Chlamydia

Chlamydia is a common term for infection with any bacterium belonging to the phylum Chlamydiae. This term derives from the name of the bacterial genus Chlamydia in the family Chlamydiaceae, order Chlamydiales, class and phylum Chlamydiae, ultimately from Greek χλαμύδος "cloak". There are two genera in Chlamydiaceae: Chlamydia and Chlamydophila. The genus Chlamydia includes three species: C. trachomatis, C. muridarum, and C. suis. C. trachomatis infection is described below.

Chlamydia trachomatis is a major infectious cause of human eye and genital disease. C. trachomatis is naturally found living only inside human cells and is one of the most common sexually transmitted infections in people worldwide — about four million cases of chlamydia infection occur in the United States each year. Not all infected people exhibit symptoms of infection. About half of all men and three-quarters of all women who have chlamydia have no symptoms and do not know that they are infected. It can be serious but is easily cured with antibiotics if detected in time. Equally important, chlamydia infection of the eye is the most common cause of preventable blindness in the world. Blindness occurs as a complication of trachoma (chlamydia conjunctivitis).

There are many other species of Chlamydiae that live in the cells of animals (including humans), insects, or protozoa. Two of these species cause lung infection in humans: Chlamydophila pneumoniae and Chlamydophila psittaci. Both of these species previously belonged to the genus Chlamydia.