A total of 20 people have been sickened from September 2013 but 15 cases occurred in June, July and August.
The first person died on 13 September and the latest recorded death was on 9 August.
The type of sausage, known as ‘Rullepoelse’ was traced back to Jørn A. Rullepølser in Hedehusene, which was shut this week and a full withdrawal of the company's products, which includes meats products and sausages was launched.
Jørn A. Roll Sausages has delivered products to other companies and the Food Administration is working to find full information.
‘Rullepoelse’ is typically flattened pork belly with spices and herbs, rolled up, sliced and served cold.
More cases expected
Statens Serum Institut (SSI), the National Health Agency, said it is investigating eight more cases and using whole genome sequencing (WGS) on four isolates with results expected shortly.
SSI is working with the Danish Food and Drug Administration and the Technical University of Denmark.
Steen Ethelberg, from SSI, said the WGS demonstrated that the patients were infected with the same strain of Listeria.
“We had the first case in April and two in June when we realised there was an outbreak with more diagnosed in June, July and August,” he told FoodQualityNews.com.
“We are monitoring the case situation and doing whole genome sequencing on isolates we have and we will do that on the new isolates to see if the other cases are positive for the outbreak strain and if isolates from the sausage test positive.
“We think the outbreak is under control but we expect more cases because of the long incubation period of Listeria.”
Ethelberg said the distribution of products appeared to be just inside Denmark with no exports.
Underlying health problems
The patients affected are 11 women and nine men aged 43-89 years with the deaths reported within 30 days of the test date.
Authorities said patients who died also had serious underlying health problems and deaths cannot be reliably attributed to Listeria infection.
The Danish Food and Drug Administration was informed by SSI of the possibility of a Listeria outbreak in June.
After investigations to Jørn A. Rullepølser was identified as the main source of infection.
Since 2006, the number of sufferers of Listeria has been between 50 and 60 per year with the highest in 2009, when almost 100 were sick.