Acute diarrheal illness can be defined as the sudden onset of the passage of a greater number of stools than usual that show a decrease in form.

It is gener­ally accompanied by other clinical symptoms such as fecal urgency, tenesmus, abdominal cramps, pain, nausea, and vomiting. In most cases the symptom complex is a result of intestinal infection by a viral, bacterial, or parasitic enteropathogen; occasionally it is secondary to ingestion of a microbial exotoxin.