Sudden syphilis retreat in gay men is most likely tied to preventive antibiotic use

The public health workforce tasked with fighting what has been a long-losing battle against sexually-transmitted infections now finds itself confronted with a new, unfamiliar outlook: hope.

After having surged to record levels practically every year this century, overall diagnoses of the three top bacterial STIs have crested since the Covid pandemic. From 2022 to 2023, total diagnoses decreased by 2%, to 2.46 million new cases, according to a Centers for Disease Control and Prevention STI surveillance report published Tuesday.

And importantly, diagnoses of primary and secondary syphilis — the most infectious stages of the infection — dropped 10% last year, to 53,000 cases.

The decline was driven by a 13% drop in such syphilis diagnoses among gay and bisexual men, who are about 2% of the adult population but have historically accounted for nearly half of such cases.

STIs also spread disproportionately among young people and racial minorities. Just under half of the top three bacterial STIs were diagnosed among 15 to 24 year olds last year. Nearly one-third of cases were among Blacks, who are 13% of the population.

Gonorrhea declined by 7%, to 601,300 cases, last year; that followed a 9% decline the previous year. Among all stages of syphilis, cases increased 1%, to 209,250 diagnoses. Chlamydia remained stable from 2021 to 2023, at about 1.65 million cases.

“I think we’re at an inflection point, and it’s important that we push forward and take advantage of innovations and investment of STI prevention going forward,” said Dr. Laura Bachmann, chief medical officer of the CDC’s STI prevention division.

The half-dozen other infectious disease experts who spoke with NBC News about the CDC report said they believed the sudden turnaround in syphilis diagnoses among gay and bisexual men was likely to be an early signal of such men’s eager adoption of a new, proven protocol in which the oral antibiotic doxycycline is used for STI prevention.

“That is huge cause for celebration. And I am a little surprised we see that trend at the national level already,” said Dr. Julie Dombrowski, a professor of medicine at the University of Washington. 

Referring to a recent decline in syphilis among men in Seattle, she added, “We definitely have seen it at the local level.”

Some experts expressed hope that doxycycline use among gay and bisexual men would have a positive spillover effect in women of childbearing age.

Syphilis poses the greatest threat to newborns, among whom it can cause severe congenital defects and death. Whereas cases of the STI in newborns increased by 30% annually in recent years — greatly alarming public health experts — the upward trend has decelerated. Such a promising shift was apparently driven in part by nationwide efforts to increase testing among pregnant women.  

In another hopeful development, a shortage that began in early 2023 of the only recommended treatment for syphilis among pregnant women, Pfizer’s Bicillin-LA, has abated.

In recent years, a trio of randomized controlled trials have shown that instructing gay and bisexual men and transgender women to take one 200-milligram tablet of doxycycline within 72 hours of condomless sex lowers cases of chlamydia and syphilis among them by more than 70% and of gonorrhea by about 50%.

The protocol is known as doxyPEP, which is short for doxycycline post-exposure prophylaxis.

San Francisco’s Public Health Department was the first to recommend doxyPEP for gay and bisexual men and trans women, in October 2022. The CDC followed suit in June. So have health departments in other large cities, such as Chicago and New York, where LGBTQ community health centers have begun offering doxycycline to patients. 

A study of doxyPEP among cisgender women in Africa failed to show efficacy. There is, however, an ongoing trial in U.S. women. 

Thanks to penicillin, the nation made steady progress in fighting syphilis after World War II. By the mid-1990s, public health leaders were entertaining the possibility that the STI could be eliminated.

But the approval of effective HIV treatment in 1996 reduced the public’s fear of AIDS. That helped trigger a long decline in condom use among gay and bisexual men in particular. The subsequent approval of the HIV-prevention pill — called pre-exposure prophylaxis, or PrEP — in 2012 only hastened the decline. 

Bacterial STIs soared accordingly. 

DoxyPEP offers a promising form of harm reduction. It’s cheap and well-tolerated, and it can easily be folded into many gay and bisexual men’s routines for receiving prescriptions to treat or prevent HIV.  

Early analyses suggest doxyPEP is a sleeper hit in that population. 

A study published this month in the journal Sexually Transmitted Diseases found that San Francisco’s guidance on the preventive tool was tied to a decline in STIs among local men. A study published in next month’s edition of the journal found that among about 900 gay and bisexual men recruited for a survey through hook-up apps, half had heard of doxyPEP and nearly all expressed interest. 

A spokesperson for the PrEP-focused telehealth service MISTR told NBC News that since the company started offering doxyPEP in April, three-quarters of users who have filled PrEP prescriptions since then have also requested and received doxycycline. (The representative declined to provide the number of users this entailed but said that that MISTR serves “over 450,000 patients in all 50 states, D.C. and Puerto Rico.”) Since then, the overall quarterly STI positivity rate among MISTR users has plummeted from 12% to 6%.

In November 2023, the Food and Drug Administration approved the first at-home tests for gonorrhea and chlamydia, which public health experts hope might also help combat the spread of STIs. 

And in July, researchers presented findings at a global HIV conference in Munich of studies in which gay and bisexual men in Canada and female sex workers in Japan were instructed to take 100 milligrams of doxycycline daily. The protocol, called doxyPrEP, demonstrated generally comparable efficacy at preventing STIs compared with doxyPEP studies among gay men.

Research is ongoing to address concerns that increased use of doxycycline to prevent STIs might help fuel the burgeoning drug-resistant pathogen crisis. Thus far, researchers have found reassuring signs. 

STI-prevention experts are also concerned that, as with HIV PrEP, doxyPEP will prove disproportionately popular among whites and thus will only widen racial disparities in STI transmission. Research is underway to analyze trends in doxyPEP’s use that could help focus promotion of the intervention where the need is greatest.

Public health experts have attributed this century’s surge in STIs, at least in part, to a steady defunding of state and local public-health clinics.

Dr. Jeffrey Klausner, an infectious disease expert at the University of Southern California who led the first study to demonstrate doxyPEP’s efficacy, called for renewed spending on STI-related care. 

“If Trump is going to make IVF — in vitro fertilization — free,” Klausner said of the president-elect’s emphatic campaign pledge, “he should make STI testing and treatment free.”

This story first appeared on NBCNews.com. More from NBC News:

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