Clinical and serological outcomes of syphilis: an 18-year retrospective cohort study on predictors of treatment response and seroreversion in Türkiye.

purposeDespite established protocols, the global resurgence of syphilis remains a public health challenge, with outcomes influenced by disease stage and host factors. This study described 18-year epidemiological trends and identified predictors of serological treatment response and long-term seroreversion.

methodsWe retrospectively analyzed 503 adults diagnosed with syphilis between 2005 and 2022 and classified disease stages according to CDC criteria. Treatment response was defined as a ≥ 4-fold decline in rapid plasma reagin (RPR) titers within 12 months for early-stage and 24 months for late-stage syphilis, while seroreversion was defined as a non-reactive RPR. Overall, 157 patients were included in the treatment-response analysis and 159 in the seroreversion analysis, the latter including two additional patients who achieved seroreversion before treatment-response assessment. Independent predictors were identified using multivariable logistic regression.

resultsSyphilis cases increased significantly after 2015, with late-stage disease accounting for 75.7% (n = 381) of diagnoses. Early syphilis rose from 10.5% (2005-2015) to 30.2% after 2015 (p < 0.001). Among patients with available HIV test results, 29.4% (134/456) of cases were in people with HIV. Early-stage syphilis was more frequent in people living with HIV (PLWH) than in HIV-negative individuals (32% vs. 20.1%). Among patients with follow-up, 75.2% (118/157) achieved a serological response. In multivariate analysis, late-stage syphilis was a negative predictor of response (OR 0.22, 95% CI 0.07-0.76; p = 0.016), while baseline RPR titers ≥ 1:8 were a strong positive predictor (OR 8.18, 95% CI 1.72-38.85; p = 0.008). HIV status was not independently associated with response (p > 0.05). Seroreversion occurred in 35.8%, with no independent predictors identified.

conclusionsThe syphilis burden has grown, driven by delayed diagnosis and late-stage predominance despite recent trends toward earlier detection. In this cohort, disease stage and baseline RPR titers were stronger predictors of serological response than HIV status. The higher frequency of early-stage diagnosis in PLWH is consistent with the potential impact of intensified screening and may reflect differences in healthcare engagement and testing practices compared with the general population.