Gastroenteritis (or acute diarrhoeal disease) is an acute infection of the bowel resulting in watery diarrhoea without visible blood or mucus in the stool. It is caused by a wide range of organisms which interfere with the normal functioning of the cells that line the bowel wall, resulting in loss of water and electrolytes into the stool. It is the commonest form of diarrhoea in childhood. Vomiting and abdominal cramps in older children are common with gastroenteritis but pyrexia is absent or only mild.

Gastroenteritis is usually caused by Rota virus or E. coli. Rota virus is highly infectious and seen in both poor and wealthy communities especially in children less than 1 year old. The infection is usually spread from the stool of the infected person by unwashed hands or contaminated water or food (the faecal–oral route). Poor hygiene or sanitation may result in outbreaks of gastroenteritis. Gastroenteritis usually presents as acute diarrhoea. However, if the bowel mucosa is damaged by the infection, gastroenteritis may also result in persistent diarrhoea.