influenza

influenza An illness caused by viruses that infect the respiratory tract. These viruses are divided into three types, designated A, B, and C. Symptoms of influenza include fever, appetite loss, an achy feeling throughout the body, and weakness. Most people who get influenza recover completely in 1 to 2 weeks, but some people develop serious and potentially lifethreatening medical complications, such as pneumonia. Much of the illness and death caused by influenza can be prevented by annual influenza vaccinations. Commonly known as flu. See also influenza vaccine.