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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

Walking pneumonia; Chlamydophila pneumoniae

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

• Chills
• Confusion (especially with Legionella pneumonia)
• Cough
• Diarrhea (especially with Legionella pneumonia)
• Fever
• General ill feeling
• Headache
• Loss of appetite
• Muscle stiffness and aching
• Rapid breathing
• Rash (especially with Mycoplasma pneumonia)
• Shortness of breath

Persons with suspected pneumonia should have a complete medical evaluation, including a thorough physical exam and a chest x-ray -- especially since the physical exam may not always distinguish pneumonia from acute bronchitis or other respiratory infections.

Depending on the severity of illness, additional studies may be done, include:

• Complete blood count (CBC)
• Blood cultures
• Blood tests for antibodies to specific bacteria
• Bronchoscopy
• Open lung biopsy (only done in very serious illnesses when the diagnosis cannot be made from other sources)
• Sputum culture

Urine tests or a throat swab may be also be done.

Most patients with pneumonia due to mycoplasma or chlamydophila do well with appropriate antibiotic therapy, although there is a small chance that the infection will return if antibiotics are used for less than 2 weeks.

While atypical pneumonias are commonly associated with milder forms of pneumonia, pneumonia due to Legionella, in particular, can be quite severe, especially among the elderly and those with chronic diseases and weakened immune systems. It is associated with a higher death rate.

• Hemolytic anemia (especially with mycoplasma pneumonia)
• Lung failure

Contact your health care provider if you develop a fevers, cough, or shortness of breath. There are numerous causes for these symptoms. The doctor will need to rule out pneumonia.

There is no known prevention for atypical pneumonia. No vaccine is are available at this time for atypical pneumonia.

Limper AH. Overview of Pneumonia. In: Goldman L, Ausiello D. Goldman: Cecil Medicine. Philadelphia, Pa: Saunders; 2007:chap 97.

Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007 Mar 1;44 Suppl 2:S27-72.