Human papillomavirus, or HPV, is the most common sexually transmitted infection in the United States and worldwide. An estimated 42 million Americans were living with a disease-associated HPV infection in 2018, with roughly 13 million new infections occurring that year alone. If you narrow the question to bacterial STIs, chlamydia takes the top spot, with about 1.5 million reported cases in the U.S. in 2024.
HPV by the Numbers
HPV is so widespread that most sexually active people will contract at least one type at some point. Of the 42 million Americans infected, about 23.4 million were male and 19.2 million were female. New infections split similarly: 6.9 million in males and 6.1 million in females per year. Many of these infections clear on their own without symptoms, which is exactly why HPV spreads so easily. People often have no idea they’re carrying the virus.
The real danger of HPV lies in the strains that don’t clear. High-risk HPV types cause roughly 39,300 cancers per year in the United States. The largest share is oropharyngeal cancer (cancers of the throat and back of the tongue), accounting for about 16,000 cases annually. Cervical cancer follows with approximately 11,100 cases, and anal cancer adds another 7,600. HPV also causes cancers of the vulva, vagina, and penis in smaller numbers.
HPV Vaccination Has Changed the Picture
The HPV vaccine, first recommended for girls in 2006, has had a dramatic effect. Within 12 years of its introduction, infections with the four HPV types it targets dropped 88% among 14- to 19-year-old females and 81% among 20- to 24-year-old females. Genital warts, one of HPV’s most visible effects, fell 61% among 15- to 19-year-old females between 2006 and 2014. Cervical precancer rates among screened women aged 18 to 20 dropped by half over a similar period.
The vaccine is now recommended for both boys and girls, ideally starting at age 11 or 12, though it can be given as early as 9 and as late as 26 for most people. Some adults up to age 45 may benefit depending on their risk factors. There is no routine HPV screening test for men; for women, cervical cancer screening with a Pap test is recommended every three years starting at age 21, with HPV co-testing an option starting at 30.
Chlamydia: The Most Common Bacterial STI
Chlamydia consistently ranks as the most frequently reported bacterial STI. In 2024, about 1.5 million cases were reported to the CDC, though the actual number of infections is much higher since many go undiagnosed. Chlamydia often causes no symptoms at all, particularly in women. When symptoms do appear, they typically include abnormal discharge, burning during urination, or pelvic pain.
Left untreated, chlamydia can cause serious complications. In women, the infection can spread to the uterus and fallopian tubes, leading to pelvic inflammatory disease, chronic pain, and infertility. In men, it can cause painful swelling in the tube that carries sperm. The good news is that chlamydia is easily cured with antibiotics, and screening is straightforward with a urine test or swab.
Screening guidelines recommend annual chlamydia testing for all sexually active women under 25 and for older women with risk factors like a new partner, multiple partners, or a partner who has an STI. Men who have sex with men should be tested at least annually, and more frequently if they’re on PrEP or have multiple partners.
Where Gonorrhea and Syphilis Stand
Gonorrhea was the second most reported bacterial STI in 2024, with about 543,000 cases, a 10% decline from the prior year. Like chlamydia, it often produces no symptoms but can cause painful urination, discharge, and fertility problems if untreated. A growing concern with gonorrhea is antibiotic resistance, which limits treatment options.
Syphilis cases have been declining recently, with primary and secondary syphilis (the most infectious stages) dropping 22% between 2023 and 2024 to about 41,500 cases. The alarming exception is congenital syphilis, which occurs when a pregnant person passes the infection to their baby. Nearly 4,000 cases of congenital syphilis were reported in 2024, a figure that is 700% higher than a decade ago. Congenital syphilis can cause stillbirth, bone deformities, and developmental problems.
Young Adults Carry the Heaviest Burden
People aged 15 to 24 make up about a quarter of the sexually active population but account for half of all new STI cases each year. Several factors drive this disparity. Younger people are more likely to have new or multiple partners, less likely to use barrier protection consistently, and less likely to get screened. Biology plays a role too: the cervix in younger women is more susceptible to infection.
Globally, the numbers are staggering. The World Health Organization estimates that more than 1 million new cases of chlamydia, gonorrhea, syphilis, or trichomoniasis occur every day among adults aged 15 to 49. Trichomoniasis, caused by a parasite rather than bacteria or a virus, is actually the most common curable STI worldwide, though it receives far less attention than chlamydia or gonorrhea.
Overall Trends Are Improving, but Slowly
The combined total of reported chlamydia, gonorrhea, and syphilis cases in the U.S. dropped for the third consecutive year in 2024, falling 9% from 2023. That still adds up to more than 2.2 million reported cases, and the overall number remains 13% higher than it was a decade ago. The decline is encouraging, but the sheer volume of infections, combined with the rise in congenital syphilis and growing antibiotic resistance in gonorrhea, means the problem is far from solved.
Regular screening remains the single most effective way to catch these infections early, since so many produce no symptoms. If you’re sexually active and under 25, annual screening for chlamydia and gonorrhea is a baseline recommendation. For HPV, vaccination before exposure to the virus is far more effective than any screening test at preventing long-term harm.