Abstract: 【Abstract】 Objective To investigate the epidemic trends of syphilis in Sichuan province from 2005 to 2024, and to provide a scientific basis for formulating prevention and control strategies. Methods A descriptive study was conducted. The epidemic data on syphilis in Sichuan province from 2005 to 2024 were obtained from the Infectious Disease Surveillance System of China Information System for Disease Control and Prevention. The Joinpoint regression model was used to analyze incidence trends, and the annual percent change （APC） and average annual percent change （AAPC） of syphilis incidence were calculated. The age-period-cohort model was applied to investigate the effects of ages, periods and birth cohorts on syphilis incidence. Results Joinpoint regression analysis showed that the reported incidence rate of syphilis in Sichuan province increased from 4.72 per 100 000 in 2005 to 67.15 per 100 000 in 2024 （AAPC = 15.56%, P < 0.001）; the APC was 40.54% （P = 0.003） from 2005 to 2010, 5.65% （P > 0.05） from 2010 to 2022, and 21.33% （P < 0.001） from 2022 to 2024. The incidence rate of primary and secondary syphilis showed an initial increase followed by a decrease, with 2010 as the turning point; the incidence rate of tertiary syphilis successively evolved through rapid increase, slowed growth, and relatively stable phases, with inflection points in 2009 and 2020; the incidence rate of congenital syphilis showed an initial increase followed by stability and then a decline, with turning points in 2009 and 2012; the incidence rate of latent syphilis demonstrated a rapid increase followed by a slowdown in growth, with 2010 as the turning point. The AAPC of the reported incidence was 14.97% in males and 16.15% in females （both P < 0.001）. The AAPCs were -3.96% （P = 0.023）, 18.40% （P < 0.001）, 13.01% （P < 0.001）, and 19.74% （P < 0.001） in the age groups of < 10, 10 - 19, 20 - 49, and ≥ 50 years, respectively. The age-period-cohort model indicated that the longitudinal age curve of syphilis incidence showed a J-shaped upward trend, peaking in the age group of 80 - 84 years; with the 2010 - 2014 period as the reference group, the period effect on the risk of syphilis showed an upward trend; with the 1970 - 1974 birth cohort as the reference group, the cohort effect on the risk of syphilis peaked in the 2010 - 2014 birth cohort, showing an initial increase followed by a decrease. Conclusions The reported incidence rates of primary and secondary syphilis, and congenital syphilis in Sichuan province showed a downward trend in 2010 and 2012, respectively. However, the overall reported incidence of syphilis exhibited an upward trend from 2005 to 2024. The reported incidence of syphilis was influenced by ages, periods, and birth cohorts.

Key words: Syphilis, Sichuan, Incidence, Trend analysis, Joinpoint regression model, Age-period-cohort model