Conditions InDepth: Chlamydia

Chlamydia are bacteria, but they are not capable of surviving on their own. Instead, they can grow only inside other living cells, like viruses. Outside living cells chlamydia are dormant, like spores. In their dormant form, they can travel from one person or animal to another.

There are several different species of chlamydia, and a number of strains within each species that are responsible for a variety of diseases in birds, humans, and other mammals. Their most common appearance is as a sexually transmitted genital infection referred to as chlamydia or nongonococcal urethritis (NGU).

Chlamydia is one of the most common sexually transmitted disease (STD) in the United States, especially among sexually active teens and young adults. Over a million cases were reported to the Centers for Disease Control and Prevention (CDC) in 2006.

This strain also causes Reiter’s syndrome (arthritis, conjunctivitis , and urethritis ) and neonatal infections—pneumonia or conjunctivitis (“pink eye”)—when transferred from an infected mother.

Other types of chlamydia can cause:

  • Another less common STD known as lymphogranuloma venereum (LGV)
  • An eye infection called trachoma or Egyptian ophthalmia that causes millions of cases of blindness in developing nations around the world—This infection is known in developed countries as inclusion conjunctivitis or inclusion blenorrhea
  • Lung, heart, and intestinal infections


Genital chlamydial infections are caused when Chlamydia trachomatis is transmitted during oral, vaginal, or anal sex from an infected partner. Other forms of chlamydia can be transmitted by nonsexual contact, such as flies, dirty hands, or other objects, as well as inhalation and childbirth.

What are the risk factors for chlamydia?
What are the symptoms of chlamydia?
How is chlamydia diagnosed?
What are the treatments for chlamydia?
Are there screening tests for chlamydia?
How can I reduce my risk of chlamydia?
What questions should I ask my doctor?
Where can I get more information about chlamydia?


British Association for Sexual Health and HIV guideline: 2006 UK national guideline for the management of genital tract infection with chlamydia trachomatis. London, England: British Association for Sexual health and HIV(BASHH); 2006

Chlamydia genital infection. EBSCO DynaMed website. Available at: Updated September 2008. Accessed September 18, 2008.

Hollblad-Fadiman K, Goldman SM. American College of Preventive Medicine practice policy statement. Screening for chlamydia trachomatis. Am J Prev Med. 2003;24:287-292

Miller KE. Diagnosis and treatment of chlamydia trachomatis infection. Am Fam Physician. 2006;73:1411-1416.

Sexually transmitted diseases: chlamydia. Centers for Disease Control and Prevention website. Available at: Accessed September 18, 2008.

Last reviewed July 2008 by David L. Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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