an epidemic, highly communicable but rather mild disease of sudden onset, caused by the epidemic gastroenteritis virus (especially Norwalk agent), with an incubation period of 16-48 hours and a duration of 1-2 days, which affects all age groups; infection is associated with some fever, abdominal cramps, nausea, vomiting, diarrhea, and headache, one or another of which may be predominant. SYN: acute infectious nonbacterial gastroenteritis.