Chlamydia is the most commonly reported STI in the United States, with over 1.5 million cases reported in 2024 alone. If you count infections that aren’t routinely reported to health authorities, HPV (human papillomavirus) is actually more widespread in the general population, but chlamydia dominates the official surveillance numbers by a wide margin. Together, chlamydia, gonorrhea, and syphilis accounted for more than 2.2 million reported infections in 2024.
Chlamydia by the Numbers
In 2024, the CDC recorded 1,515,985 chlamydia cases, making it responsible for roughly two-thirds of all reported STIs that year. Gonorrhea came in second with 543,409 cases, followed by syphilis at 190,242. Those three infections combined totaled about 2.25 million reported cases.
The true number of chlamydia infections is almost certainly higher than what gets reported. The infection frequently produces no symptoms at all: about 75% of women and 50% of men with chlamydia never notice anything wrong. Many cases go undiagnosed simply because people don’t realize they need to be tested.
Why HPV Deserves a Mention
HPV is so common that nearly all sexually active people will contract at least one strain at some point in their lives. However, most HPV infections clear on their own without treatment, and the virus isn’t tracked through the same case-reporting system as chlamydia, gonorrhea, and syphilis. That’s why chlamydia holds the title of most common “reported” STI, while HPV is often called the most common STI overall. The distinction matters because it shapes how each infection is monitored and managed. HPV screening happens through cervical cancer screening programs rather than standard STI testing panels.
Who Gets Chlamydia Most Often
Young people between 15 and 24 account for half of all new STI cases despite representing only about 25% of the sexually active population. Chlamydia follows this pattern closely. Higher rates in younger age groups reflect a combination of biological factors (the cervix is more susceptible to infection in younger women), behavioral patterns, and lower rates of consistent screening.
Because chlamydia so often flies under the radar without symptoms, routine screening is the primary way most cases get caught. The CDC recommends annual chlamydia screening for all sexually active women under 25, with continued screening for those 25 and older who have risk factors like new or multiple partners. Sexually active men who have sex with men are also recommended to screen at least once a year regardless of condom use.
Symptoms and What Happens Without Treatment
When chlamydia does cause symptoms, they typically show up one to three weeks after exposure. Women may notice unusual vaginal discharge, burning during urination, or bleeding between periods. Men often experience discharge from the penis, burning with urination, or pain and swelling in one testicle. Rectal infections can cause pain, discharge, or bleeding regardless of sex.
Left untreated, chlamydia can cause serious complications. In women, the infection can spread to the uterus and fallopian tubes, leading to pelvic inflammatory disease. This can result in chronic pelvic pain, scarring of the reproductive tract, and difficulty getting pregnant. In men, untreated chlamydia occasionally causes infection in the tube that carries sperm, which can lead to pain and, rarely, fertility problems. During pregnancy, untreated chlamydia raises the risk of preterm delivery and can pass to the baby during birth, potentially causing eye infections or pneumonia.
How Chlamydia Is Treated
Chlamydia is curable with antibiotics, typically a week-long course of pills taken twice daily. An alternative is a single-dose treatment, though the week-long regimen is now preferred as first-line therapy. Most people clear the infection completely with proper treatment. You should avoid sexual contact for seven days after starting treatment (or until a single-dose course is complete) to prevent passing the infection to a partner.
Getting treated once doesn’t protect you from getting chlamydia again. Reinfection is common, particularly if a sexual partner wasn’t treated at the same time. The CDC recommends retesting about three months after treatment to make sure you haven’t been reinfected.
Screening Recommendations Worth Knowing
Because so many STIs produce no obvious symptoms, screening guidelines exist for several infections beyond chlamydia:
- Gonorrhea: Same screening schedule as chlamydia. Sexually active women under 25 and men who have sex with men should test at least annually.
- Syphilis: Annual screening recommended for men who have sex with men. Pregnant women are also routinely screened.
- HIV: Everyone between ages 13 and 64 should be tested at least once. Men who have sex with men should test at least annually if their status is unknown or negative.
- HPV/cervical cancer: People with a cervix should begin screening at age 21, with follow-up every three to five years depending on age and test type.
- Hepatitis C: All adults over 18 should be screened at least once.
Most of these tests are simple, requiring only a urine sample or a swab. Many clinics and health departments offer low-cost or free STI testing, and home collection kits are increasingly available for chlamydia and gonorrhea. If you’re sexually active with new or multiple partners, routine screening is the single most effective way to catch infections early, especially the ones you can’t feel.