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Definition

Pneumonia is an infection of the lung, and can be caused by nearly any class of organism known to cause human infections. These include bacteria, viruses, fungi, and parasites. In the United States, pneumonia is the sixth most common disease leading to death. It is also the most common fatal infection acquired by already hospitalized patients. In developing countries, pneumonia ties with diarrhea as the most common cause of death.

Description

Anatomy of the lung

To better understand pneumonia, it is important to understand the basic anatomic features of the respiratory system. The human respiratory system begins at the nose and mouth, where air is breathed in (inspired) and out (expired). The air tube extending from the nose is called the nasopharynx. The...