About 1 in 5 people in the United States has a sexually transmitted infection at any given time. That estimate, from the CDC, translates to nearly 68 million active infections across the country on any single day. Globally, the numbers are even larger: over 1 million new cases of just four curable STIs occur every day among adults ages 15 to 49, totaling 374 million new infections in 2020 alone.
Those figures surprise most people, largely because the majority of STIs produce no symptoms. The true scope of infection is much wider than what gets reported, tested for, or talked about.
The 1 in 5 Number, Explained
The CDC’s estimate of 1 in 5 Americans counts everyone living with any STI on a given day, including long-lasting viral infections like herpes and HPV alongside bacterial infections like chlamydia. Because viral STIs persist for years or even a lifetime, they make up a large share of that total. If you counted only new infections picked up in a single year, the number would be smaller. But because tens of millions of people are carrying infections they may not even know about, the snapshot on any given day reaches that 20% mark.
This is a prevalence figure, not an annual incidence figure. It reflects how many people are currently infected, not how many got infected recently. The distinction matters because it helps explain why the percentage sounds so high: viral infections accumulate over time in the population.
How Common Each STI Is
Herpes (HSV)
Genital herpes is the single largest driver of that 1-in-5 statistic. Globally, around 846 million people between ages 15 and 49 are living with genital herpes, which means more than 1 in 5 adults in that age range worldwide. About 520 million of those cases are caused by HSV-2, the strain most associated with sexual transmission. Another 376 million involve HSV-1, traditionally known as the “cold sore” virus, which increasingly causes genital infections through oral sex. Most people with herpes never receive a diagnosis because outbreaks can be mild, infrequent, or completely absent.
HPV
Human papillomavirus is the most common STI by raw numbers. Most sexually active people will contract at least one strain of HPV at some point in their lives. The body clears most HPV infections on its own within one to two years, so prevalence at any given moment is lower than lifetime exposure. Still, HPV is so widespread that it’s often considered a near-inevitable part of sexual activity. Vaccination has significantly reduced the strains responsible for cervical cancer and genital warts, but dozens of other strains continue to circulate.
Chlamydia
Chlamydia is the most commonly reported bacterial STI in the United States. In 2024, provisional CDC data recorded about 1.5 million cases, a rate of roughly 446 per 100,000 people. The actual number of infections is almost certainly higher. About 70% of women and 50% of men with chlamydia experience no symptoms at all, so many cases go undiagnosed and unreported. Chlamydia is curable with antibiotics, but untreated infections can cause serious complications including infertility.
Gonorrhea
Gonorrhea accounted for about 543,000 reported cases in the U.S. in 2024, a rate of roughly 160 per 100,000 people. Like chlamydia, gonorrhea often flies under the radar. Up to 40% of infected men and at least 50% of infected women show no symptoms. Gonorrhea is curable, but antibiotic-resistant strains have become a growing concern in recent years.
Syphilis
Syphilis cases in the U.S. totaled about 190,000 in 2024. While syphilis is less common than chlamydia or gonorrhea in absolute numbers, its resurgence has been dramatic. Globally, there were an estimated 8 million new syphilis infections in 2022, along with 700,000 cases of congenital syphilis, where the infection passes from mother to baby during pregnancy. Syphilis is fully curable with treatment but can cause severe organ damage if left untreated for years.
Why Reported Numbers Undercount the Real Total
The cases that show up in surveillance data represent a fraction of all infections. Many STIs produce no noticeable symptoms, which means people never seek testing. Chlamydia is a clear example: when the majority of infected people feel perfectly fine, most infections simply never get counted. Gonorrhea follows the same pattern. Even symptomatic infections go unreported when people avoid testing due to stigma, cost, or lack of access to healthcare.
Viral STIs compound the undercount further. Routine STI panels typically don’t include herpes or HPV testing. Herpes blood tests aren’t recommended for the general population in most screening guidelines, and there’s no approved HPV test for men. So millions of people carrying these infections never appear in any database.
Young Adults Carry a Disproportionate Share
People ages 15 to 24 make up about 25% of the sexually active population in the U.S. but account for roughly half of all new STI cases each year. Several factors converge in this age group: higher rates of new and multiple sexual partners, lower rates of consistent condom use, and biological factors that make younger bodies (particularly the cervix in younger women) more susceptible to certain infections.
This doesn’t mean STIs are a young person’s problem exclusively. Rates among adults over 45 have been climbing steadily, particularly for syphilis and gonorrhea. But the concentration of new infections in the under-25 group is why most screening guidelines target that demographic more aggressively.
Global Numbers at a Glance
Worldwide, the WHO estimates that 374 million new infections of chlamydia, gonorrhea, syphilis, or trichomoniasis occurred among adults ages 15 to 49 in 2020. That works out to over 1 million new curable STI cases per day. These four infections are all treatable with existing antibiotics, yet their sheer volume overwhelms healthcare systems in many parts of the world.
Add in viral STIs, and the global burden grows substantially. The 846 million people living with genital herpes alone represent a massive ongoing reservoir of infection. HIV, while far less common than herpes or HPV, affects approximately 39 million people worldwide and remains concentrated in sub-Saharan Africa and among specific populations elsewhere.
What These Numbers Mean in Practice
If you’re sexually active, the math is straightforward: STIs are common enough that exposure is likely over the course of a lifetime, even with relatively few partners. That reality isn’t a moral statement. It’s an epidemiological one. The high rates of asymptomatic infection mean that your partners may not know their own status, and you may not know yours without testing.
Regular screening is the most practical response to these numbers. The CDC recommends annual chlamydia and gonorrhea screening for all sexually active women under 25, and for older women with risk factors. All adults should be screened for syphilis and HIV at least once. Men who have sex with men benefit from more frequent screening across all STIs. These recommendations exist precisely because so many infections produce no symptoms and would otherwise go undetected until complications develop.