Several University of Colorado students from one sorority became ill with symptoms of bloody diarrhea and cramping. Additional illnesses were reported. E. coli O157:NM(H-) was determined to be the cause. Consumption of alfalfa sprouts at the Jimmy John's Restaurants in Boulder County and Adams County were risk factors for illness. In addition, the environmental investigation identified Boulder Jimmy John's food handlers who were infected with E. coli and who had worked while ill. The health department investigation found a number of critical food handling violations, including inadequate handwashing. The fourteen isolates from confirmed cases were a genetic match to one another.