Objectives Doxycycline as bacterial sexually transmitted infection (STI) postexposure prophylaxis (DoxyPEP) has shown high efficacy in clinical trials. We evaluated the impact of DoxyPEP on chlamydia (CT), gonorrhoea (GC) and syphilis incidence among pre-exposure prophylaxis (PrEP) users in a sexual health clinic in San Francisco, California, USA. Methods DoxyPEP was offered to all PrEP clients at routine clinical visits starting on 30 November 2022. We included PrEP clients who received DoxyPEP (DoxyPEP users) or never initiated DoxyPEP (non-DoxyPEP users). Among DoxyPEP users, the ‘pre-DoxyPEP’ period was from 1 June 2022 until DoxyPEP initiation, and the ‘post-DoxyPEP’ period started after DoxyPEP initiation through 7 September 2023. STI testing included three sites—GC, CT and early syphilis testing. STI incidence rate ratios (IRRs) per quarter were evaluated using a pre-analysis, post-analysis and a controlled interrupted time series (CITS) analysis, with mixed-effects Poisson regression used to evaluate intervention effects. Results Among 3081 PrEP clients, 1209 (39%) initiated DoxyPEP. During the pre-DoxyPEP period, any STI, CT, GC and syphilis mean quarterly positivity was 18.1%, 9.2%, 8.1% and 2.2% among DoxyPEP users and 7%, 3.2%, 3% and 0.7% among non-DoxyPEP users, respectively. In pre-implementation and post-implementation analysis of DoxyPEP users, DoxyPEP was associated with lower STI incidence for any STI (IRR 0.42, 95% CI 0.24 to 0.74, p=0.003), CT (IRR 0.33, 95% CI 0.23 to 0.46, p<0.001) and syphilis (IRR 0.22, 95% CI 0.07 to 0.54, p=0.001), but not GC (IRR 0.89, 95% CI 0.69 to 1.15, p=0.383). In a CITS analysis, DoxyPEP was associated with a significant decline in any STI incidence (0.67, 95% CI 0.46 to 0.96, p<0.030). Conclusions Observed DoxyPEP uptake reflected strong demand among PrEP users when offered in a clinical setting. Overall, STI incidence declined rapidly after implementation, demonstrating the high impact of this intervention in a real-world setting. Continued evaluation of uptake, adherence and impact on bacterial STIs will be essential as DoxyPEP implementation expands.
David V. Glidden (Wed,) studied this question.