Add to ORKGInfluenza (the flu) is a contagious respiratory illness caused by influenza viruses. The flu usually comes on suddenly and may cause a cough, fever, chills, sore throat, muscle or body aches, runny or stuffy nose, headaches and fatigue. Some people also have vomiting and diarrhea; however, this is more common in children than adults. The flu is different from a cold or stomach or intestinal disease, which can be caused by many different viruses or bacteria. The flu can cause mild to severe illness and, at times, can lead to death. Most people who get influenza will recover in a few days to less than two weeks. Some people, such as older people, young children and people with certain health conditions, are at high risk for serious flu ...