Gastroenteritis or infectious diarrhea is a medical condition from inflammation (-itis) of the gastrointestinal tract that involves both the stomach (gastro -) and the small intestine (entero -).It causes some combination of diarrhea, vomiting, and abdominal pain and cramping.iruses (particularly rotavirus) and the bacteria Escherichia coli and Campylobacter species are the primary causes of gastroenteritis. There are, however, many other infectious agents that can cause this syndrome. Non-infectious causes are seen on occasion, but they are less likely than a viral or bacterial cause.