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Chlamydia trachomatis bacteria

What is chlamydia?

Chlamydia is a common sexually transmitted disease (STD) caused by a bacterium called Chlamydia trachomatis.

Chlamydia infection occurs when Chlamydia trachomatis enters a person's body and multiplies causing tissue damage. Chlamydia infection is a major cause of genital and eye disease.

What causes chlamydia?

Chlamydia is caused by a bacterium, called Chlamydia trachomatis. There are three major human biovars (strains) of this bacteria.

  • One is particularly prevalent in Africa and causes trachoma which is the most common cause of blindness worldwide
  • The second causes lymphogranuloma venereum, which is an STD common among gay men
  • The third biovar is a major cause of pelvic inflammatory disease, ectopic pregnancy, and infertility in women, epididymitis in men, and conjunctivitis and pneumonia in newborns.

Chlamydia is the most frequently reported STD in the United States, with over 2 million new infections occurring every year. This means it is prevalent in the community, particularly among young women.

Chlamydia can be transferred from an infected person to an uninfected person during oral, vaginal, or anal sex. A woman can also pass chlamydia to her baby during childbirth. Reinfection with chlamydia can also occur, even if you have been successfully treated for it if you have unprotected sex with someone who has it.

What are the symptoms of chlamydia infection?

Chlamydia can infect the cervix, rectum, or throat in women; and the urethra (inside the penis), rectum, or throat in men. Most women with chlamydia have no symptoms and do not realize they have it. Men usually don’t have any long-term health problems from chlamydia, although rarely it may cause infertility.

In people who do develop symptoms, symptoms may not appear until weeks after sex with an infected partner.

Symptoms in women may include:

  • An abnormal vaginal discharge which may smell strongly
  • A burning sensation when passing urine
  • Pain during intercourse
  • Lower abdominal pain and nausea if the infection has spread

Symptoms in men may include:

  • A discharge from the penis
  • A burning sensation when passing urine
  • Burning or itching around the opening of the penis
  • Uncommonly, pain and swelling in one or both testicles

A chlamydia infection of the rectum can cause rectal pain, discharge, or bleeding.

Both men and women can develop reactive arthritis after chlamydia infection, and it may also increase the risk of premature labor in pregnant women.

How is chlamydia diagnosed?

Because the bacteria are so prevalent in the community, and most women are asymptomatic, the CDC recommends annual chlamydia screening for all sexually active women younger than 25 years or women aged 25 years or older with new or multiple sex partners. Chlamydia may be screened for by using a urine test or a vaginal swab.

Women with symptoms of chlamydia and all pregnant women at their first prenatal visit should be tested for chlamydia.

A urine test is also used to test for chlamydia in men with symptoms, and a urethral swab may also be taken to rule out gonorrhea.

How is chlamydia infection treated?

Treatment of chlamydia is usually with antibiotics given either as a one day or 7-day course.

Sex should be avoided until completion of the 7-day antibiotic course or for at least 7 days after a single dose of antibiotics. Chlamydia should be retested for three months after treatment.

Untreated chlamydia infection:

  • Can be passed onto others
  • Is a major cause of pelvic inflammatory disease (PID), which is a major cause of infertility, ectopic pregnancy, and chronic pelvic pain
  • Can facilitate the transmission of HIV infection
  • Can be passed from a pregnant woman to her infant during delivery, potentially resulting in pneumonia and ophthalmia neonatorum, which can lead to blindness

How is chlamydia infection prevented?

Using condoms, avoiding oral or anal sex, and having only one sexual partner may reduce the incidence of Chlamydia.

All sexually active women younger than 25 years, women aged 25 years or older with new or multiple sex partners, or men who have sex with men should be screened annually for chlamydia.