Bacterial sexually transmitted infections are concentrated in subpopulations of men who have sex with men using HIV pre-exposure prophylaxis.

Objective: Studies have shown varying trends in incidence of sexually transmitted infections (STIs) among individuals using HIV pre-exposure prophylaxis (PrEP). Characterization of individuals at increased risk for STIs may offer an opportunity for targeted STI screening.

Design: Group-based trajectory modeling.

Methods: We screened participants from the AMPrEP demonstration project (2015-2020) for urogenital, anal, and pharyngeal chlamydia and gonorrhea, and syphilis every 3 months and when needed. We identified trajectories of STI incidence within individuals over time and determinants of belonging to a trajectory group. We calculated cumulative proportions of STIs within STI trajectory groups.

Results: Three hundred and sixty-six participants with baseline and at least one screening visit during follow-up were included (median follow-up time = 3.7 years [interquartile range, IQR = 3.5-3.7]). We identified three trajectories of STI incidence: participants with a mean of approximately 0.1 STIs per 3 months ('low overall', 52% of the population), participants with a mean 0.4 STI per 3 months ('medium overall', 43%), and participants with high and fluctuating (between 0.3 and 1 STIs per 3 months) STI incidence ('high and fluctuating', 5%). Participants in the 'low overall' trajectory were significantly older, and reported less chemsex and condomless anal sex with casual partners than participants in the other trajectories. Participants in the 'high and fluctuating' and 'medium overall' groups accounted for respectively 23 and 64% of all STIs observed during follow-up.

Conclusions: STI incidence was concentrated in subpopulations of PrEP users who were younger, had more chemsex and condomless anal sex. Screening frequency for STIs could be reduced for subpopulations with low risk for incident STIs.