Pneumonia is a serious infection and/or inflammation of the lungs. The air sacs in the lungs fill with pus and other liquid, and oxygen has trouble reaching the blood. When oxygen is limited in the bloodstream, body cells cannot work properly. When this process occurs, in conjunction with the spread of infection in the body; pneumonia can cause death. 

Pneumonia can be caused by over 30 different reasons. However, there are five main causes of pneumonia:

• Bacteria

• Viruses

• Mycoplasmas (mycoplasmas are the smallest free-living agents of disease in humankind, not classified as bacteria or viruses, but having characteristics of both)

• Other infectious agents, such as fungi

• Exposure to various chemicals

Pneumonia hospital admissions are fairly common, however appropriate treatment is important as pneumonia is a leading cause of death in the United States. Better processes of care in hospitals may reduce the risk of death (mortality) from pneumonia.