After decades of unrelenting increases, rates of sexually transmitted infections in the United States are showing hints of a downturn.
Diagnoses of gonorrhea dipped in nearly all age groups last year, compared with 2022, and new cases of syphilis and chlamydia remained about the same, according to data released on Tuesday by the Centers for Disease Control and Prevention.
The results are not yet cause for celebration.
Overall, more than 2.4 million new S.T.I.s were diagnosed last year, about a million more than the figure 20 years ago. Nearly 4,000 babies were diagnosed with congenital syphilis last year, and 279 of them were stillborn or died soon after.
Still, experts said they were cautiously optimistic that a resurgent tide of infections was beginning to turn.
“It’s been a long time since I have felt that way about the S.T.I. epidemic,” said Dr. Jonathan Mermin, director of the National Center for H.I.V., Viral Hepatitis, S.T.D. and TB Prevention at the C.D.C.
The drop in cases may be the result of a variety of factors: an infusion of funds into health departments during the Covid-19 pandemic, changes in sexual behavior among gay and bisexual men because of the mpox outbreak in 2022 and the recent availability of the antibiotic doxycycline to forestall S.T.I.s after unprotected sexual encounters.
“Combined, all of those different activities could have led to some of the decreases that we’re seeing,” Dr. Mermin said.
Diagnoses of gonorrhea dropped for the second consecutive year, indicating that a dip observed in 2022 was not a one-off. The rate of gonorrhea cases per 100,000 people decreased by 9.2 percent from 2021 to 2022, and by 7.7 percent last year.
Syphilis was nearly eliminated in the United States about 20 years ago, but infections have soared in recent years. More than 207,000 cases were diagnosed in 2022, an increase of 17 percent over the figure in 2021.
The trends in 2023 were much less dire. Cases of syphilis overall increased by just 1 percent. Congenital syphilis rose by 3 percent, a much smaller bump compared with the 32 percent increase between 2020 and 2021.
Syphilis during pregnancy can lead to miscarriage and stillbirth, and infants who survive may become blind or deaf or have severe developmental delays. A C.D.C. report last year concluded that nearly 90 percent of new cases in 2022 could have been prevented with timely testing and treatment.
A single shot of penicillin during pregnancy can prevent death or disability from congenital syphilis, said Dr. Ina Park, an S.T.I. expert at the University of California, San Francisco.
“There is absolutely no reason a baby should be dying of syphilis in 2024,” she said.
Other types of syphilis decreased significantly. Primary and secondary syphilis, the phases of infection at which people are most contagious, fell by 10 percent. And among gay and bisexual men, diagnoses dropped by 13 percent, the first decrease in more than 15 years.
The trend in cases differed by age groups and by region. Nearly half of new S.T.I.s in 2023 were in adolescents and young adults ages 15 to 24. Native American and Alaska Native people and Black Americans were disproportionately affected, and infections were more common in the South than elsewhere in the country.
Not all Southern schools include sex education in their curriculums. If they do, they may teach only abstinence, said Dr. Thomas Dobbs, dean of the University of Mississippi’s John D. Bower School of Population Health.
The number of syphilis cases per 100,000 people decreased by less than 5 percent in the South, compared with more than 15 percent in the West and nearly 18 percent in the Northeast, according to the C.D.C.
In Jackson, Miss., patients with S.T.I.s tend to be heterosexual. But the C.D.C. recommends doxycycline to prevent S.T.I.s only in gay and bisexual men and transgender women who have had an S.T.I. in the previous 12 months.
“We don’t really have as many tools out there for the folks that are most affected in Mississippi,” Dr. Dobbs said.
Unlike diseases that can be resolved with a visit to a clinic, S.T.I.s require investigators who can track sexual health partners, and teams of specialists who can treat people where they are.
But the public health systems in Southern states are often poorly funded, and funding — even that from the C.D.C. — for many sexual health programs has been cut steeply.
“It doesn’t really portend well for the future,” Dr. Dobbs said. “I do worry about pockets where we’re going to be behind.”
In many parts of the country, local and state health departments have made a concerted effort to step up testing for S.T.I.s in clinics, emergency rooms, jails and other correctional settings, and places — including barbershops and churches — where people gather.
Some departments are trying to destigmatize S.T.I.s by addressing the problem openly.
The Biden administration established a task force to combat syphilis. In August, the Food and Drug Administration approved the first at-home tests for syphilis, allowing people to test in the privacy of their homes.
And the Indian Health Service issued recommendations last year to implement universal screening for syphilis infections in individuals ages 13 to 64.
“Never before in my 15-year career have I seen the field so united with a sense of purpose in terms of addressing syphilis and congenital syphilis,” Dr. Park said. “We are starting to see some successes.”
