Influenza (flu) is a contagious disease caused by influenza viruses that infect the respiratory tract (nose, throat, and lungs). It can cause mild to severe illness, sometimes leading to death. Influenza symptoms often begin suddenly, with fever, headache, tiredness, dry cough, sore throat, nasal congestion and body aches.
Take a look at the ASL (American Sign Language) public service announcement. More information can be found on the Influenza home page.