Outbreak of norovirus infection among river rafters associated with packaged delicatessen meat, Grand Canyon, 2005

Background. Norovirus is often transmitted by infected food handlers at the point of service, whereas reports of food contamination before wholesale distribution are rare. In September 2005, we investigated reports of gastroenteritis among rafters who went on unrelated trips on the Colorado River. Methods. We surveyed all companies that launched rafting trips during the period from 14 August through 19 September 2005 to identify trips in which ≥3 rafters became ill. We conducted a case-control study. Case patients were persons who experienced diarrhea or vomiting that commenced ≤72 h after the trip launch; control subjects were persons who did not become ill ≤72 h after launch. We tested stool samples and food specimens for norovirus. We performed a traceback investigation of the suspected food vehicle and inspected the implicated processing plant. Results. Three or more rafters developed gastroenteritis during 13 (14%) of 91 trips, for a total of 137 ill persons. Of the 57 case patients who became ill ≤72 h after trip launch, 55 (96%) reported eating delicatessen meat, compared with 75 (79%) of 95 control subjects (odds ratio, 7.3; 95% confidence interval, 1.7-66.7). All delicatessen meat eaten by case patients came from 1 batch purchased from 1 processing plant and had been sliced, vacuum-packed, and frozen (temperature, -23°C) for 7-28 days. An employee sliced this batch with bare hands 1 day after recovery from gastroenteritis. Identical norovirus sequences were identified in stool specimens obtained from rafters on 3 different trips; 2 of 5 meat packages also tested positive for norovirus by reverse-transcriptase polymerase chain reaction and DNA hybridization. Conclusions. Food handlers can contaminate ready-to-eat meats with norovirus during processing. Meatprocessing practices should include specific measures to prevent contamination with enteric viruses and subsequent widespread outbreaks.