Influenza is a potentially life-threatening, contagious disease that is caused by a virus.
When influenza attacks the lungs, the lining of the respiratory tract is damaged. The tissues temporarily become swollen and inflamed but usually heal within two or more weeks. Influenza and pneumonia combined are the sixth leading cause of death among all Americans and the fifth leading cause of death among all Americans over the age of 65. Influenza and pneumonia together resulted in 91,871 deaths in 1998. Influenza caused 1,724 deaths alone.