Gravad (Gravlax) and cold‐smoked salmon, still a potential source of listeriosis

Abstract

Gravad (Gravlax) and cold-smoked salmon are associated with human listeriosis in Sweden. The present investigation of Listeria monocytogenes in salmon was a follow-up of a similar study in the middle of the 1990s. Since our first study, there has been an increasing focus on food hygiene in general and specially on self-inspection and Hazard Analysis and Critical Control Points from the authorities and food producers. L. monocytogenes was isolated from 11 (three manufacturers) of the 56 products analyzed. The highest level of L. monocytogenes was 1500 cfu/g from a cold-smoked salmon product; however, the level was low (<100 cfu/g) in most products. Serovar 1/2a was predominant, followed by 4b. restriction enzyme analysis/ pulsed-field gel electrophoresis typing of the 56 salmon isolates identified five types of L. monocytogenes. One type was identical to a human type, whereas two other were closely related. These findings suggest that gravad and coldsmoked salmon are still possible sources of listeriosis in Sweden.

Human isolates ofListeria monocytogenesin Sweden during half a century (1958–2010)

“…As the present study was retrospective, the data about the sources were not supported by Swedish epidemiological investigations of outbreaks or case-control studies of sporadic cases. However, food sampling has been conducted several times in Sweden during different periods [9][10][11][12][13].…”

“…In the UK, a survey of retail cold-smoked fish found 236/1344 (17·4%) products were positive for L. monocytogenes, all samples had a level of <100 c.f.u./g [37]. The current PFGE types found in human cases of invasive listeriosis in Sweden are frequently encountered in vacuum-packed cold-smoked and gravad salmon/rainbow trout [11][12][13]. In Spain, a cluster of L. monocytogenes isolates in smoked salmon share pulsotype 1, a type recently isolated from clinical cases in Spain [38].…”

A multiple-locus variable-number tandem repeat analysis (MLVA) ofListeria monocytogenesisolated from Norwegian salmon-processing factories and from listeriosis patients

“…Listeriosis with Atlantic salmon as the food source has not been identified in Norway. In a study by Peiris et al [29] on gravad and cold-smoked salmon in Sweden, the authors conclude that the isolation of strains identical or closely related to clinical isolates, as assessed by serotyping and PFGE, suggests that these products are a possible source for listeriosis. Based on the available information from the literature and on the findings of the present study, fish should be considered as one of several possible sources of L. monocytogenes when investigating sporadic cases of foodborne listeriosis or outbreaks.…”

Effect of Fillet Thickness on Quality and Shelf Life of Gravlax Salmon

“…These products will be eaten without additional heat treatment and therefore represent a significant risk to selected consumers (young, old, pregnant and immune compromised). Examples for these foods are cold smoked and gravlax (gravid) from salmon and rainbow trout [9].…”

“…Ultra -fresh salmon is clearly important for making gravlax for both food safety reasons and to ensure the best taste and texture (quality) [10]. Gravlax products are produced by rubbing salmon fillets with a mixture of sugar, salt, pepper and covered with the herb dill and stored at refrigerated temperatures to cure for up to 2 days in plastic bags [9]. Salt in the cure acts in three ways, firstly, salt restricts the growth of some species of bacteria and extends the stability and shelf life of salmon.…”