Pneumonia is a respiratory condition in which there is infection 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).
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 secretions from the mouth into your lungs (
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.
Risk factors (conditions that increase your chances of getting pneumonia) include:
- Chronic lung disease (
COPD, bronchiectasis, cystic fibrosis)
- Cigarette smoking
- Difficulty swallowing (due to
stroke, dementia, Parkinson's disease, or other neurological conditions)
- Immune system problem (See also:
Pneumonia in immunocompromised host)
- Impaired consciousness (loss of brain function due to dementia, stroke, or other neurologic conditions)
- Living in a nursing facility
- Other serious illnesses, such as
heart disease, liver cirrhosis, or diabetes mellitus
- Recent surgery or trauma
- Recent viral respiratory infection (common cold,