Salmonella is a bacterium that is the second most frequent cause of foodborne illness in Europe - estimated to be over 100,000 cases a year (and 1.2 million cases a year in the US). Salmonellosis can result in hospitalization and, in about 0.04% of cases – death.
Humans are exposed to Salmonella from several sources – fecally-contaminated meat from chickens, turkeys, ducks, pigs, and cows being the most important, as well as eggs.
Salmonella is a very hardy bacterium, so it can contaminate vegetables fertilized with manure, and can be present in rivers and lakes in which people swim from runoff from fields. It can also grow in normal environmental conditions.
This makes it extremely difficult to pinpoint the original source of the bacteria. However, Salmonella can be identified as belonging to a specific sero- or phage-type, of which there are many. Moreover, the proportions of these sero-and phage-types are very different among the various animal species.
As a result, it is possible to match the typing patterns of these bacteria in human cases of illness with the typing patterns in animals. This was first demonstrated in an academic paper we co-authored.
The European Food Safety Authority (EFSA) commissioned us, after a tendering process, to produce an attribution assessment that would identify the main sources of Salmonella by food type and country. The problem was made more complex by the widespread and unregulated movement of animal products between Member States.
Vose produced a Markov Chain Monte Carlo model using the OpenBugs software. The model was able to normalize to the data set for one year and accurately predict the illness patterns for the following year, giving us a good level of confidence in its robustness. The model provided EFSA’s expert panel with all the answers they required.
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