Presentation (CTI)

OBJECTIVES: The optimal approach to implementing doxycycline post-exposure prophylaxis (doxy-PEP) to prevent bacterial sexually transmitted infections (STIs) among Australian men who have sex with men remains uncertain, largely due to concerns about antimicrobial resistance and cost-effectiveness.
METHODS: We developed an individual-based transmission model calibrated to Australian national surveillance data to evaluate five targeted doxy-PEP strategies compared with a base-case scenario from 2025 to 2034. A multi-criteria ranking framework was applied to assess epidemiological impact, antimicrobial resistance outcomes, and economic performance.
RESULTS: All evaluated doxy-PEP strategies reduced overall STI incidence by 13.0% to 47.8% and were cost-saving compared with the base case. Despite these benefits, all strategies produced higher proportions of high-level tetracycline resistance than the already elevated baseline projection of 73.5% by 2034. Targeting all HIV pre-exposure prophylaxis users resulted in the highest projected resistance (97.4%), whereas the syphilis-diagnosis-based strategy yielded the lowest (81.2%). The syphilis-focused strategy reduced overall STIs by 16.4%, achieved the highest benefit-cost ratio (9.2), and ranked first in 9 of the 11 evaluation criteria.
CONCLUSIONS: Doxy-PEP is an effective and cost-saving intervention for reducing bacterial STIs in Australia. Among the strategies assessed, targeting individuals with recent syphilis diagnosis offers the most balanced approach, optimally maximising epidemiological benefit while minimising resistance and economic risks.