Infections are caused by the bacterium Chlamydia trachomatis, the most commonly reported sexually transmitted infection in the US.[4] It is almost always transmitted by sexual contact. The bacterium may cause symptoms, but in most people the infection is asymptomatic.[1]


Chlamydia trachomatis is a small gram-negative bacterium that lives as an obligate intracellular parasite.[5] It has two life-cycle phases. During the first phase, the organism enters the cell and forms large inclusion bodies called elementary bodies. The elementary bodies reorganize into smaller, reticulate bodies. The reticulate bodies replicate and mature back into elementary bodies. Once the maturation is complete, the cell ruptures within 2 to 3 days. The freed bacteria then penetrate other cells to continue the replication process.[6] Due to this unique life cycle, the organism cannot be cultured on artificial media.[7]

After exposure to C trachomatis, the incubation period is usually 7 to 21 days. Infection in the urogenital tract leads to urethral inflammation in men or cervical inflammation in women. In some cases, the infection can migrate up into the reproductive tract in women and cause an infection in the pelvis, pelvic inflammatory disease (PID), or perihepatitis (Fitzhugh-Curtis syndrome). In men, ascension of the infection can lead to epididymitis or prostatitis.[2]


Serotypes L1, L2, L3

Lymphogranuloma venerum (LGV): more invasive serotype causing genital ulcer and/or inguinal lymphadenopathy, or proctitis with rectal infection.

Serotypes A, B, Ba, C

Ocular trachoma.

Serotypes B, Ba, D through K

Oculogenital disease in adults and children, infant pneumonia.

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