Pneumonia is caused by a variety of agents such as bacteria, viruses, and mycoplasmas, among others.
In 1996, pneumonia resulted in 54.6 million restricted-activity days and 31.5 million bed days. There were 90,147 pneumonia deaths recorded in the United States in 1998. Pneumonia affects the lungs in two ways. Lobar pneumonia affects a lobe of the lungs, and bronchial pneumonia can affect patches throughout both lungs. The major types of pneumonia are bacterial pneumonia, viral pneumonia, and mycoplasma pneumonia.