Effects of HIV Pre-Exposure Prophylaxis on High-Risk Sexual Behaviors in Men Who Have Sex With Men

Investigators conducted a study to assess the rates of high-risk sexual behavior and sexually transmitted infections among men who have sex with men before and after the introduction of HIV pre-exposure prophylaxis.

Among men who have sex with men (MSM) living in the Netherlands, high-risk sexual behavior and gonorrhea diagnoses increased after the advent of HIV pre-exposure prophylaxis (PrEP), according to results of a prospective cohort study published in Sexually Transmitted Infections.

Investigators analyzed data from a prospective cohort study on MSM who were tested for HIV and other sexually transmitted infections (STI) and completed questionnaires about sexual behavior at biannual clinic visits between 2009 and 2019. All patients included in the study were negative for HIV infection at enrollment. The investigators sought to assess the prevalence of high-risk sexual behavior and incident STI diagnoses among MSM before and after the introduction of PrEP in the Netherlands. To calculate Gini coefficients for diagnoses of gonorrhea, chlamydia, and syphilis in the period before (2009 to mid-2015) and after (mid-2015 to 2009) the introduction of PrEP, investigators developed a sexual behavior risk score predictive of STI diagnosis. A Gini coefficient close to 0 indicated that STIs were homogenously distributed among the population, and close to 1 indicated that STIs were concentrated among patients with increased sexual behavior risk scores.

The investigators analyzed data from 13,473 clinic visits representing a total of 971 patients. The majority (69%) of patients were Dutch and highly educated (77%), the mean age at first clinic visit was 35 (SD, 10) years, and PrEP use was reported by 24% of patients at 758 clinic visits (5%), all of which occurred in 2015.

The investigators performed a multivariable analysis to assess data captured from 12,274 clinic visits representing a total of 959 patients. Among these patients, sexual behavior risk scores ranged between 0.00 (low risk) and 3.61 (high risk), with a mean score of 0.82 (SD, 0.74). Following the introduction of HIV PrEP, the mean sexual behavior risk score increased from 0.63 (SD, 0.62) to 1.01 (SD, 0.81). Of note, the mean sexual behavior score was most increased among patients who reported PrEP use within the past 6 months (1.27; SD, 0.70) compared with those without recent PrEP use (0.73; SD, 0.57).

After the introduction of HIV PrEP, positivity rates for chlamydia and syphilis remained relatively stable, but positivity rates for anal gonorrhea and anal STI were significantly increased.

Among 10,677 clinic visits representing a total of 630 patients, the Gini coefficient for chlamydia increased from 0.37 (95% CI, 0.30-0.43) to 0.43 (95% CI, 0.36-0.49) after the introduction of HIV PrEP. The investigators also noted that the Gini coefficient for syphilis increased from 0.37 (95% CI, 0.19-0.52) to 0.50 (95% CI, 0.32-0.66) after the introduction of PrEP, but the Gini coefficient for gonorrhea remained stable at 0.46 (95% CI, 0.40-0.52).

This study was limited by the small number of syphilis diagnoses among the included patients, which may have resulted in wide CIs for the estimated Gini coefficients.

The investigators suggested that certain MSM subpopulations viewed PrEP as “the ultimate prevention measure” and therefore increased high-risk sexual behaviors once PrEP became available. “Monitoring the impact of increasing PrEP coverage on [high-risk] sexual behavior and STI incidence is of great importance, and improved STI prevention is needed, especially for high-risk MSM,” the investigators concluded.


van Wees DA, Diexer S, Rozhnova G, et al. Quantifying heterogeneity in sexual behaviour and distribution of STIs before and after pre-exposure prophylaxis among men who have sex with men. Sexually Transmitted Infections. Published online October 29, 2021. doi:10.1136/sextrans-2021-055227