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CROI 2024: Doxy-PEP greatly reduces syphilis and chlamydia cases

March 6, 2024

A San Francisco Department of Public Health (SFDPH) analysis showed that the number of chlamydia and early syphilis infections among men who have sex with men (MSM) and transgender women declined more than 50% over the 13 months since November 2022 when the Department released guidelines for the use of doxycycline post-exposure prophylaxis (doxy-PEP).

The findings were presented at the Conference on Retroviruses and Opportunistic Infections (CROI) on March 4, 2024 in Denver, Colorado.

• City officials tracked monthly rates of chlamydia, gonorrhea and early syphilis before and after the introduction of doxy-PEP in November 2022. They also compared the numbers with the rate of infections in cisgender women.
• Thirteen months after SFDPH’s first-in-the-nation doxy-PEP guidance was issued, monthly reported chlamydia and early syphilis infections among MSM and transgender women decreased by 50% and 51% respectively.
• These findings are the first to measure the effect of doxy-PEP at the population level; SFDPH partnered with the Getting to Zero, San Francisco consortium on this analysis.
• While the results were promising regarding chlamydia and early syphilis, there was no decline in gonorrhea infections among MSM and transgender woman.
• Authors also noted that population-level trends in STIs are complex and can be impacted by multiple factors, including behavioral changes (such as following the 2022 mpox outbreak), and disruptions in STI testing during the COVID-19 pandemic.

The San Francisco AIDS Foundation (SFAF) was one of the first organizations in the U.S. to roll out Doxy-PEP, beginning in late 2022 when it was offered to all active PrEP clients at their visits at the Magnet clinic. SFAF medical director Dr. Hyman Scott reported that there was high uptake among clients and that bacterial STIs decreased by nearly 60% in less than a year at SFAF’s clinic. The decline was highest for syphilis (78%) and chlamydia (67%).

In San Francisco, doxy-PEP is recommended for cis men and trans women who have had a bacterial STI in the past year and who have had condomless anal or oral sexual contact with at least one cis male or trans female partner in the past year. The guidance also recommends that a broader group be offered doxy-PEP, including cis men, trans men and trans women who report having multiple cis male or trans female sex partners in the prior year, even if they have not previously been diagnosed with an STI.

Two 100 mg pills of doxycycline should be taken ideally within 24 hours, but no later than 72 hours after condomless sex. As of December 2023, over 3,500 people in San Francisco have been prescribed doxy-PEP.

Doxy-PEP is not recommended for cis-gender women because there is not yet evidence to suggest it is effective for them.

Sources:

(2024, March 4) SF.gov. News. Sexual Health Prevention Tool Associated with Declines in Sexually Transmitted Infections in San Francisco. https://www.sf.gov/news/sexual-health-prevention-tool-associated-declines-sexually-transmitted-infections-san

(2024, March 5). HIV.gov. Doxy-PEP for STIs and HIV Vaccine Research: Dr. Dieffenbach's First Update from CROI 2024. https://www.hiv.gov/blog/doxy-pep-for-stis-and-hiv-vaccine-research-dr-dieffenbach-s-first-update-from-croi-2024