Understanding Chlamydia — the Basics

What Is Chlamydia?

Chlamydia is the most common bacterial sexually transmitted disease (STD) in the U.S. One in four Americans have it. Scientists believe it’s twice as common as gonorrhea and 30 times as common as syphilis. You can contract it more than once.

The good news is that chlamydia is easily cured by antibiotics. The bad news is that most people who get chlamydia don’t have symptoms or know that they have it. Only 10% of men and 5%-30% of women who have a lab test that confirms the disease even develop symptoms. About 30% of these women develop serious complications such as damage to the fallopian tubes (the tubes that connect the ovaries to the uterus). This damage is caused by pelvic inflammatory disease and may result in infertility. Damage to the fallopian tubes can also increase the risk of ectopic pregnancy (when the fertilized egg implants outside of the uterus). Untreated chlamydia in pregnancy may result in premature birth.

The infection can be passed on to an unborn child and cause serious complications. Babies born to infected mothers may suffer from pneumonia or conjunctivitis, an inflammation of membranes in the eye that may lead to blindness. Pregnant women are screened because it is so common to be without symptoms, and the consequences for the fetus/infant can be serious.

Men with chlamydia are less likely to have symptoms. If they do, their most common symptoms are pain with urination and a mucousy or watery discharge. Men can develop a chlamydia urethritis (and infection of the tube that drains urine from the bladder) and symptoms of discharge from their penis or burning when urinating. They may develop epididymitis or orchitis, an inflammation of the testicles that can cause infertility.

What Causes Chlamydia?

Chlamydia is caused by the bacterium Chlamydia trachomatis. The disease is spread by oral, vaginal, or anal sex.


  1. https://www.webmd.com/sexual-conditions/understanding-chlamydia-basics
  2. Mayo Clinic: “Chlamydia."
  3. AMA: “Chlamydia Screening: A Routine Test."
  4. CDC: “Chlamydia — CDC Fact Sheet."
  5. National Institutes of Allergy and Infectious Diseases: “Chlamydia."
  6. Johns Hopkins Medicine. 
  7. UpToDate.com.

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