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.

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Background: Pre-exposure prophylaxis (PrEP) is the use of HIV anti-retroviral therapy to prevent HIV transmission in people at high risk of HIV acquisition. PrEP is highly efficacious when taken either daily, or in an on-demand schedule. In Australia co-formulated tenofovir-emtricitabine is registered for daily use for PrEP, however, this co-formulation is not listed yet on the national subsidized medicines list. We describe a study protocol that aims to demonstrate if the provision of PrEP to up to 3800 individuals at risk of HIV in Victoria, Australia reduces HIV incidence locally by 25% generally and 30% among GBM.Methods: PrEPX is a population level intervention study in Victoria, Australia in which generic PrEP will be delivered to 3800 individuals for up to 36 months. Study eligibility is consistent with the recently updated 2017 Australian PrEP guidelines. Participants will attend study clinics, shared care clinics, or outreach clinics for quarterly HIV/STI screening, biannual renal function tests and other clinical care as required. Study visits and STI diagnoses will be recorded electronically through the ACCESS surveillance system. At each study visit participants will be invited to complete behavioral surveys that collect demographics and sexual risk data. Diagnosis and behavioral data will be compared between PrEPX participants and other individuals testing within the ACCESS surveillance system. A subset of participants will complete in depth surveys and interviews to collect attitudes, beliefs and acceptability data. Participating clinics will provide clinic level data on implementation and management of PrEPX participants. The population level impact on HIV incidence will be assessed using Victorian HIV notification data.Discussion: This study will collect evidence on the real world impact of delivery of PrEP to 3800 individuals at risk of acquiring HIV in Victoria. This study will provide important information for the broader implementation of PrEP planning upon listing of the tenofovir-emtricitabine on the national subsidized list of medicines. The study is registered on the Australian New Zealand Clinical Trials Registry (ACTRN12616001215415)