Flu, or influenza, is a contagious respiratory disease that infects 10 to 20 percent of U.S. residents. The U.S. Centers for Disease Control and Prevention estimates that an annual average of 114,000 Americans are hospitalized due to flu complications, with 36,000 deaths. The 2003-2004 “flu season” began earlier than expected, with a sudden surge in cases in November 2003; severity was also greater than normal.
