Sexually transmitted infections are extremely common. Globally, more than 1 million new cases of just four curable STIs (chlamydia, gonorrhea, syphilis, and trichomoniasis) occur every single day, adding up to 374 million new infections per year among adults aged 15 to 49. In the United States alone, more than 2.2 million cases of chlamydia, gonorrhea, and syphilis were reported in 2024. And those numbers only capture infections that get diagnosed and reported. The true burden is significantly higher.
The Most Common STIs by the Numbers
Not all STIs show up equally. Some are so widespread that most sexually active people will encounter them at some point, while others are rarer but rising fast.
HPV is the single most common STI. The CDC puts it bluntly: nearly everyone who isn’t vaccinated will get HPV at some point in their lives. Most HPV infections clear on their own without causing problems, but certain strains can lead to genital warts or cancers of the cervix, throat, and other areas. Vaccination has dramatically reduced infections with the highest-risk strains.
Trichomoniasis, caused by a parasite rather than a bacterium or virus, is another extremely common infection that rarely gets the attention it deserves. In the U.S., about 1.3% of people aged 14 to 59 are infected at any given time. Women are affected at roughly four times the rate of men (2.1% versus 0.5%), partly because the infection persists longer in women and is easier to detect in them.
Chlamydia remains the most frequently reported bacterial STI in the United States and accounts for the largest share of those 2.2 million annual reported cases. Gonorrhea follows behind it. Syphilis, while less common overall, has been surging: globally, there were 8 million new syphilis infections in 2022.
HIV infections in the U.S. have been declining. An estimated 31,800 people acquired HIV in 2022, down 12% from 36,300 in 2018. In communities targeted by federal prevention efforts, new infections dropped by 21% over a similar period. Progress is real, but tens of thousands of new cases per year means HIV remains a significant public health concern.
Young Adults Carry a Disproportionate Burden
People aged 15 to 24 account for half of all new STI cases despite representing only about 25% of the sexually active population. Several factors drive this. Younger people are more likely to have new or multiple partners, less likely to use barrier protection consistently, and less likely to get tested regularly. Biologically, the cervix in younger women is also more susceptible to certain infections like chlamydia.
This concentration of infections in one age group is why routine screening recommendations target young adults more aggressively than older populations.
Most Infections Cause No Symptoms
One of the main reasons STIs spread so effectively is that the majority of infected people feel perfectly fine. Research pooling data across multiple studies found that roughly 61% of chlamydia infections, 53% of gonorrhea infections, and 57% of trichomoniasis infections in women produce no symptoms at all. Men with chlamydia are also frequently asymptomatic, though they tend to notice gonorrhea symptoms more often than women do.
This matters for two reasons. First, people who don’t know they’re infected don’t seek treatment, so they continue passing the infection to partners. Second, untreated chlamydia and gonorrhea can silently damage the reproductive system over months or years, potentially leading to pelvic inflammatory disease, chronic pain, or infertility. By the time symptoms finally appear, if they ever do, the damage may already be done. Regular screening is the only reliable way to catch these infections early.
U.S. Trends: Overall Cases Declining, Syphilis Still Rising
After years of steady increases, the combined total of reported chlamydia, gonorrhea, and syphilis cases in the U.S. dropped 9% from 2023 to 2024, marking a third consecutive year of decline. Over five years, cases are down about 6%. That’s encouraging, though 2.2 million reported cases per year is still an enormous number.
The one glaring exception to this downward trend is syphilis in newborns. Congenital syphilis, which passes from a pregnant person to their baby, increased for the 12th consecutive year in 2024. Cases are up nearly 700% since 2015, when just 495 were reported. Congenital syphilis can cause stillbirth, severe disability, and infant death, and it is almost entirely preventable with a simple blood test and antibiotic treatment during pregnancy. The surge reflects gaps in prenatal care access, particularly in rural areas and underserved communities. Globally, an estimated 700,000 cases of congenital syphilis occurred in 2022.
Gonorrhea Is Getting Harder to Treat
A growing concern beyond raw case counts is that gonorrhea is steadily outsmarting antibiotics. Between 2022 and 2024, resistance to the two primary antibiotics used to treat gonorrhea rose sharply. Resistance to ceftriaxone, the current first-line injectable treatment, jumped from 0.8% to 5%. Resistance to cefixime, an oral alternative, climbed from 1.7% to 11%. The WHO has warned that more countries are reporting these resistant strains.
For now, most gonorrhea infections remain treatable, but the window is narrowing. If resistance continues to climb at this pace, some infections could become extremely difficult to cure with existing drugs. This is one reason public health agencies emphasize prevention and prompt treatment: every untreated infection is another opportunity for resistant bacteria to develop and spread.
Why Reported Numbers Undercount Reality
Every statistic in this article understates the true scope of STIs. Reported case counts only capture infections that were tested for, diagnosed, and then reported to public health authorities. Given that most infections are asymptomatic and many people never get screened, a large share of cases simply go undetected. Trichomoniasis, for instance, is not a nationally reportable condition in the U.S., so it doesn’t appear in CDC surveillance totals at all despite being one of the most common infections. Herpes similarly affects a huge portion of the population but is rarely included in standard STI panels.
The practical takeaway is straightforward. STIs are not rare events that happen to other people. They are a routine part of being sexually active, especially for those with new or multiple partners. Regular screening, even when you feel completely healthy, is the most effective way to protect yourself and your partners from infections you might not know you have.