There has been a significant drop in chlamydia and early syphilis infections among men who have sex with men and transgender women after implementing first-in-the-nation guidelines for taking antibiotics after sexual encounters, according to San Francisco health officials.
The San Francisco Department of Public Health's analysis found that 13 months after issuing guidance on using doxycycline post-exposure prophylaxis, or doxy-PEP, monthly reported chlamydia cases fell 50% and early syphilis cases 51% compared with projected levels.
The findings, presented at this week's Conference on Retroviruses and Opportunistic Infections by co-author Madeline Sankaran, marked the first measurement of doxy-PEP's population-level impact. Health officials partnered with the Getting to Zero consortium on the analysis.
"This shows that this promising prevention tool has the impact to help turn the curve on the epidemic of STIs that we have been facing," said Dr. Grant Colfax, director of the department, in a statement. “San Francisco continues to be at the forefront of innovation, as well as a model when it comes to protecting the sexual health of populations traditionally affected by STIs."
According to a federal Centers for Disease Control report released last year, more than 2.5 million cases of syphilis, gonorrhea and chlamydia were reported in the United States in 2022.
Syphilis cases increased 80% over the past five years, but reported chlamydia cases were relatively flat, and reported gonorrhea cases fell by nearly 9% in 2022.
San Francisco issued the doxy-PEP guidance in October 2022 following a clinical trial showing the antibiotic could reduce the odds of getting syphilis, gonorrhea and chlamydia by about two-thirds if taken after sex.
The guidelines recommend men who have sex with men and transgender women who had condomless sexual contact take two 100-milligram doxycycline pills within 72 hours. It's also offered preventively to those with multiple recent partners, even without a prior infection.
By December 2023, over 3,500 people had been prescribed doxy-PEP in San Francisco.
The analysis found no decline in gonorrhea cases, however. And officials cautioned other factors like behavioral changes during the 2022 monkeypox outbreak and Covid testing disruptions could have influenced STI trends.
Still, Dr. Susan Philip, San Francisco's health officer, said the results demonstrate how "public health experts, researchers and community" can address "critical health issues" through innovative approaches.
Health officials encouraged those without a medical provider to visit the city's sexual health clinic to access doxy-PEP.