Date: Thu 25 Oct 2018
Source: European Centre for Disease Prevention and Control (ECDC) [edited]
Ready-to-eat salmon products, such as cold-smoked and marinated salmon, are the likely source of an outbreak of listeriosis that has affected Denmark, Germany, and France since 2015. 12 cases, including 4 deaths, matched the outbreak strain identified by whole genome sequencing (WGS). A previous investigation and new WGS findings suggests a common source of contamination, states the latest report by ECDC and the European Food and Safety Authority (EFSA).
WGS-based analysis identified 12 patients with onset of symptoms between October 2015 and May 2018: 6 in Denmark, 1 in France, and 5 in Germany. The 1st cluster of cases reported by Denmark in September 2017 was linked to the consumption of salmon products produced in Poland.
Initial investigations suggested that contamination may have taken place at a Polish processing company but the lack of recent WGS data on the _Listeria monocytogenes_-isolates collected at the processing plant make it impossible to confirm this is the case.
Although control measures were implemented following the Danish outbreak investigation in September 2017, the same strain was found in a salmon product in France in October 2017 and in a patient in Germany in May 2018. This suggests that the source of contamination may still be active and that contaminated products may have been distributed to more EU countries. Until the source of contamination is identified and controlled, new invasive _L. monocytogenes_ infections associated with this outbreak may still occur.
It is likely that the extent of the outbreak is underestimated, since the use of sequencing to characterise _L. monocytogenes_ isolates is only used by a few EU countries. A recent EU-wide study coordinated by ECDC revealed that more than half of the severe listeriosis cases in the European Union belong to clusters, many of which are not being picked up fast enough by the current surveillance system.
Listeriosis is a relatively rare but potentially severe food-borne disease that has been reported in increasing numbers in the EU/EEA countries since 2008. In 2016, 2536 cases were reported, including 247 deaths. Pregnant women, the elderly and immunocompromised people are at higher risk of contracting listeriosis.
[Refrigerated smoked salmon is a recognized potential source for listeriosis, similar to other cold cut meats and non-heat treated cured smoked meats, being a ready-to-eat product, that is, does not require further cooking before eating. The ECDC report said that more cases related to this outbreak are expected, despite a recall in 2017 by the Salling Group (formerly Dansk Supermarked Group/DSG) of cold-packed smoked salmon manufactured in Poland from 600 stores in Denmark and a limited number in Metro Poland, after the outbreak strain of _Listeria monocytogenes_ was identified in the product (see ProMED-mail post Listeriosis - Denmark, Poland: smoked salmon, recall http://promedmail.org/post/20170902.5290728)
. Salling Group consists of chains (fotex, Bilka, Netto, and Salling) with more than 1400 stores in Denmark, Germany, Poland, and Sweden. - ProMED Mod.ML]
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