Gastroenteritis is inflammation of the stomach or bowels that is caused by an infection. Certain bacteria or viruses may also produce poisons called toxins that can irritate your gut and cause it to produce excess fluid. This can cause the symptoms of gastroenteritis, e. g diarrhea. It's more common in babies and young children who may have it more than once in a year. If you have gastroenteritis, it usually goes without you needing medical treatment. If a baby or a young child has gastroenteritis it can be more dangerous because she/he becomes dehydrated more easily.
Attribution: BUPA