Acute diarrhea is usually defined as increased volume or looser consistency of stool. Specifically, more than 3 loose stools daily for less than 14 days. The majority of cases are self-limited. There are typically 4 causes for acute infectious diarrhea: noroviruses, diarrheogenic E coli, Clostridium difficile, or other toxins or parasites. Diagnosis and treatment of specific causes are reviewed.