Influenza is a highly contagious disease of the respiratory tract.
It is caused by a virus. The disease comes on suddenly, with fever, chills, cough, general aches and pains, and a feeling of tiredness and weakness. Influenza symptoms usually last for a few days to a week and go away without treatment. However, in some people influenza can cause severe illness or death. It is estimated that more than 10,000 Americans die of influenza each year.