Thirty-Year Trend of Syphilis During the Periods of the Resurgence, HIV Risk Compensation, and COVID-19 Pandemic.

PURPOSE: Incidence rates of syphilis have significantly increased in Western countries since 2000, particularly among men who have sex with men (MSM). This study aimed to analyze trends and characteristics of syphilis cases diagnosed by a sentinel center for the surveillance of sexually transmitted infection (STI) in Italy, over a 30-year period.

METHODS

Demographical, behavioral, and clinical characteristics of syphilis cases diagnosed from 1991 to 2022 were analyzed, 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.

RESULTS

A total of 3093 syphilis cases were diagnosed, most of which among MSM (1994, 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 people living with HIV ( P < 0.01). In terms of age, STI, and HIV history, MSM with syphilis differed significantly from non-MSM. Among syphilis cases, people living with HIV were more likely to be MSM, older, and with previous STI.

CONCLUSIONS

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.