Disease Specifics

Chlamydia pneumoniae infection has a wide spectrum of clinical symptoms and a long incubation period of 3 to 4 weeks. The varied clinical presentation and lack of standardized diagnostic methods make identifying and appropriately treating patients challenging.

Since C. pneumoniae infection is likely underdiagnosed, the actual number of cases each year is unknown. Primary infection occurs mainly in school-aged children or young adults, while reinfection is most common in older adults.

photo of developmental cycle, Reprinted by permission from Macmillan Publishers Ltd

Reprinted by permission from Macmillan Publishers Ltd: Bryne GI, Ojcius DM. Chlamydia and apoptosis: life and death decisions of an intracellular pathogen.external icon Nature Rev. Microbiol. 2004. 2(10):802-8.

Chlamydia pneumoniae

C. pneumoniae (formerly called Chalmydophila pneumoniae), along with Chlamydia psittaci and Chlamydia trachomatis, are members of the bacterial family Chlamydiaceae. The Chlamydiaceae family shares a unique developmental cycle that is different from all other bacteria.

C. pneumoniae growth consists of two alternating forms: elementary and reticulate bodies. Elementary bodies are metabolically inactive. They infect the host when cells ingest the elementary bodies through the process of receptor-mediated endocytosis. Once inside the cell, the elementary bodies differentiate into reticulate bodies, which are metabolically active but noninfectious. The reticulate bodies rely on the host cell for adenosine triphosphate (ATP) synthesis. The reticulate bodies divide by binary fission and induce a host immune response. After 48 to 72 hours, the reticulate bodies reorganize themselves and condense to form new elementary bodies. The elementary bodies then leave the host cell and start a new infectious cycle. Since C. pneumoniae growth takes place within host cells, culture requires growth within eukaryotic cells rather than on cell-free culture media.


C. pneumoniae cannot survive outside the host for very long. For this reason, the bacteria are usually transmitted from close person-to-person contact by respiratory droplets. C. pneumoniae can also infect people who touch surfaces contaminated with these droplets and then touch their nose or mouth.

In the past 20 years, researchers have linked a wide variety of diseases to C. pneumoniae infection including:

  • Atherosclerotic cardiovascular disease
  • Multiple sclerosis
  • Asthma
  • Age-related macular degeneration
  • Alzheimer’s disease
  • Chronic fatigue syndrome
  • Chronic skin wounds

However, researchers have not been able to confirm a causal relationship between these diseases and C. pneumoniae infection.


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  • Burillo A, Bouza E. Chlamydophila pneumoniaeInfect Dis Clin N Am. 2010;24:61–71.
  • Cunha BA. The atypical pneumonias: Clinical diagnosis and importance. Clin Microbio Infect. 2006;12:12–24.
  • Kuo CC, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clin Microbiol Reviews. 1995;8(4):451–61.
Page last reviewed: November 15, 2021