Norwalk virus outbreak at a college campus.

An epidemic of nonbacterial gastroenteritis affected nearly 100 students at a college campus in Jefferson County, Alabama. The outbreak closely resembled food poisoning, since there was a rapid occurrence of multiple cases within a short period. Vomiting occurred in 79% and diarrhea in 64%; fever was uncommon. We found a significant association between the illness and the eating of lettuce at a meal one day before the outbreak began. Paired serologic specimens showed evidence of Norwalk virus infection. Twenty acutely ill students had leukocytosis (mean WBC 12,780/cu mm) and lymphopenia--a pattern that may be characteristic of Norwalk virus gastroenteritis. Outbreaks of Norwalk virus infection as well as other nonbacterial gastroenteritis may closely mimic epidemics caused by more familiar foodborne pathogens such as staphylococci.