Eurosurveillance - Volume 13, Issue 44, 30 October 2008

In this week’s issue of Eurosurveillance, four European countries present recent outbreaks of Salmonella Typhimurium. The articles present a variety of innovative outbreak investigation methods, in particular molecular subtyping which permits to compare strains within and between countries.

An increased number of Salmonella Typhimurium cases were reported in Switzerland between May and June 2008. Investigations involved 72 cases. Results of PFGE typing identified several outbreak strains, the dominating one present in 43 of the 72 isolates. Strains affecting one third of the cases were also found in animal samples, in particular pork. However, no specific food source could be identified. Outbreaks described in this paper highlight the importance of food safety regulations such as those on minced meat and meat preparations issued by the European Commission and adopted by Switzerland into the national law.

An unusually high number of cases of Salmonella Typhimurium was reported in France in June 2008. In the course of epidemiological investigations 112 cases were ascertained, of whom 75 were interviewed. Subtyping by PFGE and MLVA identified a strain named ""majority profile"". Subtyping results were available for 45 interviewed cases, 30 of whom (majority below 15 years of age) were found to be infected with the majority profile strain. Evidence suggested the occurrence of an outbreak due to a monoclonal S. Typhimurium strain with the single PFGE profile XTYM-50. Cases with identical PFGE profile were also detected in Switzerland but no link with outbreaks occurring in the same period in Denmark and in the Netherlands was found. Contamination of a product distributed nationally was suggested as the cause of the outbreak but investigations did not reveal any specific food source.

An outbreak of Salmonella Typhimurium phage type U292 has been ongoing in Denmark since 1 April, with 1,054 cases registered until 23 October 2008. Extensive investigations including hypothesis-generating interviews, matched case-control studies, cohort studies in embedded outbreaks, shopping list analyses, analyses of food samples from patient's homes, trace-back analyses and extensive microbiological analysis of products have not provided clear indications of a specific source of infection but the main hypothesis is that the vehicle of the outbreak are different pork products. In addition to the large U292 outbreak, at least four other S. Typhimurium outbreaks (caused by phage types U288, DT120, DT3 and DT135) have been investigated in Denmark in 2008.

A large, countrywide outbreak due to multi-resistant Salmonella Typhimurium phage type DT104 is ongoing in the Netherlands, with 152 cases as of 20 October. Pilot interviews did not suggest any specific source of infection but a hypothesis pointing to pork products has been formulated and a large case-control study is under way. Earlier this year two other oubtreaks due to S. Typhimurium were detected and investigated, the first (DT15A) linked to a particular brand of cream cheese, the other (Dutch phage type ft507) to a local butcher.

Between mid-September and 19 October 2008, nine clusters of norovirus infection involving around 90 primary cases and over a hundred secondary cases were identified in patients from the Netherlands, Ireland, Italy and France, linked to pilgrimage to Lourdes, France.

This paper reflects on the qualitative risk analysis framework developed for a Foresight study on the Detection and Identification of Infectious Diseases, which was coordinated in 2005 by the United Kingdom (UK) under what is now the Government Office for Science, Department for Innovation, Universities and Skills. The risk assessment covered human, plant and animal diseases in the UK and Africa in the years 2015 and 2030. Through engaging a diverse pool of experts, we developed a model conceptualising disease spread as the outcome of interactions among sources, pathways and drivers. We then used this model to conduct a Delphi survey of experts. The factors perceived most likely to contribute to infectious disease spread in 2015 and 2030 included geographic extension of existing pathogens (partially due to climate change), over-use of antibiotics/antivirals/pesticides leading to drug resistance, and zoonoses. Our methodology provides a framework for those who need to integrate a wide range of perspectives and factors into their planning and analyses.