Decreasing trends of syphilis among people with HIV at a university hospital before implementation of doxycycline prophylaxis for syphilis: implications for targeted syphilis prevention.

Objectives: Syphilis remains a public health challenge, particularly among people with HIV (PWH). This study aimed to examine the trends of syphilis and associated factors among PWH in Taiwan, 2016-2023, before the implementation of doxycycline postexposure prophylaxis (DoxyPEP).

Methods: PWH aged 18 years or older who sought HIV care at a university hospital and had at least two serological tests for syphilis during the study period were included. Annual incidence rates of syphilis were calculated as the number of new syphilis cases per 100 person-years of follow-up (PYFU), while the prevalence was defined as the proportion of PWH who had a positive rapid plasma reagin (RPR) titre. Reinfection was defined as a ≥4 fold increase in RPR titre following a prior syphilis diagnosis. Multivariable logistic regression was used to identify factors associated with syphilis acquisition.

Results: Among 3828 PWH, a total of 3201 incident syphilis cases were recorded during a total of 23 385.1 PYFU. The incidence rate decreased significantly from 16.78 per 100 PYFU in 2016 to 11.14 per 100 PYFU in 2023, a 33.6% reduction. The prevalence peaked at 45.0% in 2019 before declining to 41.6% in 2023. Reinfections constituted 66.3-85.0% of incident cases annually. Factors associated with acquiring syphilis included younger age (adjusted OR (AOR), per 10-year increase, 0.71; 95% CI, 0.67 to 0.75), men who have sex with men (AOR, 1.75; 95% CI, 1.32 to 2.32), a previous syphilis history (AOR, 7.26; 95% CI, 6.48 to 8.14) and no follow-up RPR data in the preceding year(s) (AOR, 3.02; 95% CI, 2.08 to 4.38).

Conclusions: While the declines in incidence and prevalence of syphilis among PWH before the implementation of DoxyPEP were likely driven by an ageing population in Taiwan, regular serological testing for syphilis remains imperative for early diagnosis and treatment of syphilis to prevent further transmission.