Norwegian authorities found problems with the sampling plan of a company linked to a Listeria outbreak in 2022, according to a report.
In an inspection in October, the Norwegian Food Safety Authority (Mattilsynet) found that the fish producer’s sampling plan was insufficient and that environmental samples had not been taken in accordance with Troll Salmon’s internal schedule.
During the visit, the agency took 14 environmental samples and the company also carried out subsequent sampling. One of the authority’s tests came back positive, and the producer detected Listeria in two different drainage samples.
The company was ordered to take daily samples for an indefinite period of time and to update the sampling plan. It also carried out additional cleaning and disinfection of facilities and equipment, as well as work to find the source of the outbreak strain.
five sick people
The Veterinary Institute assisted the Norwegian Institute of Public Health (FHI) and the Norwegian Food Safety Authority in the investigation.
From April to October 2022, the National Institute of Public Health detected listeriosis in five people. Show dates ranged from February to October.
The cases were two women and three men aged 50 to 95 with a median age of 72. They lived in four counties: Nordland, Trøndelag, Viken and Oslo, and all were hospitalized.
After interviews with patients conducted by the Norwegian Food Safety Authority in October, smoked fish from Troll Salmon was considered a possible source of infection. Three people reported consumption of smoked salmon or trout and two named smoked salmon from this producer. Two patients were too sick to be fully interviewed, but one of them confirmed eating smoked salmon from this producer before becoming too sick.
Listeria had been found in two of the company’s smoked salmon products earlier in the year, but at a concentration below the legal limit, so they were not recalled. Items were obtained from a store in April and tested on the last day of shelf life in May 2022.
Samples were taken during the monitoring of ready-to-eat foods in stores in 2022, a program of the Norwegian Food Safety Authority. The sequences were shared with FHI, who then compared them to isolates from patients.
Possible past problems
The discovery of Listeria monocytogenes in the producer’s environmental samples coincided with the detection of the fifth case of the outbreak, and the Norwegian Food Safety Authority ordered the company to withdraw certain products from the market in October.
These isolates were later found to have a different profile from the outbreak strain, but were similar to those taken from the producer’s smoked salmon in the Norwegian Food Safety Authority’s ready-to-eat products monitoring programme, as well as well as historical isolates from patients.
Listeria monocytogenes resembling the outbreak strain were previously observed among cases in Norway from 2010, 2014 and 2018. Similar Listeria isolates were found in a sample from the Norwegian Food Safety Authority’s sliced salmon monitoring program , in producer environmental samples and patient samples from 2010 to 2015. However, the lack of epidemiological data from previous patients means that it is unclear whether or not a link exists.
No Listeria monocytogenes was found in an unopened package of Troll’s smoked salmon, taken from the refrigerator of one of the patients. Officials did not say whether the patient had eaten fish from a different package.
The discovery of Listeria in food or in production facilities is not subject to mandatory reporting in Norway, but legislation sets criteria for the amount allowed in ready-to-eat food.
The low number of cases may be because the type of sequence detected has low virulence and the concentration in food was initially low, health officials said.
No other countries that responded to a data request had cases with the same genotype as the Norwegian outbreak strain.
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