San Francisco has seen a sharp drop in sexually transmitted infections, with health officials pointing to prevention efforts and a post-exposure antibiotic as key factors.

New data from the San Francisco Department of Public Health show syphilis cases fell 24% in 2025 compared with the year before, while instances of chlamydia dropped 18% and gonorrhea cases declined 5%.

The figures were released on Monday to mark the start of National Sexually Transmitted Infection Awareness Week.

The declines were most pronounced among men who have sex with men and transgender women — populations that have historically been hit the hardest.

Officials say a major driver of the drop is the growing use of doxycycline post-exposure prophylaxis, or doxy-PEP, a treatment taken after sex to help prevent certain bacterial STIs.

“STI prevention is a key priority for SFDPH, and we are thrilled to see that doxy-PEP is making a difference in our communities,” said Daniel Tsai, the city’s director of health.

The findings build on earlier research from San Francisco and Kaiser Permanente Northern California, which found doxy-PEP can significantly reduce syphilis and chlamydia rates, particularly among gay and bisexual men and transgender women, according to the San Francisco Chronicle.

Still, officials stressed the progress isn’t a cure-all.

“We are excited to see the progress being made in lowering STI diagnoses in San Francisco,” said SF Health Officer Dr. Susan Philip. “We encourage the public to keep up the momentum by taking actions — such as getting tested — to protect their sexual health.”

Dr. Stephanie Cohen, who oversees STI and HIV prevention and control for the department, said the shift reflects years of work across the city’s health system.

“The remarkable drop in STI cases in San Francisco is due in large part to the trailblazing work that made the rollout of doxy-PEP possible,” she said.

Testing and treatment are available through city clinics and other programs, including for people without insurance, the department said.