Listeria monocytogenes i vakuumförpackad lax :

Sammanfattning: Listeriosis, which is caused by Listeria monocytogenes, is a rare food borne disease that primarily affects people whose immune system is weakened. These may be elderly people, pregnant women, new-born infants and individuals on immunosuppressive medication. The most common symptoms are meningitis, septikemia and abortion. The mortality is high, on average 20-30 %. In recent years the number of cases in Sweden has increased. This increase is especially pronounced in south of Sweden, in the province of Skåne. In 1997 there was an outbreak of listeriosis in Värmland in Sweden, due to consumption of vacuum-packaged cold-smoked and gravad rainbow trout. Thus, such products were analysed for Listeria monocytogenes. The starting point for the present study was the hypothesis that the increase of listeriosis in Skåne may be due to the consumption of vacuum-packaged salmon and rainbow trout. Raw fish is not thought to be an important source of contamination, but the fish is contaminated with L. monocytogenes in the production plant. Contamination most likely occurs during the preparation, principally during the brining process, in the factory. Since the gravad and cold smoked fish is not supposed to be heated before eating there is no step in which the bacteria will be eliminated. The National Food Administration conducted a large investigation on L. monocytogenes in ready-to-eat products in Sweden during 2001. They found, for example, that 7% of the samples of vacuum-packaged smoked and gravad fish were positive for these bacteria. In the present study 39 samples of vacuum-packaged cold smoked and gravad salmon and rainbow trout are included. Of those, 35 were bought in Skåne. Ten of the samples were positive for L. monocytogenes. The quantitative analysis showed that the number of L. monocytogenes in two of the samples (2000 and 4000 CFU/gram, respectively) by far exceeded the limit of 100 CFU/gram set up by the National Food Administration. Isolates from the positive samples were cleaved with restriction enzymes (REA) and analysed with Pulsed-Field Gel Electrophoresis (PFGE). All of the clonal types found in the samples have previously been isolated from humans suffering from listeriosis. The only serogroup found in the fish was 1/2. It is concluded that vacuum-packaged ready-to-eat fish products may be an important source of listeriosis in human.