Sexually transmitted infections (STIs) are more common than many people realize. The World Health Organization estimates that more than 374 million new STIs occur each year worldwide, and chlamydia alone accounts for more than 1/4 of those cases among adults ages 15 to 49.

It's so prevalent, in fact, "that chlamydia is the most common bacterial sexually transmitted infection in the United States," says Dr. Orchideh Alexander, an obstetrics and gynecology physician with Atlantic Health in New Jersey. In 2023 alone, more than 1.6 million new cases were reported, per the U.S. Centers for Disease Control and Prevention.

Because chlamydia often causes no symptoms, these numbers likely underestimate its true prevalence. But even these statistics highlight just how widespread – and silent – the infection really is.

What is chlamydia?

Chlamydia refers to a group of bacteria that includes species such as Chlamydia trachomatis, Chlamydia pneumoniae and Chlamydia psittaci. "When in reference to sexually transmitted infections," explains Dr. Melissa Suarez, an obstetrics and gynecology physician with Inspira Health in New Jersey, it is specifically Chlamydia trachomatis that causes infection in humans.

"About 80% of people with chlamydia don't develop symptoms," notes Dr. Michael Shen, an internal medicine physician at NYC Health + Hospitals/Brooklyn. But when symptoms do occur, they typically appear within one to several weeks after exposure.

These may include pain or burning during urination, abnormal discharge such as mucus or pus from the penis or vagina, pain at the cervix ("the deepest part of the vagina that leads to the uterus," explains Shen), testicular or rectal pain and in some cases, infection of the uterus that causes lower abdominal pain and fever.

Because the infection is so frequently asymptomatic, routine testing is essential. Diagnosis usually involves a laboratory test that detects the bacterium’s genetic material from either DNA or RNA. These tests can be performed on urine samples or swabs taken from the vagina, cervix, urethra, rectum or throat.

Left untreated, chlamydia can cause serious complications, particularly in women. These include pelvic inflammatory disease, chronic pelvic pain, ectopic pregnancy and even infertility.

How do you get chlamydia?

The bacteria that cause chlamydia spread through direct contact, "most commonly during sexual interactions including, but not limited to, vaginal, anal and oral sex," says Suarez. Less common but still important routes of transmission include mother-to-child spread during childbirth, which can cause eye infections or pneumonia in newborns.

Because of how chlamydia is spread, it can infect extragenital sites such as the rectum and throat, especially if these areas are exposed during sexual activity.

Certain groups face higher risk of transmitting or getting chlamydia, including adolescents and young adults, people with multiple or new sexual partners, those who do not use condoms consistently and individuals whose partners have STIs.

How is chlamydia treated? Is chlamydia curable?

Chlamydia is treatable and curable with antibiotics that are "usually taken for about a week," says Shen. With proper treatment, most infections clear within one to two weeks.

It is important to complete the full course of the antibiotic, and recent sexual partners should also be notified and treated to prevent reinfection or further spread, says Alexander. People undergoing a course of treatment should abstain from sexual activity until they and their partners have finished medication and all symptoms have resolved. "Individuals are re-tested between four weeks to three months later to confirm that reinfection has not occurred," says Suarez.

While antibiotics eliminate the infection itself, supportive measures can ease discomfort until the medication takes effect. Over-the-counter pain relievers, warm compresses or heating pads for abdominal or pelvic pain, staying hydrated and getting adequate rest can help manage symptoms in the short term.

Ultimately, chlamydia is one of the most common STIs, but it is also one of the easiest to diagnose and cure. "You can decrease your risk," says Shen, "by using condoms consistently, having a sexual safety conversation with new partners and doing regular STI testing with your doctor."

This article originally appeared on USA TODAY: The most common STI may not be the one you expect

Reporting by Daryl Austin, USA TODAY / USA TODAY

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