[Frozen berries as a risk factor for outbreaks of norovirus gastroenteritis. Results of an outbreak investigation in the summer of 2005 in Hamburg].

An outbreak of acute gastroenteritis occurred in Hamburg among guests of a canteen in August 2005. A total of 241 persons were found ill. In stool samples of 16 of them Norovirus Genogroup I was identified. Neither bacterial nor viral pathogens could be detected in food samples. Among 162 guests enrolled in a cohort study, 69 (42.6 %) met the case definition. A desert dish made from blackberries and yoghurt showed a significant association with the disease (RR 6.9; 95% CI 3.36-14.16). In addition, a protective effect of the decision for the alternative desert dish ice cream was observed (RR 0.9; 95% CI 0.08-0.45). The desert, which was prepared in the canteen kitchen from yoghurt and frozen blackberries, was the most likely source of the outbreak. Frozen berries should be included in the HACCP concepts for canteen kitchens.