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Pneumonia caused by Chlamydia species in children

Dori F Zaleznik, MD
Jesus G Vallejo, MD
Section Editors
Morven S Edwards, MD
Robert A Wood, MD
Deputy Editor
Mary M Torchia, MD


The Chlamydia species are obligate, intracellular bacteria. Chlamydia trachomatis is a major cause of genital tract and ocular infections worldwide. (See "Chlamydia trachomatis infections in the newborn" and "Clinical manifestations and diagnosis of Chlamydia trachomatis infections" and "Treatment of Chlamydia trachomatis infection".)

Chlamydia pneumoniae and less often Chlamydia psittaci cause atypical pneumonia. C. trachomatis typically causes conjunctivitis and/or pneumonia in neonates but also may affect young infants [1]. (See "Pneumonia in children: Epidemiology, pathogenesis, and etiology" and "Psittacosis" and "Chlamydia trachomatis infections in the newborn".)


Chlamydia species are unusual bacteria in several ways. The genome of the organisms is only 660 million daltons, smaller than any other prokaryote except mycoplasma. They do not contain a peptidoglycan in the cell wall. The growth cycle of the organism is complex and biphasic, consisting of two distinct entities: elementary (EB) and reticulate bodies (RB) [2].

The form in which the bacterium multiplies is the RB, which is intracellular. Replication occurs within a membrane-bound inclusion. RB are unstable and revert to EB within the inclusion, which then ruptures, causing release of EB, which are the form that survives in the extracellular environment; EB are the infectious particles.

The signal that triggers RB to EB reversion is not known. EB attach to epithelial cells and enter cells via a phagosome. Once inside, EB reorganize to RB, which then replicate. Polymorphic membrane proteins are found on the surface of EBs of multiple Chlamydia species including C. psittaci and may induce antibody production [3].

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Literature review current through: Nov 2017. | This topic last updated: Apr 12, 2017.
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