Yes, chlamydia is a bacterial infection. It’s caused by the bacterium Chlamydia trachomatis, and it’s one of the most commonly reported bacterial infections in the United States, contributing to over 2.2 million combined cases of chlamydia, gonorrhea, and syphilis reported in 2024. Because it’s bacterial, chlamydia is curable with antibiotics, which sets it apart from viral sexually transmitted infections like herpes or HIV.
What Kind of Bacterium Causes It
Chlamydia trachomatis is an unusual bacterium. Unlike most bacteria, which can survive on surfaces or in bodily fluids on their own, C. trachomatis is an obligate intracellular parasite. That means it can only survive and reproduce inside your cells. This is part of why chlamydia behaves differently from other bacterial infections and why it can be so sneaky.
The bacterium has a two-stage life cycle. The first form, called an elementary body, is tiny (about 0.3 micrometers) and essentially dormant, almost spore-like. This is the form that spreads between people. It attaches to a cell, gets inside, and then transforms into a larger, active form called a reticulate body. This active form divides repeatedly inside the cell, eventually producing new dormant particles that burst out and infect neighboring cells. This cycle of hiding inside cells is one reason the immune system often fails to clear the infection on its own and why symptoms can be absent for weeks or months.
Why Most People Don’t Notice Symptoms
Chlamydia often produces no symptoms at all. Many people carry the infection without knowing it, which is a major reason it spreads so easily and why routine screening matters.
When symptoms do show up, they tend to be mild and easy to dismiss. In women, the most common signs are unusual vaginal discharge and a burning feeling when urinating. In men, symptoms typically include discharge from the penis, burning during urination, and occasionally pain or swelling in one or both testicles. Rectal infections, which can occur through anal sex, may cause rectal pain, discharge, or bleeding.
Because symptoms are absent or subtle in many cases, the CDC recommends annual chlamydia screening for sexually active women under 25, as well as for older women with new or multiple partners.
How Chlamydia Is Diagnosed
Testing for chlamydia is straightforward. The standard method uses a nucleic acid amplification test, which detects genetic material from the bacterium. These tests are highly accurate, with sensitivity usually well above 90% and specificity at 99% or higher. They pick up 20% to 50% more infections than older testing methods like culture.
You can be tested using a urine sample or a swab (vaginal, cervical, urethral, or rectal, depending on the site of potential exposure). One thing to know: if you’ve recently been treated for chlamydia, residual bacterial DNA can trigger a positive result for up to three weeks after finishing antibiotics, even though the infection is gone. For that reason, a follow-up test right after treatment isn’t always useful.
Treatment Is Simple and Effective
Because chlamydia is bacterial, antibiotics cure it. The current first-line treatment is a seven-day course of doxycycline, taken twice daily. A single-dose alternative exists for situations where a week-long course isn’t practical. Both options are highly effective.
One of the reassuring things about chlamydia, compared to infections like gonorrhea, is that antibiotic resistance remains extremely rare. National surveillance studies across multiple countries have consistently found that C. trachomatis is still highly susceptible to standard treatments. Isolated cases of resistance have been documented in lab settings, but they haven’t become a meaningful clinical problem.
After treatment, the CDC recommends retesting three months later. This isn’t because the antibiotics failed. It’s to catch reinfection, which is common when sexual partners haven’t been treated at the same time. You should avoid sex for seven days after completing treatment (or until a single-dose treatment has had time to work) to prevent passing the infection back and forth.
What Happens If It Goes Untreated
Left alone, chlamydia can cause serious damage, particularly in women. About 10% to 15% of women with untreated chlamydia develop pelvic inflammatory disease, an infection of the uterus, fallopian tubes, and surrounding tissues. PID can cause chronic pelvic pain and scarring that leads to infertility or ectopic pregnancy, where a fertilized egg implants outside the uterus.
What makes this especially concerning is that fallopian tube damage can happen without any noticeable symptoms. A woman may never know she had chlamydia until she has difficulty getting pregnant years later. This “silent” infection in the upper reproductive tract is one of the leading preventable causes of infertility.
In men, untreated chlamydia can spread to the tube that carries sperm from the testicle, causing pain and swelling. While fertility complications in men are less common than in women, they do occur. Rectal infections left untreated can also lead to ongoing discomfort and inflammation.
How It Spreads and How to Reduce Risk
Chlamydia spreads through vaginal, anal, or oral sex with someone who has the infection. It can also be passed from mother to baby during childbirth, potentially causing eye infections or pneumonia in the newborn. It does not spread through casual contact like hugging, sharing food, or using the same toilet.
Condoms significantly reduce the risk of transmission when used consistently. Because chlamydia is so often asymptomatic, regular screening is the most practical way to catch and treat infections before they cause harm or spread to partners. If you test positive, notifying recent sexual partners so they can also get tested and treated is one of the most effective ways to break the cycle of reinfection.