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Importance Emerging evidence suggests that risk of bacterial sexually transmitted infections (STIs) increases among gay and bisexual men following initiation of HIV preexposure prophylaxis (PrEP). Objective To describe STI incidence and behavioral risk factors among a cohort of predominantly gay and bisexual men who use PrEP, and to explore changes in STI incidence following PrEP commencement. Design, Setting, and Participants The Pre-exposure Prophylaxis Expanded (PrEPX) Study, a multisite, open-label intervention study, was nested within the Australian Collaboration for Coordinated Enhanced Sentinel Surveillance (ACCESS) clinic network. A total of 4275 participants were enrolled (July 26, 2016–April 1, 2018) in Victoria, Australia. Of these, 2981 enrolled at 5 ACCESS clinics (3 primary care, 1 sexual health, and 1 community-based HIV rapid testing service), had at least 1 follow-up visit, and were monitored until April 30, 2018. Exposures Upon enrollment, participants received daily oral tenofovir disoproxil fumurate and emtricitabine for HIV PrEP, quarterly HIV and STI testing, and clinical monitoring. Main Outcomes and Measures The primary outcome was incidence of chlamydia, gonorrhea, or syphilis. Incidence rates and hazard ratios describing behavioral risk factors of STI diagnosis were calculated. Incidence rate ratios (IRRs), adjusted for change in testing frequency, described changes in STI incidence from 1-year preenrollment to study follow-up among participants with preenrollment testing data (n = 1378). Results Among the 2981 individuals (median age, 34 years [interquartile range, 28-42]), 98.5% identified as gay or bisexual males, 29% used PrEP prior to enrollment, 89 (3%) withdrew and were censored at date of withdrawal, leaving 2892 (97.0%) enrolled at final follow-up. During a mean follow-up of 1.1 years (3185.0 person-years), 2928 STIs were diagnosed among 1427 (48%) participants (1434 chlamydia, 1242 gonorrhea, 252 syphilis). STI incidence was 91.9 per 100 person-years, with 736 participants (25%) accounting for 2237 (76%) of all STIs. Among 2058 participants with complete data for multivariable analysis, younger age, greater partner number, and group sex were associated with greater STI risk, but condom use was not. Among 1378 participants with preenrollment testing data, STI incidence increased from 69.5 per 100 person-years prior to enrollment to 98.4 per 100 person-years during follow-up (IRR, 1.41 [95% CI, 1.29-1.56]). After adjusting for testing frequency, the increase in incidence from 1 year preenrollment to follow-up was significant for any STI (adjusted IRR, 1.12 [95% CI, 1.02-1.23]) and for chlamydia (adjusted IRR, 1.17 [95% CI, 1.04-1.33]). Conclusions and Relevance Among gay and bisexual men using PrEP, STIs were highly concentrated among a subset, and receipt of PrEP after study enrollment was associated with an increased incidence of STIs compared with preenrollment. These findings highlight the importance of frequent STI testing among gay and bisexual men using PrEP.

Background To determine participants’ human immunodeficiency virus (HIV) risk, the Australian preexposure prophylaxis (PreEPX) trial used 6 eligibility criteria derived from the US Centers for Disease Control and Prevention PrEP guidelines. Participants who fulfilled no eligibility criteria could be enrolled if clinically assessed to need PrEP. This study evaluated whether PREPX eligibility criteria correlated with biological HIV risk markers—namely, syphilis, anorectal chlamydia, or anorectal gonorrhea (sexually transmitted infections [STIs]). Methods We calculated adjusted odds ratios (aORs) to assess whether eligibility criteria predicted STI diagnoses at enrollment. Results We included 1774 participants, of whom 10.2% tested positive for STIs. Eligibility criteria predicted STI diagnoses as follows: (1) aOR 2.5 (95% confidence interval [CI], 1.4–4.4) for condomless anal intercourse (CLAI) with an HIV-positive regular sexual partner (RSP) with detectable viral load; (2) aOR 1.8 (95% CI, 1.3–2.5) for receptive CLAI with casual sexual partners; (3) aOR 1.8 (95% CI, 1.3–2.5) for previous STIs; (4) aOR 2.1 (95% CI, 1.4–3.0) for methamphetamine use; (5) aOR 0.8 (95% CI, .6–1.1) for unsuccessful condom use; and (6) aOR 1.0 (95% CI, .7–1.4) for insertive CLAI when uncircumcised. Of participants enrolled outside eligibility criteria, 7.1% had STIs. Conclusions Eligibility criteria 1–4 predicted diagnoses of STIs, but eligibility criteria 5 and 6 did not. Our findings support the use of PrEP eligibility criteria recommended in current guidelines. Participants enrolled outside the eligibility criteria had substantial prevalence of STIs, suggesting that people who request PrEP but do not fulfill eligibility criteria may nonetheless need PrEP., The PrEPX trial used eligibility criteria based on the US Centers for Disease Control and Prevention PrEP guidelines. We evaluated whether these eligibility criteria correlated with biological human immunodeficiency virus (HIV) risk markers—namely, syphilis, anorectal chlamydia, and anorectal gonorrhea.