Final Report

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Date:

17/02/2005

Summary

The work described in this overview shows that food- and waterborne transmission play an important role in the spread of norovirus (NoV, previously named Norwalk-like viruses) throughout Europe. NoV are ubiquitous, highly contagious, cause large international outbreaks of gastro-enteritis. This is of concern: current quality control for food and water in Europe measures bacterial contamination, and does not monitor viral contamination. Therefore, food can pass microbiological quality control, but still contain viruses. Matched with the virtual absence of a surveillance system for detection of common-source outbreaks of illness due to enteric viruses, this highlights a weak spot in European infectious disease control. The NoV in fact serve as sentinels: when present, common-source outbreaks will relatively easily be detected due to the high attack rate and short incubation period. More insidious, however, are the enteroviruses and fecally-transmitted hepatitis viruses with a high proportion of asymptomatic infection after an incubation period of up to 2 months. These viruses cause illnesses like hepatitis (hepatitis A and E viruses) and infections of the central nervous system (enteroviruses). Signaling common source outbreaks with these viruses is virtually impossible without a strong (molecular) laboratory component to underpin the epidemiological investigations, aided by international exchange of laboratory data. This should be developed to better be prepared at the European level.

The data sharing across Europe has revealed numerous examples of seemingly localized viral disease outbreaks, which may impact on the epidemiology of these viruses in other countries. Outbreaks of water-borne or food-borne diseases in popular tourist resorts have been detected. Often, the true extend of such outbreaks remains a mystery, but is likely to be far greater than what has been detected through routine surveillance. We have seen examples of virus shift and drift, both mechanisms that are known to enhance the diversity of viruses. These examples are worrisome, in that the conditions are favorable for their generation: some of the foods that were examined in our project were contaminated with multiple variants. The experimental design to create a novel virus would be to simultaneously infect a susceptible host with 2 or more related viruses. While we can not exactly pinpoint the moment of generation of the variants that we detected, it is a very likely hypothesis that they are a result of food-borne or water-borne exposure.

A way out of this dilemma might be to develop guidelines for microbial food safety that include viral contaminants. Sofar, that is not the case, and there is increasing evidence that viruses slip through the mazes of the control web for food quality. That implies that – in the HACCP analysis, knowledge on behavior of viruses needs to be included, that food handlers should specifically be educated to reduce the likelihood of contamination for all pathogens, and that guidelines should be drafted that reliably indicate the presence of absence of viruses. That is easier said than done: the screening of food samples – with the exception of oysters- is in its infancy stages. Given the nature of viral contamination (very low dose, periodic) it will be difficult if not impossible to develop methods that are both reliable AND practical. Therefore, bridging the gap between food quality control and public health surveillance may be needed, and research to provide some data on the predictive value of outbreak investigations for detection of food contamination. This should include the role of virus typing and data sharing. Data are also needed on effective prevention strategies for food-borne contamination, and – as part of the missing data- stability of different food-borne viruses in different environmental circumstances, products, and processing methods.

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