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.