title: Non-heat-treated frozen raspberries the most likely vehicle of a norovirus outbreak in Oslo, Norway, November 2013.
abstract: In November 2013, the Norwegian Institute of Public Health was notified of a gastroenteritis outbreak following two meetings held at a conference centre. Identical food and beverages were served during the meetings. We investigated in order to identify the vehicle of infection and implement control measures. Meeting participants completed an online questionnaire on consumption of foods and beverages. We asked symptomatic participants to provide a stool sample. We defined a case as diarrhoea and/or vomiting in a participant who became ill within 3 days after the meeting. We calculated attack rates (AR) and adjusted risk ratios (aRR) with 95% confidence intervals (CI) using binomial regression. We conducted environmental investigations. Overall, 147/168 (88%) participants responded, of which 74 (50%) met the case definition. All five stool samples provided were norovirus positive. No kitchen staff reported being sick. Risk of illness was higher in those who consumed raspberry mousse (aRR 3·4, 95% CI 1·4-8·2) and sliced fresh fruit (aRR 1·9, 95% CI 1·3-2·8). Seventy cases (95%) ate raspberry mousse. Frozen raspberries used for the mousse were imported and not heat-treated before consumption. Non-heat-treated frozen raspberries were the most likely outbreak vehicle. Contamination by a food handler could not be excluded. We recommend heat-treatment of imported frozen berries before consumption.
authors.affiliation: Department of Infectious Disease Epidemiology,Norwegian Institute of Public Health,Oslo,Norway.
authors.forename: M
authors.identifier: 0000-0002-9952-2153
authors.initials: M
authors.lastname: Einöder-Moreno
authors.affiliation: Department of Infectious Disease Epidemiology,Norwegian Institute of Public Health,Oslo,Norway.
authors.forename: H
authors.initials: H
authors.lastname: Lange
authors.affiliation: Department of Public Health,Health Agency,Municipality of Oslo,Oslo,Norway.
authors.forename: M
authors.initials: M
authors.lastname: Grepp
authors.affiliation: Norwegian Food Safety Authority,Oslo,Norway.
authors.forename: E
authors.initials: E
authors.lastname: Osborg
authors.affiliation: Department of Virology,Norwegian Institute of Public Health,Oslo,Norway.
authors.forename: K
authors.initials: K
authors.lastname: Vainio
authors.affiliation: Department of Infectious Disease Epidemiology,Norwegian Institute of Public Health,Oslo,Norway.
authors.forename: L
authors.initials: L
authors.lastname: Vold
mesh_terms: D000328:Adult; D000368:Aged; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000821:virology; D015331:Cohort Studies; D004196:Disease Outbreaks; D005260:Female; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000453:epidemiology* / Q000821:virology; D005628:Frozen Foods / Q000821:virology*; D005759:Gastroenteritis / Q000453:epidemiology* / Q000821:virology; D006801:Humans; D008297:Male; D008875:Middle Aged; D029322:Norovirus / Q000502:physiology; D009664:Norway / Q000453:epidemiology; D012189:Retrospective Studies; D065856:Rubus / Q000821:virology*; D055815:Young Adult
keywords: Berries; Caliciviridae infections; disease outbreaks; foodborne diseases; norovirus