Background
Doxycycline for post-exposure prophylaxis (DPEP) is highly effective for preventing bacterial sexually transmitted infections (STIs) in clinical trials; however recent real-world data suggests lack of effectiveness for gonorrhea. We examined the impact of DPEP on STIs (syphilis, chlamydia, and gonorrhea) in clients at a large sexual health clinic in San Francisco, CA, US.
Methods
Starting in 11/30/2022 DPEP was offered to all clients receiving sexual health services. For clients who were prescribed DPEP (Users) for >90 days, we evaluated up to 5 quarters before and after the initial DPEP prescription through 09/24/2024. For clients who were never prescribed DPEP (Non-DPEP users), we evaluated up to 5 quarters before and after 4/2023 – the midpoint (median) quarter for the DPEP initiations across the evaluation period. We fit an interrupted time series (ITS) analysis in which STI rates, overall and by individual STI, were predicted by a three-way interaction between DPEP use, time (in quarters), and DPEP initiation (pre-post DPEP prescription for the DPEP Users, and pre-post median time for the non-DPEP users).
Results
Overall, 4,149 clients (2,419 DPEP users and 1,730 non-DPEP users) were included in the analyses with an average of 3.13 (SD=1.70) quarters of follow-up. The median age range was 30-39 years and most (89%) were cisgender men. Race/ethnicity included 33% White, 24% Hispanic/Latinx, 17% Asian, 13% multiracial, and 4% Black. Almost all (98.7%) were also prescribed HIV pre-exposure prophylaxis. Before initiating DPEP, the DPEP users had significantly higher risk of an STI than non-DPEP users [Odds Ratio (OR)=5.33, 95% Confidence Interval (CI) 4.11-6.90, p<.001); however, after initiation STI rates were similar (OR=1.21, 95%CI 0.86-1.68, p=.280). In a pre-post analysis among DPEP users, STI incidence declined significantly overall (OR=0.28, 95%CI 0.24-0.35, p<.001) and for each STI: chlamydia (OR=0.05; 95%CI 0.11-0.20, p<.001), gonorrhea (OR=0.45; 95%CI 0.39-0.53, p<.001), and syphilis (OR=0.16; 95%CI 0.12-0.21, p<.001). The ITS revealed a significant three-way interaction between DPEP use, time, and DPEP initiation, p<.001.
Conclusions
DPEP uptake continues to increase and bacterial STI incidence among DPEP users declined significantly overall and for each STI including gonorrhea demonstrating sustained high impact of this intervention in a real-world setting. Continued evaluation of DPEP uptake, use, and adherence will be essential as implementation expands.
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