Sustained Reduction in Sexually Transmitted Infections: Good News but…

“The latest CDC data is a hopeful sign that the nation is making progress on an out-of-control STI epidemic, but we have far more work to do before Americans can feel sufficiently protected.”

Elizabeth Finley, interim executive director of the National Coalition of STD Directors

“If there’s anything that should jump out at you it’s simply this—sexual behavior has declined significantly since the late 1980s.”

Ryan Burge, American political scientist and statistician

While the rates of sexually transmitted infections (STIs) vary from country to country, the World Health Organization estimates there are more than 1 million curable STIs acquired per day worldwide. Six years ago STIs were out of control in the U.S. (See, “Alarming Increase in Sexually Transmitted Diseases: What’s Up?,” Germ Gems, October 27, 2019). So, when the Centers for Disease Control and Prevention (CDC) issued its annual STIs report on September 24, 2025 with data showing that STI rates had fallen for third straight year, I was surprised, if not shocked. (The CDC reports on HIV separately from other STIs; overall HIV case rates have remained stable for the past six years.)

According to the CDC, combined cases of chlamydia, gonorrhea, and syphilis declined 9% from 2023 to 2024, the third straight year of decreases for these STIs. (In contrast, congenital syphilis, that is, mother-to-child transmission, continued to increase over the past decade.) In this week’s Germ Gems post, I provide a brief recap on STIs and discuss the most likely reason for the recent reduction in these infections. In addition, I speculate about the future of STIs in this the “RFK Jr era of public health.”

What are STIs? There are more than 20 types of STIs. The pathogens that cause these infections have evolved a mode of transmission that is both essential to existence and difficult to control. Sexual behaviors that increase the risk of STIs include unprotected vaginal, anal, or oral sex, having multiple partners, and, in the case of HIV, sharing needles. Inconsistent or incorrect condom use and excessive alcohol or drug use also increase the risk of STIs.

More than 30 different pathogens, including bacteria, viruses, and parasites cause STIs. Gonorrhea, chlamydia, syphilis—the “big three STIs” that the CDC closely tracks—are all caused by bacteria and can be treated with antibiotics. Hepatitis B, hepatitis A, genital herpes simplex virus, and human papilloma virus (HPV) are all viral infections, three of which—hepatitis B, hepatitis A, and HPV—can be prevented by vaccines. But the critically important way to reduce STIs is to practice “safe” or “protected” sex, generally by means of a using a condom.

Why are some STIs declining in the United States? Condoms protect against both pregnancy and STIs and were used widely as a birth control method before the oral contraceptive pill became widely available. The introduction of the birth control pill in the 1960s had a major impact on sexual behavior and, indirectly, on rates of STIs. The pill decoupled sex from pregnancy risk, contributing in a major way to the sexual revolution. Because pregnancy prevention was no longer tied to condom use, many couples stopped using condoms. Soon after the wide adoption of the pill, rates of STIs—particularly gonorrhea, chlamydia and syphilis—rose sharply in many countries. The HIV/AIDS epidemic, however, reintroduced condom use for STI prevention and temporarily reversed some of the trends of increased STIs.

But, the reduction in some STIs in the past several years appears to have little, if anything, to do with safe sex practices. Rather, the main driver of reduced cases of STIs appears to be tied primarily to people having less sex.

According to a study by the Institute for Family Studies, the weekly sexual activity of adults in the U.S. dropped from 55% in 1990 to 37% in 2024. (Perdomo, W., “The Great Sex Recession: The number of Americans having sex weekly plummets,” VOZ, September 24, 2025). Drawing upon a 2024 survey of Californians aged 18-30, American scientist and statistician Ryan Burge found the percentage of people reporting no sexual partners in the prior year reached an all time high of 38%.  (Burge, R., “The Data is Clear: People Are Having Less Sex,” Graphs about Religion, March 4, 2024). This trend of less sex was observed in virtually all adult age groups, and it wasn’t associated with any specific religion or marital status. (Married couples reported having sex at about the same rate as during the era of the George W. Bush administration.)

The basis for the reduction in having sex, referred to by some experts as a “sexual recession,” is unclear. Burge, however, opined: “I don’t think it takes too much imagination to conjure the most likely suspect—smartphones. I think we can all admit that sexual behavior is somewhat related to boredom. When you have something to entertain yourself, then sex may not be top of mind.”

Whether Burge is right that availability of technologies, like cell phones, is responsible, at least in part, for Americans having less sex is unknown, but it certainly begs scrutiny by social scientists.

The future of STIs. While the reduction in cases of some STIs in the past three years is certainly good news, the continued rise in congenital syphilis is disconcerting. For the twelfth year in a row, congenital syphilis (infection passed from mother to baby) increased yet again. Nearly 4,000 cases were reported in 2024. A large portion of these cases come from mothers who either did not receive prenatal care, or started very late, or were not tested in time. It suggests the United States Public Health Service isn’t doing enough to prevent STIs.

Elizabeth Finley, interim executive director of the National Coalition of STD Directors, surmised, “The continued rise in congenital syphilis is a distressing indication that we are not doing enough to protect pregnant women and newborns from the deadly and preventable consequences of syphilis transmission during pregnancy.” (Stulpin, C.,“STI rates fall for third straight year. CDC data show,” Helio, September 24, 2025). Finley called on the Trump administration—which shut down a CDC laboratory dedicated to tracking STIs earlier this year—to provide necessary resources, information and an effective workforce to ensure states and cities have what they need to win the fight against STIs.

It is doubtful that this will happen. And, given the almost total collapse of Public Health infrastructure that’s occurred under the leadership of Health and Human Services Secretary Robert F. Kennedy, Jr., it doesn’t take much imagination to predict that the recent recession in STIs in the U.S. will soon to turn into an inflation.