Influenza is a respiratory disease caused by a virus. The flu is highly contagious and is usually transmitted by coughing and sneezing of an infected person. You can also get the flu by being in contact with an infected person (e.g., shaking hands). Infection is caused 1 to 2 days before symptoms appear and it usually dissipates within 7 days after contamination. This means that the influenza virus can spread before people know they are infected. More than 200,000 people in the United States are hospitalized for flu complications each year and it is estimated that about 36,000 people die from this disease.