We've all had it.  It's the flu we catch from our family, friends and co-workers, usually during the fall.  It is a respiratory infection caused by influenza viruses, spread when infected people sneeze or cough. Usually people get sick one to three days after they have been exposed.  About 36,000 Americans die every year from the flu.  Most people can prevent or reduce flu symptoms by getting an annual flu shot, washing their hands before eating or drinking, and staying away from others who are sick.