Most cases of gastrointestinal flu are actually viral gastroenteritis, because viral infection damages the human gastrointestinal tract, thus showing the corresponding symptoms, which can have systemic symptoms or local symptoms of the gastrointestinal tract, as follows: a. Systemic symptoms include fever, body aches, muscle aches, weakness, and loss of appetite. The symptoms of gastrointestinal tract include nausea, vomiting, abdominal pain and diarrhea. If the amount of vomiting or diarrhea is large enough to cause dehydration, abnormal manifestations related to dehydration may occur, such as dry mouth and thirst, and in severe cases, a drop in blood pressure and even shock.