A highly contagious infection, the flu (influenza) is spread easily from person to person. It often causes symptoms like chills, fever, and a cough. Like the common cold, it is caused by a virus; however, there are a few differences between the flu and a cold. For example, the flu virus often causes symptoms that are not seen with a cold, such as extreme exhaustion and headaches.
The flu is usually a mild disease in healthy children, young adults, and middle-aged people. However, in older adults and people with certain chronic illnesses, it can be life-threatening.
(For more information on this topic, click Flu. This full-length eMedTV article talks about when outbreaks are most likely to occur, who is most at risk, and more.)