Pneumonia is an infection of the alveoli (air sacs) and lower airways in the lungs that causes inflammation and fluid accumulation. There are two main types: community acquired pneumonia (CAP) and nosocomial pneumonia (acquired in the hospital). Many pathogens, including bacteria, fungi, and viruses, can cause pneumonia,[1] but, in some cases, the cause cannot be identified.[2]
What is pneumonia?
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•Last Updated: May 16, 2025
Pneumonia is an infection of the alveoli and lower airways in the lungs that leads to inflammation and fluid accumulation. It can be classified into community-acquired pneumonia and nosocomial pneumonia and is caused by various pathogens, though the cause is sometimes unknown.