Health officials observed an increased incidence of gastroenteritis in Yuma, Arizona, June 2007. Laboratory testing isolated Salmonella Heidelberg in stool samples of case-patients. These isolates were compared using pulse-field gel electrophoresis and found to be indistinguishable. Further investigation probed the source of the outbreak. By comparing food histories, the health department workers determined the source to be a fast food restaurant chain. No specific food was implicated, and environmental swabs of cutting boards were positive for Salmonella, leading the investigators to conclude cross-contamination was the cause of the contamination.