Symptoms of Gastroenteritis Gastroenteritis is an acute illness that usually lasts between 1-2 days. However, symptoms may take 1-3 days to develop depending upon the causative agent and may range from slight discomfort to severe dehydration which can be fatal especially in children. Gastroenteritis - Learn about the causes, symptoms, diagnosis & treatment from the Merck Manuals - Medical Consumer Version. Learn about gastroenteritis (stomach flu), its symptoms, causes, and types. Discover effective treatment options to manage and recover from this common digestive condition. Some people also have other symptoms, such as a loss of appetite, an upset stomach, aching limbs and headaches. The symptoms usually appear up to a day after becoming infected. They typically last less than a week, but can sometimes last longer.
