Flu (short for influenza) is an acute, contagious respiratory infection. The incubation time following exposure to the flu (via another person) is one to three days, and symptoms come on abruptly with lassitude, malaise, chills, severe pain in the head and back, muscle aches, inflammation of mucous membranes, cough, fever (101° to 103° F) and extreme prostration. Sore throat is a common symptom; less frequently, there are gastrointestinal symptoms including anorexia, nausea and vomiting, but not diarrhea (which indicates a bacterial infection).

Flu is normally a self-limiting disease that lasts from two to seven days. Severe complications of the flu. . . Read More.