Population-Level Effectiveness of HIV Pre-exposure Prophylaxis Among MSM and Transgender Persons With Bacterial Sexually Transmitted Infections

Pre-exposure prophylaxis (PrEP) is highly efficacious, but its effectiveness may be limited by poor adherence or discontinuation. Our objective was to estimate the effectiveness of real-world PrEP use in a population at increased risk of HIV infection. SETTING: King County, Washington. METHODS: We conducted a retrospective cohort study using sexually transmitted infection (STI) partner services (PS) interview data collected January 2014–August 2018 in King County, Washington, USA. During PS interviews, men who have sex with men and transgender persons who have sex with men were asked if they were taking PrEP. We linked STI PS data to HIV surveillance data to estimate HIV incidence among self-reported PrEP users vs. nonusers using Cox proportional hazards regression, adjusting for age, race/ethnicity, and calendar year. RESULTS: Among 4368 individuals, 1206 (28%) were taking PrEP at the time of the PS interview. The median observation time was 14 months (interquartile range 6–23 months). Five (0.4%) of 1206 PrEP users and 97 (3%) of 2162 PrEP nonusers were subsequently diagnosed with HIV (P < 0.001). HIV incidence was lower among PrEP users than nonusers [0.17 vs. 1.86 cases per 100 person-years, adjusted hazards ratio 0.21 (95% confidence interval: 0.08 to 0.58)]. Latinx ethnicity, Native Hawaiian/Pacific Islander ethnicity, gonorrhea, and syphilis were also independently associated with higher HIV risk. CONCLUSIONS: Self-reported PrEP use was associated with a 79% reduction in HIV incidence among men who have sex with men and transgender persons who have sex with men with STIs in King County.