There are millions of sexually transmitted infections in the US every year, but new data shows the epidemic may be slowing

(CNN) — Although sexually transmitted infections are still at an epidemic level in the US, scientists at the US Centers for Disease Control and Prevention are expressing cautious optimism about some decreases emerging in the newest data.

Overall, CDC scientists say, there’s evidence that the nation’s STI epidemic may be slowing down, particularly when it comes to gonorrhea and syphilis, but there’s still a long way to go.

“I am encouraged, and it’s been a long time since I felt that way about STIs,” said Dr. Jonathan Mermin, director of the CDC’s National Center for HIV, Viral Hepatitis, STD, and TB Prevention. “However, there were still more than 2.4 million STIs reported in the US in 2023, and the impact of STIs on the health of Americans remains severe.”

There are more than 30 kinds of bacteria, viruses and parasites that people can pass to their partners while having vaginal, anal or oral sex, the World Health Organization says. Some of these infections can also be transmitted from a pregnant person to their child, sometimes with deadly results.

Globally, 1 million curable STIs are passed to a partner or a child every single day, according to WHO. STIs can also cause health problems beyond initial symptoms; some may lead to reproductive problems and even organ damage if left untreated.

A CDC report, released Tuesday, tracks three nationally notifiable STIs – chlamydia, gonorrhea and syphilis – and finds that over a million more cases were reported annually in the US in 2023 than 20 years prior.

Chlamydia

Chlamydia, a bacterial infection, was the most common STI in the new report.

The number of chlamydia cases reported in the US in 2023 – more than 1.64 million – was about the same as the year before. There was a slight increase in the rate of cases among men and a slight decrease among women.

Adolescents and young adults consistently make up more than half of chlamydia cases.

One of the biggest challenges with chlamydia is that there are often no symptoms, or an infection may have minor signs that are shared with other diseases, like a burning sensation when urinating or abnormal discharge. However, without treatment, chlamydia can cause problems that make it difficult to get pregnant later.

A person with chlamydia can be treated with antibiotics, and condoms can prevent infections.

The CDC recommends that sexually active gay and bisexual men get tested for chlamydia every year. The agency also recommends annual testing for women who are sexually active and younger than 25 or who are are older than 25 and have risk factors like multiple sex partners.

Gonorrhea

There were 601,319 cases of the bacterial infection gonorrhea reported in 2023, the second straight year of declines.

The rate of gonorrhea cases decreased 7.7% from 2022 to 2023 and 9.2% from 2021 to 2022. The decreases were seen across the board, for all demographics.

As with chlamydia, gonorrhea may not cause symptoms, but an untreated infection may lead to fertility problems. It can be prevented by using condoms and treated with antibiotics.

Doctors recommend annual testing for all sexually active women under the age of 25 or those older with multiple sex partners, and the CDC suggests that sexually active gay and bisexual men get tested every year.

Syphilis

Syphilis, a bacterial infection that can damage the brain, nerves, heart and eyes if left untreated, has been a growing challenge for health care providers in the United States. The country has seen double-digit increases in case rates over the past few years, but in 2023, rates increased only slightly, at 1%.

The total number of syphilis cases reported in 2023 was 209,253, the highest number since 1950. The new report notes that there were significant declines in people in the first two stages of the disease, which are more infectious than later stages.

Syphilis spreads when a person comes into contact with a syphilis sore, and not all sores may be covered by a condom, so condoms don’t prevent all cases.

The CDC recommends that people who are sexually active and who identify as a gay or bisexual man get tested regularly. The agency also suggests testing for people who have HIV, people taking PrEP to prevent HIV, those living in a community with high rates of syphilis or those who have a partner who has tested positive for syphilis.

Pregnant people can pass syphilis to their fetus, for whom an infection can be highly dangerous, possibly leading to stillbirth, preterm birth or even newborn death. All pregnant people should also get tested on their first prenatal visit. If they have an infection, antibiotics can prevent the spread of the disease to the fetus.

The number of congenital syphilis cases for 2023 was the highest since 1992, with 3,882 cases reported, including 279 related stillbirths and neonatal/infant deaths. However, the rate of congenital cases shows signs of slowing, with only a 3% increase between 2022 and 2023. By comparison, some previous years saw increases of up to 30%, the CDC said.

What’s behind the trends?

The researchers behind the new report say they can’t explain exactly why so many people have STIs, although the epidemic in the US follows a global trend.

The CDC’s Mermin believes that there are several factors driving STI trends, including a concerted effort among leaders in the public health community to diagnose and treat diseases early on, to help control the spread. He also says the increasing number of people who are going on PrEP to prevent HIV may be driving down the numbers because they get regularly tested for STIs.

Additionally, Mermin noted an “unprecedented” temporary infusion of funding for disease intervention specialists at public health departments from the Biden administration. There is no clear indication that such funding would continue or increase under the second Trump administration, and funding varies at the local and state levels.

“It’s important that we put our resources where our epidemics are, and STI prevention is a component of public health,” Mermin said.

The numbers in the report reflect what Dr. Philip Chan is seeing at his own clinic, Open Door Health, the only publicly funded STI clinic in Rhode Island. Although the improvement in rates of disease is encouraging, he said, good numbers from one year don’t mean the epidemic is over.

Chan, an associate professor of behavioral and social sciences and associate professor of medicine at Brown University, said he believes that increased testing and treatment are disrupting STI transmissions in the community. He also points to other positive trends like a decline in the number of high schoolers who have four or more sex partners and a 10% decrease in the number of high schoolers who say they’re having sex at all.

“That’s good news, and we know that regardless of your views on sex, that the later sexual debut is, is generally associated with better health outcomes,” said Chan, who was not involved with the new report.

For this positive trend among STIs to continue, he said, what would help most is something that would help Americans’ health in general.

“I think the biggest thing that we could do as we talk about STIs is just improve general access to primary care and health in general,” Chan said. “Access to care is really probably the most important thing.”

CNN’s Deidre McPhillips contributed to this report.

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