Investigations

In both the Danish and the Dutch outbreaks reported in this issue, investigation by the local and national authorities was sufficient to identify the food vehicles, without pooling epidemiological information across nations. However, in some dispersed outbreaks, it is necessary to combine data across multiple jurisdictions to identify the food vehicle. This can mean that a standard epidemiological approach is needed, requiring substantial coordination. Identifying the lead hypotheses, devising a single questionnaire to gather the critical data from cases and controls, and conducting a rapid statistical analysis can again require active collaboration to gather sufficient information to implicate a specific food.

The main objectives of an investigation are to prevent further cases by an immediate intervention (e.g. by halting distribution of a food or by recalling it from commerce) and by a longer term prevention effort to identify processes or practices that need to be changed to avoid future incidents of contamination [Reference Lasky10]. For immediate intervention it is necessary to identify the vehicle of infection, while prevention of future outbreaks requires identification of the source. That means investigating the chain of production sufficiently well to determine how contamination was likely to have occurred.

These outbreaks illustrate why it is essential to tackle the problem at the production and processing plant. Testing a lot of food and destroying the batch that tested positive served as an immediate intervention, but did not prevent the subsequent outbreaks in Denmark and The Netherlands. The key issue here is that whatever the initial control measures that were instituted at the processing facility in the third country were, they were apparently not sufficient, therefore another batch of contaminated meat arrived and caused illness.

In principle, the search for the cause of an outbreak is focused on identifying one food vehicle. These two reports and others [Reference Koch11] are good examples of outbreaks in which different brands or foods can have one single source of contamination.

Communication

During the investigation of foodborne outbreaks, the close collaboration between public health and food safety authorities is pivotal, but achieving this communication is often a challenge even within one country. For multi-national outbreaks this task is even more complex when the contaminated food is traced to a country that may not have recognized any related illnesses and has not previously been involved in the investigation, as was the case in the two outbreaks reported here. Within the United States, such communication occurs rapidly and informally through collegial contacts among neighbouring states, through the electronic networks of PulseNet and OutbreakNet, through formal liaison arrangements between the CDC, the US Department of Agriculture, and the Food and Drug Administration, through the Epi-X rapid notification system, and through the Morbidity and Mortality Weekly Report. In Europe, there are several established means for rapid international exchange of information about foodborne outbreaks. There is the informal exchange of information between public health foodborne disease specialists as established in Enter-net [Reference Fisher and Threlfall4], the more formal exchange including the Early Warning and Response System (EWRS) [12], rapid communication of first results in Eurosurveillance Weekly [Reference Ethelberg13] and the Rapid Alert System on Food and Feed (RASFF) of the EU Commission [14]. The Danish colleagues used all of these channels to communicate the outbreak, although the actual extent of communication is not explained in detail. It was not made clear whether and how communication was established with the authorities responsible for the production plant and what measures were taken there after the Danish outbreak. It will be crucial to optimize the performance and use of these communication systems as two-way channels in the future.

This pair of reports is a good illustration of why a surveillance network is needed at the European level, why joint investigations are desirable, and why definitive action at the source is imperative for the prevention of future outbreaks. The national authorities remain in charge of establishing the measures to achieve these ends, and of monitoring their effectiveness. Close and timely cooperation between human public health and food safety authorities at the European level, between ECDC and the European Food Safety Authority (EFSA), could enhance such investigations. The added value of a cooperative network would include coordinating multi-national investigations, supporting countries in their investigations upon request, establishing the scientific basis for interventions, providing timely information about events by providing a communication platform and a database with timely reporting and analysis of relevant variables, and developing proposals for a standardized epidemiological approach to investigations.