Gastroenteritis is an infection in the stomach. Typical symptoms include nausea, vomiting, cramping of the belly (abdominal cramps), diarrhea, fever, and weight loss. Gastroenteritis is usually caused by a viral, bacterial or a parasitic infection, but it is not caused by the influenza virus. It will often go away on its own in 1 to 2 days without needing medical treatment. Make sure you have your child drink fluids to prevent dehydration.