Abstract Body


In October 2022, the San Francisco (SF) Department of Public Health disseminated guidelines through community and public health networks recommending doxycycline post-exposure prophylaxis (doxy-PEP) for men who have sex with men (MSM) and transgender women (TGW) with a history of sexually transmitted infections (STIs) or multiple sex partners. Doxy-PEP’s effect on population-level incidence of STIs is unknown.


To monitor doxy-PEP uptake at sentinel sites, we tracked the quarterly number of new patients initiating doxy-PEP from three high-volume SF sexual health clinics. To assess the ecological association between doxy-PEP program implementation and citywide STI incidence, we conducted interrupted time series analyses on monthly reported SF cases of chlamydia (CT), gonorrhea (GC), and early syphilis (ES), among MSM/TGW before (7/1/21–10/31/22) and after (11/1/22–11/30/23) release of doxy-PEP guidance, and used autoregressive integrated moving average (ARIMA) models to forecast expected post-period monthly case counts in the absence of doxy-PEP. Observed case counts were based on citywide surveillance data. Analyses were repeated for monthly CT case counts among cis women for comparison.


From 11/1/22 to 9/30/23, 3,288 MSM/TGW initiated doxy-PEP at the three sentinel clinics. Citywide, the number of monthly reported CT (-6.7%/month, p<0.0001) and ES (-3.12%/month, p<0.0001) cases among MSM/TGW decreased significantly after the release of doxy-PEP guidelines compared to model forecasts (Figure). By the end of the 13-month post-period, CT and ES cases decreased 51% (95% CI: 39%-60%) and 50% (95% CI: 38%-59%), respectively, compared to expected counts in November 2023. No significant change in GC cases was seen (p=0.087). Among cis women, the number of monthly reported CT cases in the post-period increased significantly (2.43%/month, p<0.01).


Release of SF doxy-PEP guidelines and early implementation at high volume clinics were associated with a substantial sustained decrease in reported SF cases of CT and ES, but not GC, among MSM/TGW over a 13-month period. Other factors, including changes in screening and sexual practices (e.g., in response to mpox), may have contributed to observed trends. Future analyses are planned with extended post-period data to determine whether observed trends continue to align with citywide doxy-PEP uptake and to assess for demographic disparities in doxy-PEP uptake and STI incidence.