Gastroenterocolitis is a condition characterized by inflammation of the stomach, small intestines, and colon. Gastroenterocolitis is a condition characterized by inflammation of the stomach, small intestines, and colon. The main symptom of gastroenteritis is diarrhea. Other symptoms may include: Because of the symptoms of vomiting and diarrhea, people who have gastroenteritis can become dehydrated quickly. It is very important to watch for signs of dehydration.