC) and overall average annual percentage change (AAPC) across the 21-year span.

Total syphilis reported incidence rate presented an inverted U-shaped trajectory: rising rapidly from 68.71/100,000 in 2005 to the peak of 155.16/100,000 in 2010, followed by sustained sharp decline down to 13.17/100,000 in 2025, with the overall AAPC = -8.18% (p < 0.05). Four trends phases were identified: rapid growth (2005-2008, APC = 25.23%), mild decline (2008-2019, APC = -5.00%), accelerated decline (2019-2023, APC = -18.69%), and apparent reduction (2023-2025, APC = -39.01%). Latent syphilis dominated all stages throughout the study period. Primary and secondary syphilis shared long-term descending trends (AAPC = -14.76% and -12.19%, respectively). Tertiary syphilis remained at extremely low absolute levels with sparse case counts. Congenital syphilis surged in 2006-2007 and no notified congenital syphilis cases have been recorded since 2017. Gender disparity existed: females exhibited a faster overall descending rate (AAPC = -10.23%) than males (AAPC = -5.54%). The 20-39 age group consistently bore the highest reported incidence burden, with a long-term AAPC of -10.47%; the elderly (≥60 years) also showed prominent high reported incidence before 2019 and then dropped sharply (AAPC = -9.53%).

Syphilis control achieved substantial progress in Xihu District over two decades. Still, epidemiological challenges remain, including persistent vulnerability among young and older adults and hidden undiagnosed latent infections. Tailored interventions for high-risk groups, standardised latent-syphilis care, and sustained prevention of mother-to-child transmission are needed to lower residual disease burden.