A Prospective Incidence Study on Sexually Transmitted Infections and HIV in Men Who Have Sex with Men with or without Use of Pre-Exposure-Prophylaxis

While pre-exposure prophylaxis (PrEP) can prevent HIV acquisition, associated behavioral changes may increase risk of acquiring other sexually transmitted infections (STIs).

The prospective, multicenter BRAHMS study enrolled HIV-negative men who have sex with men (MSM) aged 18-55 reporting increased risk to acquire STI. At three-month intervals for up to 12 months, participants answered questionnaires, underwent site-specific screening for Chlamydia trachomatis (CT), Mycoplasma genitalium (MG), Neisseria gonorrhoeae (NG), and syphilis. We computed three-month incidence rates and incidence rate ratios, and we employed multi-level mixed effects logistic regression to determine odds ratios (ORs) and 95%-confidence intervals (CIs) for factors associated with any incident STI.

Mean age of 1,017 participants was 33 years, 54.7% used PrEP at enrollment, 83.7% reported PrEP use overall. Any STI was diagnosed in 71.8% (CT:40.4%; MG:38.5%; NG:36.0%; syphilis:10.1%; HIV:0.5%). PrEP users exhibited higher prevalence for anorectal infections with CT (35.3% vs. 20.5%, p<0.05), MG (31.4% vs. 23.5%, p<0.05), and NG (26.1% vs. 16.9%, p<0.05). CT incidence decreased from 46.8 cases/100 person years (PY) to 35.7 (-23.7%, p<0.05), NG incidence decreased from 4.6 cases/100PY to 30.7 (-26.2%, p<0.05). MG and syphilis incidence remained stable.

Factors independently associated with STI incidence included symptoms (OR=1.85;CI:1.46-2.34), condomless anal sex with >5 casual partners (OR=1.79;CI:1.49-2.14), recreational drug use (OR=1.76;CI:1.46-2.12), being born abroad (OR=1.49;CI:1.19-1.87), PrEP use (OR=1.29;CI:1.05-1.58) and having a moderately or largely increased self-perceived risk of HIV (OR=1.26;CI:1.03-1.53 and OR=1.33;CI:1.02-1.74, respectively).

PrEP use was associated with increased STI risk in our cohort. CT and NG incidence decreased in a structured test-and-treat setting.