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.

Food safety challenges and One Health within Europe

“…Among these products, non-heat-treated raspberries are a common source of outbreaks, as reported, e.g. in Norway [ 37 ], France [ 38 ], Sweden [ 39 , 40 ], Denmark [ 41 ] and Finland [ 42 ]. One driver for this is the growing trend for eating healthy and minimally processed food, including increased consumption of, e.g.…”

Microbiological Parameters in the Primary Production of Berries: A Pilot Study

“…Outbreaks of foodborne illness due to the consumption of fresh produce contaminated with human pathogens are increasing, probably linked to the fact that these products are usually consumed raw [ 5 , 6 , 7 , 8 ]. Berries were responsible for foodborne outbreaks due to virus contamination, including as frozen fruits [ 9 , 10 , 11 ]; frozen raspberries have been reported in previous studies as contaminated produce responsible for Norovirus outbreaks in Europe [ 12 , 13 , 14 ]. Other important outbreaks highlighted that frozen berries are an efficient vehicle of enteric virus infection, as in the case of the multi-country outbreaks of Hepatitis A Virus (HAV) reported in 2013 [ 15 ].…”

Public health investigation and response to a hepatitis A outbreak from imported scallops consumed raw—Hawaii, 2016

“…This approximation helped guide the next steps in the response and investigation and was one of several key pieces of information that helped implicate the contaminated product. While others [33][34][35][36][37][38][39] have utilised an online survey to rapidly disseminate questionnaires to identified cohorts or a pre-registered body of controls, it has not been previously published as a means to rapidly estimate locality-specific baseline exposure rates. The ability to generate a rapid approximation of local baseline exposures may be critical in determining a suspect source during an outbreak.…”