Is it a Cold? Or is it the Flu?

What is the flu? The flu is a contagious infection of the nose, throat, and lungs caused by the influenza virus. Sometimes people confuse cold and flu, which share some of the same symptoms and occur at the same time of the year (cold and flu season). However, the two diseases are very different. Most people get a cold several times each year, and the flu only once every several years.