Syphilis seroprevalence and seroconversion among people newly diagnosed with HIV during the pre-antiretroviral therapy period in rural China

Syphilis has a high incidence among people living with HIV (PLHIV), which may be attributable to their similar sexual transmission route. A retrospective cohort study was conducted during the period 2009–2015 to investigate the syphilis seroprevalence and incidence of syphilis seroconversion among newly-diagnosed PLHIV in rural Yunnan, China. Recent HIV infection among PLHIV was identified by BED capture enzyme immunoassay. PLHIV were followed until they initiated antiretroviral therapy. Syphilis serology was conducted at baseline and each follow-up over the study period. Among 2162 participants, the syphilis seroprevalence at baseline was 2.7%, 95% confidence interval (CI) (2.4–3.1). Single and divorced (versus married) (aOR = 2.9, [1.1–7.4]; 5.9, [2.4–14.7], respectively), employed in the service industry (versus unemployed) (2.8, [1.4–5.6]), being diagnosed with HIV in hospitals (versus voluntary counselling and testing) (5.1, [2.0–12.9]), recent HIV infection (17.9, [8.5–37.9]) and inconsistent condom use in the previous three months (versus consistent condom use) (6.2, [2.8–13.4]) were associated with higher risk of syphilis infection at baseline. Participants contributed 1955.4 person-years (PYs) of follow-up, with a median follow-up period of 0.9 years (IQR: 0.5–1.9) and the incidence of syphilis seroconversion was 2.2 (95% CI 1.5–2.9) per 100 PYs. The syphilis seroprevalence at baseline (aHR 3.7, [1.8–7.9]), had a HIV-negative partner at baseline (3.9, [1.5–9.8]) and inconsistent condom use in the last three months at baseline (6.0, [1.4–25.4]) were associated with higher risk of syphilis seroconversion. Our findings indicate that the public health response should be escalated to minimise the spread of syphilis co-infection among PLHIV and reducing condomless sexual behaviours after HIV diagnosis.