Use of Norovirus Genotype Profiles to Differentiate Origins of Foodborne Outbreaks

EID Journal Home > Volume 16, Number 4–April 2010

Volume 16, Number 4–April 2010
Research
Use of Norovirus Genotype Profiles to Differentiate Origins of Foodborne Outbreaks
Linda Verhoef, Harry Vennema, Wilfrid van Pelt, David Lees, Hendriek Boshuizen, Kathleen Henshilwood, and Marion Koopmans, on behalf of the Food-Borne Viruses in Europe Network1
Author affiliations: National Institute for Public Health and the Environment, Bilthoven, the Netherlands (L. Verhoef, H. Vennema, W. van Pelt, H. Boshuizen, M. Koopmans); and Centre for Environment, Fisheries and Aquaculture Science, Weymouth, UK (D. Lees, K. Henshilwood)

Suggested citation for this article

Abstract
Because secondary transmission masks the connection between sources and outbreaks, estimating the proportion of foodborne norovirus infections is difficult. We studied whether norovirus genotype frequency distributions (genotype profiles) can enhance detection of the sources of foodborne outbreaks. Control measures differ substantially; therefore, differentiating this transmission mode from person-borne or food handler–borne outbreaks is of public health interest. Comparison of bivalve mollusks collected during monitoring (n = 295) and outbreak surveillance strains (n = 2,858) showed 2 distinguishable genotype profiles in 1) human feces and 2) source-contaminated food and bivalve mollusks; genotypes I.2 and I.4 were more frequently detected in foodborne outbreaks. Overall, ≈21% of all outbreaks were foodborne; further analysis showed that 25% of the outbreaks reported as food handler–associated were probably caused by source contamination of the food.

Noroviruses are members of the family Caliciviridae and recognized as major pathogens in outbreaks of gastroenteritis worldwide. Because these viruses have environmental stability (1), ability to use different transmission routes, and low infective doses (2), their source may be difficult to determine during an outbreak. Transmission can occur through contact with shedding persons; food contaminated during processing, preparation or serving; sewage-contaminated water used for consumption, cultivation or irrigation of food; contaminated aerosols resulting from vomiting; and environmental contamination (3,4). Five genogroups have been described (GI–V), subdivided into at least 40 genetic clusters (5,6).

To implement effective measures for prevention, recognition of the transmission routes is necessary. Consequently, the relative importance of different transmission routes in the total number of outbreaks is of interest for estimation of cost-effectiveness of reducing the number and size of norovirus outbreaks, particularly for geographically disseminated foodborne outbreaks. Such outbreaks are difficult to detect when the primary introduction of viruses through food occurs simultaneously in several countries or continents (7–9). Globalization of the food industry with consequential international distribution of products increases the risk for such outbreaks. For example, the first reported GII.b outbreak occurred in August 2000 during a large waterborne outbreak in southern France (10). After this outbreak, in December and January, 4 multipathogen and oyster-related outbreaks with this newly emerging genotype were reported from France. In the same period, Denmark, Finland, and the Netherlands reported norovirus cases resulting from oysters originating from a French batch that probably was sold in these countries, as well as in Sweden, Italy, and Belgium (6). All these outbreaks seemed to involve closely related and newly detected GII.b strains. After active case identification, further linked cases were detected in Germany, the United Kingdom, Spain, Slovenia, and Sweden (11,12). Another example of a geographically disseminated outbreak was several seemingly independent norovirus outbreaks in Denmark that were traced back to consumption of raspberries from Poland. Although raspberries from this contaminated batch were exported to other European countries, an alert in the Rapid Alert System for Food and Feed did not result in further linked outbreak reports (7). Thus, geographically disseminated outbreaks are sometimes identified but only after the joint and exhaustive efforts of different organizations, such as laboratory networks, food safety authorities, and public health institutions. Knowledge of the proportion of geographically disseminated foodborne outbreaks to all norovirus outbreaks will therefore provide insight into the cost-effectiveness of such efforts.

We studied whether the genotype frequency distributions (genotype profiles) of strains can be used to differentiate foodborne outbreaks related to contamination early in the food chain (i.e., during primary production) from those related to contamination later in the food chain (i.e., during preparation or serving). If so, detection of food origins likely to cause geographically disseminated outbreaks will be enhanced. We considered methods for attribution to multiple sources commonly applied to Salmonella infections (13) because different transmission routes involved in norovirus infections can disguise the foodborne origin. However, such methods require strain collections representative of noroviruses in the potential sources that are as yet unavailable because of difficulties in the direct detection of viruses in food (14–16). Therefore, we compared 2 strain collections: noroviruses identified through filter-feeding bivalve mollusk monitoring representing source contamination of food and noroviruses collected through systematic surveillance of illness in the population. The first was collected by the European Community Reference Laboratory for Monitoring Bacteriological and Viral Contamination of Bivalve Mollusks during 1995–2004 (17) and the second by the Food-Borne Viruses in Europe (FBVE) network, which has conducted surveillance for norovirus outbreaks in Europe since 1999. Prior investigation of the FBVE database of systematically collected epidemiologic and microbiological norovirus surveillance data (6) showed that the epidemiology of norovirus outbreaks in Europe varies between genogroups. An analysis of the properties of reported outbreaks indicated a clear difference between GII.4 strains and other noroviruses; non-GII.4 strains were found more frequently in outbreaks with a foodborne mode of transmission, and GII.4 strains were found more frequently in healthcare settings with person-to-person transmission (18,19). Here we demonstrate that further specification into genotypes shows additional differences in the epidemiology of norovirus outbreaks.

Suggested Citation for this Article
Verhoef L, Vennema H, van Pelt W, Lees D, Boshuizen H, Henshilwood K, et al. Use of norovirus genotype profiles to differentiate origins of foodborne outbreaks. Emerg Infect Dis [serial on the Internet]. 2010 Apr [date cited]. http://www.cdc.gov/EID/content/16/4/617.htm

DOI: 10.3201/eid1604.090723

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