What is chlamydia?

Chlamydia infection is a sexually transmitted infection (STI) caused by the bacteria Chlamydia trachomatis.

How common is chlamydia?

Chlamydia is the most common notifiable STD in the U.S. There were 1.5 million new cases reported in 2016.1 Chlamydia occurs in both men and women, but is most often seen in young women under the age of 25, with young minority women being the hardest hit.2 About twice as many cases reported in females than in males.1

How is chlamydia spread?

Chlamydia infection can be spread through vaginal, anal, or oral sex. It is more easily transmitted from male to female. Mothers of newborn infants can transmit the infection during childbirth.

Does chlamydia cause symptoms?

Most of the time, a chlamydia infection does not cause symptoms. ¾ females and ½ of males have no symptoms.2 Chlamydia is known as a “silent disease” because most people who are infected do not have symptoms. Without symptoms, infected people can spread the chlamydia infection to their sexual partners without knowing it. Yearly screening tests are recommended for people at high risk for chlamydia, even when they do not have symptoms: (1) sexually active females under 25 years of age; (2) females over 25 years whose sexual practices put them at risk for infection; and (3) all pregnant females and (4) men who have sex with men.3

What are the symptoms of chlamydia?

Some people do get symptoms when they have a chlamydia infection. Symptoms of chlamydia in women can include inflammation of the cervix, abdominal pain, abnormal vaginal discharge and painful urination. Urethral infections in males may cause discharge from the penis and painful urination. If the chlamydia infection involves the anus and rectum, pain, discharge, and bleeding in both males and females can occur.2

Are there any treatments available for chlamydia?

Chlamydia infection can be treated with antibiotics regardless of the site of infection. Sex partners should also be treated and sexual activity should stop during the treatment. Not receiving treatment and treatment delay can lead to serious health problem. Treatment does not reverse existing complications.4

What complications can result from chlamydia?

One potential complication of chlamydia infection in a female is pelvic inflammatory disease (PID). PID occurs when vaginal or cervical infections travel to the upper genital tract and infect the lining of the uterus and the fallopian tubes. Sometimes the infection causes abscesses in the tubes and ovaries and the infection spreads into the pelvic cavity. PID is associated with long-term problems including chronic pelvic pain, ectopic pregnancy, and infertility.5

Another possible complication of chlamydia infection is the spread of the infection from a mother to her baby. If the mother is infected, newborn infants may acquire diseases like conjunctivitis and pneumonia at the time of childbirth.

Does chlamydia affect the spread of HIV?

Chlamydia infection increases the chance of getting HIV if exposed. HIV targets CD4 cells that are produced by the body to fight off chlamydia and causes HIV to spread throughout the body.

Can chlamydia be prevented?

Yes; chlamydia can be prevented by refraining from sexual activity until a person is in a lifelong, mutually monogamous relationship with an uninfected partner. Mothers should be screened for chlamydia infection during pregnancy to prevent the spread of chlamydia infection to their babies.


This is a healthy appearing cervix. Many females infected with chlamydia have cervixes that appear normal. This picture was kindly provided by W. David Hager, MD, FACOG, of the Women’s Care Center in Lexington, KY.


This is an image of a cervix affected by chlamydia. Pus and inflammation are present. This picture was kindly provided by W. David Hager, MD, FACOG, of the Women’s Care Center in Lexington, KY.


  1. Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance, 2016. Atlanta: U.S. Department of Health and Human Services; 2017. Available at: Accessed October 2017
  2. Grimes, Jill (editor), Sexually Transmitted Disease: An Encyclopedia of Diseases, Prevention, Treatment, and Issues, 2014 Greenwood Publishers, Santa Barbara, Ca.
  3. Centers for Disease Control and Prevention, “Sexually Transmitted Diseases Treatment Guidelines, 2015,” MMWR June 5, 2015, Vol. 63/No 3
  4. Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines 2015. MMWR 2015 Vol. 64/No. 3 Available at:   Accessed December 2015.
  5. Sweet,RL, “Treatment of Acute Pelvic Inflammatory Disease,” Infect Dis Obstet Gynecol. 2011; 2011:561909 accessed Dec 2015
  6. Sowadsly, Rick, “The HIV-STD Connection”, The Body: The Complete HIV/AIDS Resource, March 2009


Updated: November 2017