An acute respiratory viral infection characterized by fever, chills, sore throat, headache, body aches, and severe cough; it is commonly known as the flu. While many viruses can cause respiratory infections such as the common cold, influenza viruses are more likely to cause severe illness and to result in serious medical complications. Although gastrointestinal symptoms may sometimes accompany influenza infection, especially in children, the term “stomach flu” is a misnomer for gastrointestinal illnesses caused by a variety of other viruses, bacteria, or other agents.