Chlamydia is a sexually transmitted infection (STI) that can result in many types of infections in both women and men. It is the most commonly reported infectious disease in the US, even though many cases go unreported because people do not know they have it. Chlamydia can cause serious reproductive complications if left untreated. The good news is that chlamydia is detectable, curable, and easy to treat.
Chlamydia is caused by a specific bacterium called Chlamydia trachomatis. It is transmitted via body fluids through oral, vaginal, or anal sex with an infected partner. The bacterium infects the cervix (entrance to the uterus), urethra (the tube that carries urine from the body), rectum, or throat depending on the route of transmission. You can transmit and acquire chlamydia without ejaculation.
Transmission can also occur from an infected mother to a newborn during childbirth. The baby is exposed to the bacteria in the birth canal, which may cause conjunctivitis (an eye infection) or pneumonia (a lung infection).
2015 Sexually transmitted diseases treatment guidelines. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/std/tg2015/default.htm. Updated January 25, 2017. Accessed February 16, 2018.
Chlamydia. Merck Manual Professional Version website. Available at:
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Updated April 2016. Accessed February 16, 2018.
Chlamydia—CDC fact sheet (detailed). Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/std/chlamydia/STDFact-chlamydia-detailed.htm. Updated September 26, 2017. Accessed February 16, 2018.
Chlamydia genital infection. EBSCO DynaMed Plus website. Available at: https://www.dynamed.com/topics/dmp~AN~T114223/Chlamydia-genital-infection . Updated August 23, 2017. Accessed February 16, 2018.
de Vrieze NH, de Vries HJ. Lymphogranuloma venereum among men who have sex with men. An epidemiological and clinical review. Expert Rev Anti Infect Ther. 2014;12(6):697-704.
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Last reviewed March 2018 by
EBSCO Medical Review Board
David L. Horn, MD, FACP
Last Updated: 3/15/2015