Chlamydia spreads through sexual contact with an infected person. That includes vaginal, anal, and oral sex. You got it from a sexual partner who had the infection, even if neither of you had any symptoms at the time. This is one of the trickiest things about chlamydia: roughly 75% of women and 50% of men with the infection have no symptoms at all, which means your partner may have genuinely had no idea they were carrying it.
How Chlamydia Spreads During Sex
The bacteria that causes chlamydia, called Chlamydia trachomatis, passes from one person to another through infected genital fluids. It can infect the cervix, urethra, rectum, and throat. Any sexual contact that involves these areas can transmit the infection, with or without ejaculation.
Vaginal and anal sex are the most common routes. Oral sex can also transmit chlamydia, though comparing exact risk levels across different types of sex is difficult because most people engage in more than one type. A chlamydia infection in the throat may cause fewer problems than one in the genitals or rectum, but it can still be passed to a partner’s genitals during oral sex.
You don’t need to have had many partners. A single encounter with one infected person is enough. And because the infection so often produces no symptoms, your partner could have been carrying it for weeks or months without knowing. They may have picked it up from a previous relationship and never been tested.
You Didn’t Get It From a Toilet Seat
Chlamydia cannot survive outside the human body for more than a very short time. You cannot catch it from toilet seats, swimming pools, shared towels, hot tubs, or casual contact like hugging or sharing food. The bacteria needs the warm, moist environment of human mucous membranes to survive. If you have chlamydia, sexual contact is how it happened.
Why You Had No Idea
The most common reason people are surprised by a chlamydia diagnosis is that neither they nor their partner ever felt sick. When symptoms do appear, they typically show up one to three weeks after exposure, but many infections never produce noticeable signs at all. In women, symptoms might include unusual vaginal discharge, burning during urination, or bleeding between periods. In men, symptoms can include discharge from the penis, burning with urination, or pain in the testicles.
Because the infection can sit quietly for a long time, it’s often impossible to pinpoint exactly when or from whom you got it. If you’ve had more than one partner in recent months, any of them could have been the source. This is also why the CDC recommends annual screening for all sexually active women under 25 and for older women with new or multiple partners. For men, routine screening is recommended in higher-risk settings or for men who have sex with men.
How Reinfection Happens
One important thing to understand: having chlamydia once does not protect you from getting it again. If you’re treated with antibiotics but your partner isn’t, they will likely pass it right back to you the next time you have sex. This is one of the most common reasons people end up with chlamydia a second time. Both partners need to be treated before resuming sexual contact, or the cycle continues.
Chlamydia is the most frequently reported bacterial infectious disease in the United States, and reinfection is a significant part of that picture. If you’ve been diagnosed, letting your recent partners know so they can get tested and treated isn’t just considerate. It’s the only way to break the chain.
Pregnancy and Childbirth Transmission
Chlamydia can also pass from a mother to her baby during vaginal delivery. In one study, nearly half of infants born vaginally to mothers with active chlamydia infections tested positive for the bacteria. In newborns, chlamydia can cause eye infections (conjunctivitis) and pneumonia. Chlamydia-related pneumonia in infants typically appears one to three months after birth, causing rapid breathing and a distinctive short, choppy cough without fever. The CDC estimates chlamydia causes around 12,000 cases of newborn pneumonia each year in the U.S. This is why prenatal screening is standard.
What This Means Going Forward
Chlamydia is easily curable with a short course of antibiotics, and catching it doesn’t mean anything went dramatically wrong. It means you had unprotected sexual contact with someone who was infected, which is an extremely common scenario given how widespread and silent this infection is. The key steps now are completing your treatment, making sure your partner gets tested and treated, and avoiding sex until both of you have finished your medication.
If you’re under 25 or have new or multiple partners, getting screened for chlamydia once a year (or more often, depending on your situation) catches infections before they cause problems. Left untreated over time, chlamydia can lead to pelvic inflammatory disease in women, which can affect fertility, and can cause painful inflammation in the reproductive tract in men. Routine testing is the simplest way to stay ahead of an infection that rarely announces itself.