A non-foodborne norovirus outbreak among school children during a skiing holiday, Austria, 2007.

Norovirus is increasingly recognized as a leading cause of outbreaks of foodborne disease. We report on an outbreak in Austria that reached a total of 176 cases, affecting pupils and teachers from four schools on a skiing holiday in a youth hostel in the province of Salzburg in December 2007. A questionnaire was sent to the four schools in order to obtain data from persons attending the school trip on disease status, clinical onset, duration of illness and hospitalization. A cohort study was undertaken to identify the sources of infection. The school trip attendees were interviewed by questionnaire or face-to-face on their exposure to food items from the menu provided by the hostel owner. Of the 284 school holiday-makers, 176 fitted the definition of an outbreak case (attack rate 61.9%). A total of 264 persons on the ski holiday participated in the cohort study (response rate 93%). The day-by-day food-specific analyses did not find any food items served on any of five days (December 8-12) of the holiday to be associated with infection risk. The day-specific risk analyses revealed Monday December 10 (RR: 9.04; 95% CI: 6.02-13.6; P < 0.001) and Tuesday December 11 (RR: 3.37; 95% CI: 2.56-4.43; P < 0.001) as the two most risky days for having being exposed to norovirus. According to the epidemiological investigation, airborne transmission of norovirus originating from the first vomiting case most probably initiated this outbreak; foodborne genesis was excluded. During recent years, norovirus has become increasingly established as the most important causative agent of epidemic gastroenteritis in holiday-makers all over Europe. Tourism is one of the primary industries in Austria. Timely involvement of the relevant public health authorities is essential in any outbreak of norovirus gastroenteritis, irrespective of its genesis.

A foodborne outbreak due to norovirus in Austria, 2007.

A foodborne norovirus outbreak occurred after a pre-Christmas celebration among a group of local foresters in Austria in December 2007. A total of 66 persons, 60 participants of the Christmas party and 6 kitchen staff members of the restaurant where the party took place, were identified as the at-risk cohort. Questioning of this cohort was performed by self-report questionnaires or telephone interviews (response rate of 95%). The outbreak attack rate was 33.3% (21 of 63 persons), including two of the kitchen staff. Three stool specimens yielded norovirus genogroup II. Univariate analysis revealed that exposure to a ham roll and pastry was possibly associated with risk of gastroenteritis (risk ratio [RR] of 4.45, 95% CI of 1.91 to 10. RR of 2.44, 95% CI of 0.93 to 6.39). After controlling for the effects of sex, age, and other food items with a log-linear model, ham roll remained significantly associated with disease risk (RR of 3.91, 95% CI of 1.57 to 9.76). Ham roll was most likely contaminated with norovirus during preparation by a disease-free kitchen assistant, whose infant became sick with laboratory-confirmed norovirus gastroenteritis 2 days before the party. Informing food handlers about the possible risk of food contamination with norovirus and training them in the appropriate measures of hand hygiene and environmental disinfection at the working place and at home are essential for preventing food-related norovirus outbreaks. Norovirus-infected household members of healthy food handlers must be considered a possible reservoir for foodborne norovirus outbreaks.

An outbreak of Norovirus infection affecting an Austrian nursing home and a hospital.

On November 9, 2004, a resident in a nursing home experienced a severe episode of vomiting in the dining room, in the presence of most of the other residents and members of staff. Following that episode, 17 of the 23 (73.9%) other residents and 7 of the 18 (38.9%) staff members fell ill with diarrhea and/or vomiting in the period up to November 17. A second cluster of gastroenteritis occurred between November 11 and 28, 2004, in a nearby hospital to which eight cases among the nursing home residents had been referred. Ten of 46 (21.7%) other hospital patients and 18 of 60 (30%) members of the hospital staff suffered from vomiting or diarrhea. Epidemiological and laboratory investigations proved a causal relationship between the two institutional clusters of short-lived gastroenteritis related by time and place, and identified Norovirus genotype GGII.4 (Jamboree-like) as the causative pathogen. Control measures for Norovirus, based on epidemiological and clinical features of the outbreak, were effectively implemented in the nursing home without waiting for virological confirmation. At the hospital, specific measures were not implemented until after virological confirmation of the causative agent, by which time 16 cases had already occurred. In a suspected Norovirus outbreak it is of great importance -- especially within closed and semiclosed settings -- to implement control measures as soon as possible, even before laboratory confirmation of the agent.