Chlamydia is the most commonly reported bacterial sexually transmitted infection in the world. An estimated 128.5 million new cases occur globally each year among adults aged 15 to 49, according to World Health Organization data from 2020. In the United States alone, over 1.5 million cases were reported in 2024, and the true number of infections is almost certainly higher because most people with chlamydia never know they have it.
Global Numbers at a Glance
Worldwide, roughly 4% of women and 2.5% of men between the ages of 15 and 49 are living with a chlamydia infection at any given time. That translates to tens of millions of active infections on top of the 128.5 million new ones each year. The gap between men and women in these numbers partly reflects biology (the infection is more easily transmitted to women) and partly reflects screening patterns, since women are tested far more often.
How Many Cases Are Reported in the U.S.
Provisional CDC surveillance data for 2024 counted 1,515,985 reported chlamydia cases across the United States, a rate of about 446 per 100,000 people. Women accounted for nearly two-thirds of those reports: 943,890 cases in women (549.5 per 100,000) compared to 564,489 in men (335.3 per 100,000).
Those numbers represent only confirmed, lab-reported cases. Because 75% of women and 50% of men with chlamydia develop no symptoms at all, many infections are never tested for and never counted. CDC researchers have used national health surveys and mathematical modeling to estimate the actual burden, and the true number of annual infections in the U.S. is believed to be substantially higher than what surveillance captures.
Who Gets Chlamydia Most Often
Young adults bear a disproportionate share of the burden. The U.S. Preventive Services Task Force recommends annual chlamydia screening for all sexually active women aged 24 and younger precisely because rates in this group are so high. For women 25 and older, screening is recommended if risk factors are present: a new sexual partner, multiple partners, a partner who has other concurrent partners, inconsistent condom use outside a monogamous relationship, or a history of a previous STI.
For men, there is no universal screening recommendation. The evidence on whether routine screening in men reduces transmission or complications at a population level is still considered insufficient by the task force. In practice, this means men are typically tested only when they have symptoms or are identified as a sexual contact of someone who tested positive, which contributes to lower reported case counts in men.
Why So Many Cases Go Undetected
Chlamydia’s defining feature, from a public health perspective, is how quietly it spreads. Three out of four women and half of men who are infected experience no symptoms whatsoever. No pain, no discharge, no obvious sign that anything is wrong. This makes it easy to carry and transmit the infection for weeks or months without knowing.
When symptoms do appear, they typically show up one to three weeks after exposure. Women may notice unusual vaginal discharge or bleeding between periods. Men may experience a burning sensation during urination or discharge from the penis. But because these symptoms can be mild and easy to dismiss, even symptomatic cases often go untested.
Reinfection Is Common
Chlamydia is curable with antibiotics, and treatment success rates are high. But getting treated once does not protect you from catching it again. Reinfection rates among adolescents range from 7% to 38% across various studies, with one clinical analysis finding that 22% of young patients who were retested after treatment had a second positive result. This is why the CDC recommends retesting about three months after completing treatment, regardless of whether your partner was also treated.
What Happens if Chlamydia Goes Untreated
Left untreated, chlamydia can cause serious reproductive damage, particularly in women. About 10% to 15% of women with untreated chlamydia develop pelvic inflammatory disease, an infection of the uterus, fallopian tubes, or ovaries that can lead to chronic pelvic pain, ectopic pregnancy, and infertility. The risk compounds with repeated infections, meaning reinfection is not just an inconvenience but a genuine threat to long-term fertility.
In men, untreated chlamydia can cause epididymitis, a painful inflammation of the tube that carries sperm from the testicle. While this rarely leads to infertility in men, it can be quite painful and may require a longer course of treatment. In both sexes, having an active chlamydia infection also increases susceptibility to HIV if exposed.
Why the Numbers Keep Climbing
Rising case counts over the past decade don’t necessarily mean more people are getting infected. Part of the increase reflects better and more widespread testing. Newer tests that use urine samples or self-collected swabs have made screening easier and more accessible, catching infections that previously would have gone undiagnosed. At the same time, some public health experts believe that declining condom use, particularly among younger adults, is driving a genuine increase in transmission. Both factors are likely at play, and separating them in the data is difficult.
What is clear is that chlamydia remains deeply undertreated relative to its scale. With over a hundred million new infections a year worldwide and the majority producing no symptoms, the gap between how many people actually have chlamydia and how many know about it remains one of the largest challenges in STI prevention.