Definition of Pneumonia:

Pneumonia is an infection of the lungs. Many different organisms can cause it, including bacteria, viruses, and fungi.

Causes, incidence, and risk factors:

Pneumonia is a common illness that affects millions of people each year in the United States.

Bacterial pneumonias tend to be the most serious and, in adults, the most common cause of pneumonia. The most common pneumonia-causing bacterium in adults is Streptococcus pneumoniae (pneumococcus).

Respiratory viruses are the most common causes of pneumonia in young children, peaking between the ages of 2 and 3. By school age, the bacterium Mycoplasma pneumoniae becomes more common.

In some people, particularly the elderly and those who are debilitated, bacterial pneumonia may follow influenza or even a common cold.

People who have trouble swallowing are at risk of aspiration pneumonia. In this condition, food, liquid, or saliva accidentally goes into the airways. It is more common in people who have had a stroke, Parkinson's disease, or previous throat surgery.

It is often harder to treat pneumonia in people who are in a hospital, or a nursing facility.

See also:

• Aspiration pneumonia
• Atypical pneumonia
• CMV pneumonia
• Hospital-acquired pneumonia
• Legionella pneumonia
• Pneumocystis carinii pneumonia
• Pneumonia in immunocompromised host
• Viral pneumonia
• Walking pneumonia