Pneumonia is a respiratory condition in which there is inflammation of the lung.

Community-acquired pneumonia refers to 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

Bronchopneumonia; Community-acquired pneumonia

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:

Pneumonia caused by bacteria tends to be the most serious. 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 impaired (due to AIDS or certain medications that suppress the immune system).
• Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pyogenes, Neisseria meningitidis, Klebsiella pneumoniae, or Haemophilus influenzae are other bacteria that can cause pneumonia.
• Tuberculosis can cause pneumonia in some people, especially those with a weak immune system.

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:

• Cigarette smoking
• Recent viral respiratory infection (common cold, laryngitis, influenza)
• Difficulty swallowing (due to stroke, dementia, Parkinson's disease, or other neurological conditions)
• Chronic lung disease (COPD, bronchiectasis, cystic fibrosis)
• Cerebral palsy
• Other serious illnesses, such as heart disease, liver cirrhosis, or diabetes mellitus
• Living in a nursing facility
• Impaired consciousness (loss of brain function due to dementia, stroke, or other neurologic conditions)
• Recent surgery or trauma
• Immune system problem (See also: Pneumonia in immunocompromised host)

Higgins K, Singer M, Valappil T, Nambiar S, Lin D, Cox E. Overview of recent studies of community-acquired pneumonia. Clin Infect Dis. 2008;47:S150-156.

Centers for Disease Control and Prevention. Recommended Immunization Schedule for Ages 0 - 6 Years. United States, 2009.

Centers for Disease Control and Prevention. Recommended Immunization Schedule for Ages 7 - 18 Years. United States, 2009.

Centers for Disease Control and Prevention. Recommended Immunization Schedule for Adults. United States, 2009.

Li JZ, Winston LG, Moore DH, Bent S. Efficacy of short-course antibiotic regimens for community-acquired pneumonia: a meta-analysis. Am J Med. 2007;120:783-790.

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.