Syphilis and chlamydia infections were halved among men who have sex with men and transgender women in San Francisco a year after the city rolled out a new antibiotic medication.
The antibiotic is called doxycycline, and the strategy that uses it to stem sexually transmitted infections is called doxycycline post-exposure prophylaxis, or doxy-PEP for short. In October 2023, the Centers of Disease Control and Prevention released draft guidelines for doxy-PEP. But, encouraged by early clinical trials of the strategy, the San Francisco Department of Public Health started recommending doxy-PEP a year before the CDC’s guidelines were published.
Gay and bisexual men and transgender women in San Francisco who had a history of STIs or multiple sex partners were given a stock of doxycycline and were asked to take two 100-milligram pills within 72 hours of having unprotected sex.
San Francisco city officials tracked monthly rates of chlamydia, gonorrhea, and early syphilis before and after doxy-PEP was rolled out in November 2022. Over a 13-month period, new cases of chlamydia and early syphilis across San Francisco dropped by 50 percent, but rates of gonorrhea did not notably change.
Meanwhile, cases of chlamydia in cisgender women rose. With the majority of STIs occurring in cisgender women, studies of doxy-PEP working in that population are needed. Currently, studies support the implementation of doxy-PEP only in gay and bisexual men, and transgender women.
Still, doxy-PEP presents a promising strategy to curb STI rates in the United States. In 2022, more than 2.5 million cases of syphilis gonorrhea and chlamydia were reported in the US. Syphilis specifically has reached the highest rate of new infections recorded since 1950, according to the CDC.
But as with the introduction of any new medication there are questions about the side effects of the widespread use of doxycycline, particularly with regards to antibiotic resistance. However, the current limited data suggest that doxy-PEP does not significantly increase antibiotic resistance in people who take it. However, the CDC and other medical organizations are monitoring the results, and continued evaluation of doxy-PEP’s implementation will be essential.
In any case, doxy-PEP is a huge development in the effort to reduce STIs in the United States. Jorge Roman, the Senior Director of Clinical Services at the San Francisco AIDS Foundation said in a statement, “For so long we have only been able to rely on condoms for STI prevention—and we know condoms don’t work for everyone. There is a clear need for additional strategies to reduce STI rates—in San Francisco, and across the US, the number of cases of chlamydia, syphilis, and gonorrhea have been on the rise for many years. It is exciting to have a new tool that we can make available for STI prevention.”
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