Definition of Atypical pneumonia:

Atypical pneumonia refers to pneumonia caused by certain bacteria, including Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae.

This article provides a general overview of atypical pneumonia.

See also:

• Legionella pneumonia (Legionnaire's disease)
• Mycoplasma pneumonia

Causes, incidence, and risk factors:

Atypical pneumonia due to mycoplasma and chlamydophila bacteria usually cause mild forms of pneumonia, unlike other types of the disease that can come on more quickly with more severe early symptoms.

Mycoplasma pneumonia often affects younger people and may be associated with anemia, certain types of rashes, and neurological conditions such as meningitis, myelitis, and encephalitis. For more information on this type of pneumonia, see: Mycoplasma pneumonia

Pneumonia due to chlamydia-related bacteria occurs year round and accounts for 5 - 15% of all pneumonias. It is usually mild with a low death rate.

Atypical pneumonia due to Legionella accounts for 2 - 6% of pneumonias and has a higher death rate. Older adults, smokers, and those with chronic illnesses and weakened immune systems are at higher risk for this type of pneumonia. Breathing in contaminated air (such as that from infected air conditioning systems) has also been linked to pneumonia due to Legionella. For more information on this type of pneumonia, see: Legionnaire's disease