Sexually transmitted infections are extremely common. In the United States alone, more than 2.2 million cases of chlamydia, gonorrhea, and syphilis were reported in 2024. And those are just the bacterial infections that get reported. When you factor in viral infections like HPV and herpes, the actual number of people living with an STI at any given time is far higher.
The Numbers in the U.S.
The three most commonly reported bacterial STIs in 2024 broke down like this: chlamydia led with roughly 1.5 million cases, followed by gonorrhea at about 543,000, and syphilis at around 190,000. Those combined totals actually declined 9% from the year before, marking a third consecutive year of decreases. Still, 2.2 million reported cases in a single year means these infections remain widespread.
These numbers also undercount the real picture significantly. Many people with bacterial STIs never get tested, so their infections are never reported. And viral STIs like HPV, herpes, and HIV aren’t captured in these totals at all. HPV alone infects roughly 42.5% of American adults between the ages of 18 and 59 at any given time, with rates slightly higher in men (45%) than women (40%). That means nearly half of all sexually active adults are carrying at least one strain of HPV right now, most without knowing it.
Who Gets STIs Most Often
Young people bear a disproportionate share of the burden. People ages 15 to 24 account for half of all new STI cases despite representing only about 25% of the sexually active population. This isn’t because younger people are inherently more reckless. It reflects a combination of biological factors (the cervix is more susceptible to infection in younger women), less consistent condom use, and lower rates of routine screening.
Risk also varies by the type of sexual contact. Oral and rectal infections tend to fly under the radar more than genital ones, which plays into the next major issue with STIs: most of them don’t cause obvious symptoms.
Most Infections Cause No Symptoms
One of the reasons STIs spread so easily is that the majority of infected people feel perfectly fine. Chlamydia and gonorrhea are the clearest examples. Oral and rectal chlamydia and gonorrhea infections are asymptomatic roughly 91 to 92% of the time. Even genital infections show no symptoms in about 25% of cases. Syphilis follows a similar pattern, with about 61% of positive screens turning up in people who had no idea they were infected.
This is why screening matters so much. If you’re sexually active and waiting for symptoms to appear before getting tested, you could be carrying and transmitting an infection for months or even years without realizing it. Chlamydia, left untreated, can cause pelvic inflammatory disease in women and fertility problems in both sexes. Syphilis can progress through increasingly serious stages if it’s never caught.
Bacterial vs. Viral: A Key Difference
Bacterial STIs like chlamydia, gonorrhea, and syphilis are curable with antibiotics. Getting tested and treated early resolves the infection completely in most cases. That’s the good news, and it’s a strong reason to get routine screening even if you feel fine.
Viral STIs work differently. HPV, herpes, and HIV can’t be cured, though they can be managed. Most HPV infections clear on their own within a year or two, and vaccination prevents the strains most likely to cause cancer or genital warts. Herpes is lifelong but manageable with antiviral medication that reduces outbreaks and lowers transmission risk. HIV, once a death sentence, is now a chronic condition that people live with for decades on modern treatment.
The Global Picture
STIs aren’t just an American problem. The World Health Organization estimates that more than 1 million new cases of just four curable STIs (chlamydia, gonorrhea, syphilis, and trichomoniasis) occur every single day worldwide among adults aged 15 to 49. That’s over 365 million new curable infections per year globally, not counting viral STIs.
What This Means for You
If you’re sexually active, the odds that you’ll encounter an STI at some point are high. Nearly half of adults already carry HPV, millions of new bacterial infections occur each year, and most infected people don’t show symptoms. None of this is cause for panic. It does mean that regular testing is just a normal part of taking care of your sexual health, not something reserved for people who think something is wrong. Most STI tests are simple blood draws or urine samples, and the bacterial infections that make up the bulk of reported cases are straightforward to treat once identified.