Diverging trends in incidence of HIV versus other sexually transmitted infections in HIV-negative MSM in Amsterdam

Objectives: We investigated changes in incidence rates of HIV and sexually transmitted infections (STIs) and trends in sexual behavior in MSM from 2009 to 2017. Design: Open prospective cohort study. Methods: HIV-negative MSM enrolled in the Amsterdam Cohort Studies were included. Participants semiannually completed a questionnaire on sexual behavior and were tested for HIV-1, syphilis, and urethral, anal and pharyngeal chlamydia and gonorrhea. Time trends in incidence rates were analyzed using exponential survival models. Results: During follow-up, 42 of 905 MSM acquired HIV. The HIV incidence rate was 1.9/100 person-years [95% confidence interval (CI) 1.0-3.7] in 2009 and decreased to 0.5/100 person-years (95% CI 0.2-1.4) in 2017 (P = 0.03). The largest decrease was observed in participants aged at least 35 years (P = 0.005), while the trend remained stable in 18-34 year olds (P = 0.4). The incidence rate for any bacterial STI was 16.8/100 person-years (95% CI 13.4-21.0) in 2010, and increased to 33.1/100 person-years (95% CI 29.0-37.9) in 2017 (P < 0.001). Between 2009 and 2017, the percentage reporting condomless anal sex with casual partners increased from 26.9 to 39.4% (P < 0.001), and the mean number of casual partners from eight (95% CI 8-8) to 11 (95% CI 10-11) (P = 0.05). Condomless anal sex with steady partner(s) remained stable over time (P = 0.5). Conclusion: Among MSM in Amsterdam, incidence rates of HIV versus other STI show diverging trends. The increase in STI incidence coincides with a decrease in condom use with casual partners. The decrease in HIV incidence, despite increased sexual risk behavior, suggests that other HIV prevention methods have been successful in reducing HIV transmission among MSM.