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Atypical pneumonia

Definition:
Atypical pneumonia refers to pneumonia caused by certain bacteria -- namely, Legionella pneumophila, Mycoplasma pneumoniae and Chlamydia pneumoniae. While atypical pneumonias have been commonly associated as a whole with milder forms of pneumonia, pneumonia due to Legionella, in particular, can be quite severe and lead to high mortality rates.

Alternative Names:
Walking pneumonia

Causes, incidence, and risk factors:

Atypical pneumonia due to Mycoplasma and Chlamydia usually cause milder forms of pneumonia and are characterized by a more protracted course of symptoms unlike other forms of pneumonia which can come on more quickly with more severe early symptoms.

Mycoplasma pneumonia often affects younger people and may be associated with manifestations outside of the lungs (such as anemia and rashes), and neurological syndromes (such as meningitis, myelitis, and encephalitis). Severe forms of Mycoplasma pneumonia have been described in all age groups.

Chlamydia pneumonia occurs year round and accounts for 5-15% of all pneumonias. It is usually mild with a low mortality rate. In contrast, atypical pneumonia due to Legionella accounts for 2-6% of pneumonias and has a higher mortality rate.

Elderly individuals, smokers, and people with chronic illnesses and weakened immune systems are at higher risk for this type of pneumonia. Contact with contaminated aerosol systems (like infected air conditioning systems) has also been associated with pneumonia due to Legionella.



Review Date: 3/14/2002
Reviewed By: Rocio Hurtado, M.D., Infectious Diseases Division, Massachusetts General Hospital and Brigham and Women's Hospital, Boston, MA. Review provided by VeriMed Healthcare Network.

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