1. In this population intervention study, receipt of HIV preexposure prophylaxis (PrEP) was associated with an increased incidence of STIs in homosexual and bisexual men compared to before PrEP administration.
2. STIs were concentrated in a subgroup of PrEP patients during follow-up.
Evidence Rating Level: 2 (Good)
Study Rundown: HIV pre-exposure prophylaxis (PrEP) is highly effective in reducing HIV contraction among homosexual and bisexual men at highest risk for contracting the virus. However, there remains concern that PrEP may result in behavioral changes that leads to increases in bacterial STIs. In this population intervention study, receipt of HIV PrEP was associated with an increased incidence of STIs in homosexual and bisexual men compared to before PrEP administration. Interestingly, STIs were concentrated in a subgroup of PrEP patients during follow-up.
While this study suggests that there may be behavior changes that lead to increased STI contractions among PrEP users, early adopters of PrEP are typically individuals with already high STI risk. Additionally, the concentration of STIs among a subgroup of patients suggest other risk factors may influence which patients are at higher STI risk. Further, behavioral responses were self-reported, and this may lead to recall or social desirability bias. Finally, some participants may have received STI treatment at clinics not participating in the study.
Relevant Reading: A mobile application to collect daily data on pre-exposure prophylaxis adherence and sexual behaviour among men who have sex with men: use over time and comparability with conventional data collection.
In-Depth [prospective cohort study]: In the Pre-Exposure Prophylaxis Expanded (PrEPX) study, 2981 mostly homosexual and bisexual men were recruited to receive daily HIV PrEP in Victoria, Australia. Individuals who met 1 or more prespecified eligibility criteria based on self-reported HIV risk in the previous 3 months and were predicted to have ongoing HIV risk in the next 3 months were eligible to enroll. Upon enrollment, participants received daily oral tenofovir and emtricitabine for HIV PrEP, quarterly HIV and STI testing, and clinical monitoring. The primary outcome was the incidence of STIs, defined as diagnosis of chlamydia, gonorrhea, or newly identified syphilis. Exploratory outcomes were behavioral risk factors associated with STI diagnosis. Participants were monitored for 3195 person years after enrollment. Median follow-up was 1.19 years. Incidence of any STI diagnosis at follow-up was 91.9 per 100 person-years. In bivariable Cox regression analyses, younger age, use of PrEP and postexposure prophylaxis prior to enrollment, and diagnosis of rectal gonorrhea, rectal chlamydia, or syphilis prior to enrollment were several of the characteristics associated with greater STI risk. Among PrEP-naïve patients, incidence of any STI increased significantly to 94.2 per 100 person-years, Incidence Rate Ratio (IRR) 1.71 (CI95 1.49 to 1.96), 39.1/100 person-years during follow-up. The change in incidence among PrEP-experienced patients to 104.1/100 person-years was not significant.
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