Listeria in Polish salmon likely from environmental contamination

A listeriosis outbreak from contaminated salmon earlier this year has been identified as a probable case of environmental contamination, according to experts.

The implicated salmon was processed in Poland and sold primarily in Denmark, and Listeria monocytogenes from the same isolate as the Danish outbreak was later found at a French retailer. Genetically linked isolates were also reported in Germany in late November, reports Food Quality News.

Investigators said that because the salmon products associated with each location came from different batches, it was likely that environmental contamination took place at a common processing plant.

What is environmental contamination?

To someone outside the food industry, “environmental contamination” might conjure images of polluted waters or smoggy air. But in a food processing plant, environmental contamination is what happens when pathogenic bacteria in the food production facility enter a food product.

Pathogens can enter an environment by many means: from foot traffic, through drains, or due to cross-contamination from one ingredient to others, to name just a few ways.

Once a pathogen has been detected, many steps must be taken to protect a business and its consumers from future complications. In the case of the Danish and French L. monocytogenes outbreaks, like many other cases, this required quick thinking with outbreak control measures that involved first identifying a contamination source.

“Experiences from previous investigations suggest that once L. monocytogenes is detected in one product, the whole production site should be subject to a thorough inspection, and sampling with special attention to all the possible contamination/cross-contamination issues before implementing corrective measures,” said outbreak investigators.

Pathogen detection

Food processors and producers can detect pathogens thanks to their environmental monitoring programs. These are self-designed programs used to prevent outbreaks and product recalls by finding pathogens before products are sent off to hit retail shelves. This involves regularly testing the facility for the presence of pathogens.

After an outbreak happens, pathogen detection technology is essential for monitoring the facility in case the bacteria linger, including in the salmon Listeria situation.

“The risk for L. monocytogenes strains in the production environment requires the close monitoring for several years to ensure the elimination of these,” investigators said.

Food processors test equipment, machinery, surfaces, drains and all other aspects of the processing environment for pathogens according to a regular schedule. Traditionally, this involves taking samples, putting them in a bacteria-cultivating medium and seeing if bacteria grows. However, new technology that targets the ribosomal RNA of some types of bacteria allows testing to happen much more quickly without the need to grow pathogens within a facility. This reduces risks for companies and for consumers, because potential contamination and other problems can be discovered before becoming serious.

For more information on Neogen’s test that targets Listeria without enrichment in under an hour, click here.

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