Thirty-Year trend of Syphilis during the periods of the resurgence, HIV risk compensation and COVID-19 pandemic.

Incidence rates of syphilis have significantly increased in Western countries since 2000, particularly among MSM. This study aimed to analyse trends and characteristics of syphilis cases diagnosed by a sentinel center for the surveillance of sexually transmitted infection in Italy, over a 30-year period. Demographical, behavioural and clinical characteristics of syphilis cases diagnosed from 1991 to 2022 were analysed, overall and by transmission category. Temporal trends in syphilis cases, overall and by transmission category, were assessed using joinpoint regression model. Multivariable logistic regression was performed for the last decade of observation (2011-2022) to assess the associations between syphilis diagnoses and transmission category, nationality and HIV status. A total of 3,093 syphilis cases were diagnosed, most of which among MSM (1,994, 64.5%). HIV prevalence was significantly higher among MSM than men who have sex with women (MSW) and women who have sex with men (WSM) (30.8% vs. 12.7% and 5.8%, respectively). Joinpoint regression analysis highlighted a significant increase in syphilis cases during 2000-2005 both overall and among MSM (p < 0.01), non-Italian born (p = 0.02) and PLWH (p < 0.01). MSM with syphilis differed significantly from non-MSM in terms of age, STI and HIV history. Among syphilis cases, PLWH were more likely to be MSM, older and with previous STI. Syphilis still represents a major public health concern, particularly among MSM. Even populations with lower transmission rates, such as WSM and MSW, experienced increasing trends in diagnoses, potentially promoted by epidemiological bridging mechanisms involving MSM and MSW. Global efforts are still required to end this epidemic.