Thirteen people were part of a Listeria outbreak after eating liver pâté in Austria at the end of this past year and one person died.

The outbreak strain had not been detected previously in Austria but no linked cases were found after an international alert, according to a report published in the journal Eurosurveillance.

In Austria, notification of invasive listeriosis infections are mandatory. The Austrian National Reference Laboratory for Listeria (NRL) is responsible for whole genome sequence (WGS)-based typing of all isolates.

Outbreak investigation
In late December 2018, the local health authority of Styria and the NRL confirmed an outbreak of febrile gastroenteritis, including one case of culture-confirmed Listeria monocytogenes bacteremia, among 32 people at a tavern in mid-December as part of a celebration. They had consumed mixed platters with several meat products and pâtés originating from an unnamed local production facility.

At the end of January this year, the Austrian Ministry of Health imposed a mandate on the Austrian Agency of Health and Food Safety (AGES) to investigate the outbreak to identify the causative agent and likely source of infections, to detect and prevent further cases. The delay was due to closure of the tavern over the Christmas period.

Information from the local food authority on those involved restricted the incident to one local meat producer and three grocery shops. Items from this producer were offered at six locations, including the affected tavern and sold directly from the factory.

Of 19 stool specimens from people with febrile gastroenteritis, 10 were positive for Listeria monocytogenes.

A total of 73 food and environmental samples were analyzed for Listeria monocytogenes with two food and one environmental sample positive. The food samples, smoked meat (Geselchtes) and liver pâté (Leberstreichwurst) were collected at the tavern. It was learned that they were produced by the same company. A gully water sample from January 2019 by Styrian health authorities at the production facility of this company also tested positive.

One death recorded
Active case finding identified two more people with invasive listeriosis. They lived in the same two geographical districts as the tavern and production company.

The first isolate was from a person in their early 80s who had not visited the tavern but developed symptoms in November 2018. This person, who died from the infection, had repeated consumption of liver pâté from the production company that was bought at a local market.

The second isolate was from a case in their mid-50s with endophthalmitis, with onset of clinical symptoms in December 2018 but this person had not visited the tavern. They had regular consumption of liver pâté so it is possible this may have been produced at the implicated company.

In total, seven females and six males aged 4 to 84 years old living within 24 kilometers of Styria, were confirmed as outbreak cases.

After the outbreak was confirmed in December, cleaning of the tavern and at the production  company was done by sanitation firms, under supervision of the local health authority. Only heat-treated products could be sold until Listeria monocytogenes was not detected after repeated sampling. No more illnesses were found by the end of December and the outbreak was declared over.

Use of epidemiological data and WGS-based typing confirmed the local outbreak due to a Listeria monocytogenes IVb-CC4-ST4-CT7652 strain, not previously detected in Austria or anywhere else.

A tavern offers a limited selection of traditional food, especially local meat products and cheese, in a buffet-like manner but has a functioning kitchen including fridge and freezer.

The researchers said it was possible that the time between food preparation and service might have been long, increasing the possibility for Listeria to multiply.

Traditional Austrian meat products such as liver pâté and jellied pork do not need heating prior to consumption and have been identified as potential risky food due to growth potential for Listeria.

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