A Canadian study finds that pre-exposure prophylaxis uptake was associated with a higher incidence of gonorrhea, but not other bacterial sexually transmitted infections, among gay, bisexual, and other men who have sex with men in Ontario.
The research, published in Annals of Family Medicine, analyzed data from 535 HIV-negative, cisgender gay, bisexual, and other men who have sex with men (GBM) participating in the iCruise online study from 2017 to 2018. The study followed participants for a median of 3.3 months, during which 13.1% took pre-exposure prophylaxis (PrEP).
Using marginal structural models to account for time-varying confounding, the study found that PrEP uptake was associated with a 4-fold increase in gonorrhea incidence (incidence rate ratio [IRR], 4.00; 95% CI, 1.67-9.58) compared with no PrEP use. Notably, the unadjusted analysis had initially shown a higher gonorrhea risk (IRR, 7.05; 95% CI, 3.29-15.1) before adjusting for confounders. PrEP use was not significantly associated with increased incidence of chlamydia (IRR, 1.22; 95% CI, 0.53-2.81), syphilis (IRR, 1.05; 95% CI, 0.28-3.92), or bacterial STIs overall (IRR, 1.86; 95% CI, 0.86-4.04).
Over the 1,623.5 person-months of follow-up, the crude incidence rates per 100 person-months were 5.5 (95% CI, 4.5-6.8) for any bacterial STI, 2.5 (95% CI, 1.8-3.4) for chlamydia, 1.8 (95% CI, 1.2-2.6) for gonorrhea, and 1.2 (95% CI, 0.8-1.9) for syphilis.
Methodology and Analysis
Data came from the iCruise study, an online longitudinal survey of Ontarian GBM conducted between July 2017 and April 2018. Participants, aged 18 or older, completed weekly diary surveys for up to 12 weeks. PrEP use and bacterial STI incidence (chlamydia, gonorrhea, and syphilis) were self-reported.
Researchers employed marginal structural models with inverse probability of exposure and attrition weights to adjust for time-varying confounding. Sensitivity analyses, including quantitative bias analysis, were conducted to assess the impact of potential nondifferential outcome misclassification.
Participant Characteristics
The average age of participants was 34 years (SD, 12.8), with 58.8% identifying as White and 69.0% identifying as gay. Additionally, 85.2% of participants had access to a primary care clinician, and 59.6% had university or postgraduate education.
Before the study, 18.1% of participants reported condomless anal sex, and 36.1% had undergone STI testing in the previous three months. During the study, participants averaged 3.4 anal sex partners before initiating PrEP, which decreased to 1.2 after PrEP initiation. Condomless anal sex prevalence was similar before and after PrEP uptake (57.1% vs. 54.3%).
Study Limitations
The authors noted several limitations, including reliance on self-reported STI diagnoses and PrEP use, potential residual confounding, and a short follow-up period. Self-selection bias due to recruitment via sex-seeking social media sites was also considered.
Despite these limitations, the findings supported current guidelines recommending the integration of gonorrhea screening with PrEP services. The study highlights the need for primary care practitioners to provide comprehensive sexual health care, including PrEP prescribing and support for ancillary services.
The authors declared no competing interests.
