Listeria outbreak: the importance of traceability in food safety and prevention

More than 150 cases of listeriosis occurred in Spain in Summer 2019 due to the consumption of contaminated meat. The meat producer sold contaminated meat to a second company, which sold it without indicating the name of the producing company on the label. This has led to the widespread of listeriosis as the origin of the meat could not be determined readily by the authorities.

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What turned an outbreak like this into a public health problem was not only the contamination but the gap in the record. Article 18 of Regulation (EC) No 178/2002 requires every food business to know its immediate supplier and its immediate customer, the principle usually described as one step back and one step forward. The chain works only if each link keeps its own record: when one operator resells material without carrying the producer's identity forward, the trail stops there, and the authorities have to reconstruct by sampling what should have been readable from documents.

Listeria monocytogenes makes that delay expensive. The interval between eating contaminated food and falling ill can run to several weeks, so by the time a cluster of cases is recognized the implicated batch may already have been eaten, discarded or distributed much further. Ready-to-eat foods are the products of concern precisely because no cooking step is left to correct the problem, which is why Regulation (EC) No 2073/2005 sets microbiological criteria for that category.

The laboratory contribution to this is of two kinds. Detection answers whether a named organism is present in a sample, and it is the routine question a producer asks of a product or of a production environment. Characterizing isolates so that cases in different places can be linked to a single source is a separate, sequencing-based exercise, and in an outbreak it is carried out by the public health laboratories that hold the clinical isolates.

Our own work sits on the first of those, and beside it the identity questions that traceability records are meant to answer: what species a raw material really is, whether a batch matches its specification, whether an undeclared ingredient is present. We report the result and the method; the decisions about a batch, a supplier or a notification belong to the operator who placed the food on the market.