Chlamydial pneumonia is a lower respiratory tract infection caused by C. pneumoniae, a bacterial pathogen that can also produce upper respiratory tract involvement, bronchitis, or pneumonia through damage to the respiratory lining [1]. The organism was formerly termed Chlamydophila pneumoniae [1].
Disease overview
Bacterial Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026
Chlamydial pneumonia is a respiratory illness caused by the bacterium Chlamydia pneumoniae, which can affect the upper or lower respiratory tract [1]. Initial infection typically occurs in school-aged children or young adults, with reinfection more common among older adults [1]. No vaccine is currently available for prevention [1].
Read the full clinical and epidemiological profile 6
Affected individuals commonly experience fatigue, headache, hoarseness, low-grade fever, runny nose, sore throat, and a gradually worsening cough [1]. Laryngitis is relatively frequent compared with other bacterial pneumonias, and symptoms may persist for several weeks; serious complications are uncommon [1]. Some infected persons remain asymptomatic, with an incubation period of approximately three to four weeks [1].
First infections most often appear in school-aged children or young adults, whereas older adults bear a higher burden of reinfection and severe disease [1]. Outbreaks can arise in crowded environments where respiratory droplet exposure is concentrated [1].
The bacteria are passed between people through cough- or sneeze-generated respiratory droplets that reach another person's mouth or nose, with contaminated hands or surfaces also capable of spreading the organism [1].
Covering coughs and sneezes together with regular hand hygiene reduces opportunities for transmission [1]. No vaccine exists against C. pneumoniae, and antibiotic prophylaxis after exposure is not routinely recommended [1]. Repeated infection is possible, so general hygienic measures remain the main preventive approach [1].
- 1 US Centers for Disease Control and Prevention. About Chlamydia pneumoniae Infection | C. pneumoniae | CDC [Internet]. cited 23 Oct 2026. Available from: https://www.cdc.gov/cpneumoniae/about/index.html
- 2 Yang K et al. Case series and literature review of chlamydial ophthalmia neonatorum in Botswana. Int J STD AIDS. 2023 Oct. PMID: 37338101. doi: 10.1177/09564624231173028. PubMed: https://pubmed.ncbi.nlm.nih.gov/37338101/
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