Risk Factors and Incidence of Sexually Transmitted Infections in the Swiss HIV Cohort Study

BACKGROUND: Sexually transmitted infections (STIs) are common among people with human immunodeficiency virus (PWH), but there are limited data about risk factors and incidence of STIs in large, representative cohort studies. METHODS: We assessed incidence and risk factors of STIs reported by treating physicians within the Swiss HIV Cohort Study (SHCS). Sexually transmitted infections and demographic, clinical, and behavioral characteristics were prospectively collected at 6-month follow-up visits between October 2017 and November 2019. We used multilevel Poisson regression to assess incidence rate ratios of different STIs. RESULTS: Among 10 140 study participants, a total of 1634 STIs in 1029 SHCS participants were reported over 17 766 person-years of follow up (PYFUP). The overall incidence of any reported STI was 91.9 per 1000 PYFU (95% confidence interval [CI], 85.8 –98.5). Among the 1634 STI episodes, there were 573 (35.1%) incident cases of syphilis, 497 gonorrhea (30.4%), and 418 chlamydia (25.6%). Men who have sex with men (MSM) younger than 50 years represented 21% of the study population, but accounted for 61% of reported STIs. Male sex (adjusted incidence rate ratio [aIRR], 2.03; 95% CI, 1.36–3.02), MSM (aIRR, 3.62; 95% CI, 2.88–4.55), age group 18–34 years (aIRR, 1.78; 95% CI, 1.51–2.10), history of sexual relationships with occasional partners (aIRR, 6.87; 95% CI, 5.40–8.73), and reporting injecting drug use (aIRR, 2.48; 95% CI, 1.91–3.23) were associated with a higher risk of incident STIs. CONCLUSIONS: Sexually transmitted infections were frequent among PWH and varied considerably between age and risk groups. Screening programs and recommendations for STI testing need to be adapted according to risk factors and demographic characteristics.