STDs (also called STIs) are extremely common. In the United States alone, more than 2.2 million cases of the three nationally reported infections (chlamydia, gonorrhea, and syphilis) were documented in 2024. That translates to roughly 661 cases per 100,000 people. But those three infections are only part of the picture. When you factor in viral infections like HPV, herpes, and HIV, plus underreported infections like trichomoniasis, the true scope is far larger.
HPV: The Most Common STD
Human papillomavirus is so widespread that about 85% of people will get an HPV infection at some point in their lifetime. Most of these infections clear on their own within a year or two without causing symptoms, which is why many people never realize they had one. A small percentage of HPV infections persist and can lead to genital warts or, over many years, cervical and other cancers. Vaccination has significantly reduced infection rates among younger age groups, but HPV remains the single most common sexually transmitted infection worldwide.
Herpes Prevalence by Age and Sex
Genital herpes caused by HSV-2 affects roughly 12% of Americans aged 14 to 49. That’s about one in eight people in that age range. Women are nearly twice as likely to carry the virus as men: 15.9% compared to 8.2%. Prevalence climbs steadily with age, from less than 1% among teenagers to over 21% among people in their 40s. This makes sense because herpes is a lifelong infection, so the longer someone has been sexually active, the more likely they are to have encountered it.
HSV-1, traditionally associated with oral cold sores, is even more common at 47.8% of the same age group. HSV-1 can also cause genital herpes through oral sex, blurring the line between the two types.
Chlamydia, Gonorrhea, and Syphilis
These three bacterial infections make up the bulk of reported STD cases in the U.S. In 2024, the combined total was about 2.25 million cases, though that number actually reflects a 9% decline from the year before. Chlamydia is by far the most frequently reported, followed by gonorrhea. Both have been trending downward in recent years, with chlamydia cases dropping 8% and gonorrhea cases dropping 10% from 2023 to 2024.
Syphilis tells a different story. While primary and secondary syphilis (the most infectious stages) fell 22% in the most recent year, the disease had surged dramatically in the years before that. Congenital syphilis, which passes from a pregnant person to their baby, remains a serious concern. Nearly 4,000 cases were reported in 2024, and the rate of maternal syphilis increased 222% between 2016 and 2022. In 2023, the U.S. recorded the highest number of congenital syphilis cases since 1992.
Trichomoniasis: Widely Underreported
Trichomoniasis is a parasitic infection that rarely shows up in official STD statistics because it isn’t a nationally notifiable disease. The CDC estimates there were more than 2 million trichomoniasis infections in the U.S. in 2018. That single infection nearly matches the combined total of chlamydia, gonorrhea, and syphilis cases reported in a given year. It is easily treated with antibiotics, but because most people with trichomoniasis have no symptoms, it often goes undiagnosed and continues to spread.
HIV in the United States
Approximately 1.2 million people aged 13 and older were living with HIV in the U.S. at the end of 2022. About 31,800 people acquired HIV that year. While these numbers are far smaller than those for chlamydia or HPV, HIV remains significant because it is a lifelong infection requiring ongoing treatment. Modern antiretroviral therapy allows most people with HIV to live long, healthy lives and to reduce their viral load to undetectable levels, which prevents transmission to partners.
Young Adults Carry a Disproportionate Share
People aged 15 to 24 accounted for 53% of all new STI cases in 2020, despite making up a much smaller share of the total 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. Biology plays a role too: the cervix in younger women is more susceptible to certain infections like chlamydia.
Why Official Numbers Undercount the Real Total
The 2.2 million reported cases in the U.S. represent only the infections that were actually diagnosed, tested for, and reported to public health authorities. The majority of STIs either cause no symptoms at all or produce symptoms mild enough that people don’t seek care. Chlamydia, for example, is asymptomatic in roughly 70% of women and 50% of men who have it. Gonorrhea, trichomoniasis, and HPV can all be similarly silent. This means the true number of infections circulating at any given time is substantially higher than what surveillance data capture.
The Global Picture
Worldwide, the World Health Organization estimated 374 million new infections in 2020 across four curable STIs alone: 156 million cases of trichomoniasis, 129 million cases of chlamydia, 82 million cases of gonorrhea, and 7.1 million cases of syphilis. That works out to more than one million new curable STI infections per day globally. These numbers exclude viral infections like HPV, herpes, and HIV, which would push the total significantly higher.
Taken together, the data paint a clear picture: STDs are not rare or unusual. They are among the most common infectious diseases in the world, affecting people across every age group, income level, and background. Regular screening is the most reliable way to catch infections early, since waiting for symptoms means many cases will be missed entirely.