Pneumonia


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Definition

Pneumonia is a breathing (respiratory) condition in which there is an infection of the lung.

Community-acquired pneumonia is pneumonia in people who have not recently been in the hospital or another health care facility (nursing home, rehabilitation facility).

See also: Hospital-acquired pneumonia


Alternative Names

Bronchopneumonia; Community-acquired pneumonia


Causes, incidence, and risk factors

Pneumonia is a common illness that affects millions of people each year in the United States. Germs called bacteria, viruses, and fungi may cause pneumonia.

Ways you can get pneumonia include:

  • Bacteria and viruses living in your nose, sinuses, or mouth may spread to your lungs.
  • You may breathe some of these germs directly into your lungs.
  • You breathe in (inhale) food, liquids, vomit, or fluids from the mouth into your lungs (aspiration pneumonia)

Pneumonia caused by bacteria tends to be the most serious kind. In adults, bacteria are the most common cause of pneumonia.

  • The most common pneumonia-causing germ in adults is Streptococcus pneumoniae (pneumococcus).
  • Atypical pneumonia, often called walking pneumonia, is caused by bacteria such as Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae.
  • Pneumocystis jiroveci pneumonia is sometimes seen in people whose immune system is not working well.

Many other bacteria can also cause pneumonia.

Viruses are also a common cause of pneumonia, especially in infants and young children.

See also: Respiratory syncytial virus

Risk factors (conditions that increase your chances of getting pneumonia) include:


References

Van der Poll T, Opal SM. Pathogenesis, treatment, and prevention of pneumococcal pneumonia. Lancet. 2009;374:1543-1556.

Niederman M. In the clinic. Community-acquired pneumonia. Ann Intern Med. 2009;151(7).

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.

Torres A, Menéndez R, Wunderink R. Pyogenic bacterial pneumonia and lung abscess. In: Mason RJ, Broaddus VC, Martin TR, et al. Murray & Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 32.


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Review Date: 5/1/2011
Reviewed By: Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care. University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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Last Updated 7/5/2011
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