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

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 cold-smoked salmon are still possible sources of listeriosis in Sweden.