STDs are extremely common in the United States. Roughly one in five people in the country has a sexually transmitted infection on any given day, and an estimated 20 million new infections occur every year. That makes STIs one of the most widespread categories of infectious disease in the U.S., with a combined healthcare cost approaching $16 billion annually.
The Most Common STIs by the Numbers
Chlamydia is by far the most frequently reported STI. In 2024, over 1.5 million cases were reported to the CDC, translating to about 446 cases per 100,000 people. Gonorrhea came in second with roughly 543,000 reported cases, or about 160 per 100,000. Primary and secondary syphilis, while less common in raw numbers at around 41,500 cases, has been climbing at an alarming pace.
These numbers only reflect cases that were actually diagnosed and reported. Because many bacterial STIs cause no obvious symptoms, particularly oral and rectal infections where over 90% of cases may produce no symptoms at all, the true number of infections is substantially higher than what surveillance data capture.
Viral STIs Affect Millions More
The bacterial infections above get the most attention in annual reports, but viral STIs account for the largest share of the overall burden. HPV (human papillomavirus) is the single most common sexually transmitted infection in the country, with tens of millions of people carrying it at any given time. Most HPV infections clear on their own, but certain strains can lead to genital warts or cancers of the cervix, throat, and other areas.
Genital herpes, caused by HSV-2, is another widespread viral infection that persists for life once acquired. And more than 1.2 million people in the U.S. are currently living with HIV. Unlike bacterial STIs, viral infections generally cannot be cured, only managed, which means they accumulate in the population over time.
Young Adults Carry a Disproportionate Share
People aged 15 to 24 account for half of all new STI cases each year, despite representing only about 25% of the sexually active population. Several factors drive this disparity. Younger people are more likely to have new or multiple sexual partners, less likely to use barrier protection consistently, and less likely to get screened regularly. Biological factors also play a role: the cervix in younger women is more susceptible to infections like chlamydia and gonorrhea.
This concentration among young adults is one reason public health guidelines recommend routine chlamydia screening for all sexually active women under 25, even without symptoms.
Congenital Syphilis Is Surging
One of the most troubling recent trends is the explosion in congenital syphilis, which occurs when a pregnant person passes the infection to their baby. Nearly 4,000 cases were reported in 2024, a figure that is 700% higher than a decade ago. Congenital syphilis can cause stillbirth, severe birth defects, and infant death, and it is almost entirely preventable with early prenatal screening and treatment. The surge reflects both rising syphilis rates overall and gaps in prenatal care access.
Why So Many Cases Go Undetected
A major reason STIs are so widespread is that most infections produce no symptoms, especially in their early stages. Chlamydia and gonorrhea are particularly silent. Genital infections may cause noticeable discharge or pain in some people, but oral and rectal infections are asymptomatic more than 90% of the time. Someone can carry and transmit these infections for weeks or months without knowing.
This is why screening matters more than waiting for symptoms. Many people assume they would “know” if they had an STI, but the biology simply doesn’t work that way for most infections. Regular testing based on risk factors, not symptoms, is the only reliable way to catch and treat infections before they spread or cause complications like pelvic inflammatory disease, infertility, or chronic pain.
The Financial Toll
Beyond the health consequences, STIs carry a significant economic burden. New infections acquired in a single year cost the U.S. healthcare system nearly $16 billion in direct lifetime medical costs. That figure covers only treatment and medical management. It does not include lost productivity, time off work, or the costs of prevention programs, meaning the true economic impact is considerably larger.
Most of that cost comes from viral infections, particularly HIV, which requires lifelong treatment. But the sheer volume of bacterial STIs also adds up quickly, especially when untreated infections progress to complications that require more intensive care.