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Epidemiology of Chlamydia trachomatis infections

Jeanne Marrazzo, MD, MPH, FACP, FIDSA
Section Editor
Noreen A Hynes, MD, MPH, DTM&H
Deputy Editor
Allyson Bloom, MD


Chlamydia trachomatis is a sexually transmitted gram-negative bacterium that causes infection worldwide. In the US, it is the most commonly reported bacterial infection and a common cause of urethritis in men and cervicitis in women [1]. The largely asymptomatic reservoir of infections provides an ongoing source for efficient disease transmission and also allows for silent disease. C. trachomatis infection can result in scarring of the Fallopian tubes, ovaries, endometrial lining, and occasionally, the adjacent perineum, which increases the risk of future ectopic pregnancy and tubal infertility [2]. These consequences are the main reason that C. trachomatis is estimated to be the most costly nonviral sexually transmitted infection [3]. With this in mind, screening programs aimed at preventing pelvic inflammatory disease (PID) in women began in the late 1980s in the US, and were formally endorsed by the US Preventive Screening Task Force (USPSTF) and other major organization in the mid-1990s [4]. Other countries also have national chlamydia screening programs [5].

The epidemiology of C. trachomatis infection in adolescents and adults is discussed in this topic. The screening, clinical manifestations, diagnosis, and treatment of chlamydial infections in adolescents and adults are discussed in detail elsewhere. (See "Screening for sexually transmitted infections", section on 'Chlamydia and gonorrhea' and "Clinical manifestations and diagnosis of Chlamydia trachomatis infections" and "Treatment of Chlamydia trachomatis infection".)

Lymphogranuloma venereum, endemic trachoma, and chlamydia infections in the newborn are discussed in detail elsewhere. (See "Lymphogranuloma venereum" and "Trachoma" and "Chlamydia trachomatis infections in the newborn".)


C. trachomatis is a small gram-negative bacterium that is an obligate intracellular parasite. It has a distinct life-cycle consisting of two major phases:

The small elementary bodies attach and penetrate into cells, changing into the metabolically active form, called the reticulate body, within six to eight hours. These forms create large inclusions within cells.

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Literature review current through: Nov 2017. | This topic last updated: Oct 25, 2017.
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