Danish officials have solved a Listeria outbreak linked to hummus that first affected people in 2016.
Statens Serum Institut (SSI), Fødevarestyrelsen (Danish Veterinary and Food Administration) and the National Food Institute, Technical University of Denmark were involved in the investigation. SSI is the national institute for surveillance and preparedness of human infectious diseases.
Infections were linked to a local shop which stopped production of food in mid-September this year. The specialty food store is called “Tyrkeren Odder” in Holsteinsgade, Odder, which is a town in Jutland, Denmark.
No new cases have been registered since August. Authorities advised consumers to throw out hummus, olives in oil, dates and other foods with high water activity purchased from the shop.
Six ill from 2016
The same type of Listeria monocytogenes was found in six people from 2016 to 2019. Five women and one man aged 30 to 91 years fell ill and at the time of illness, all patients lived in East Jutland. This led to officials suspecting infection came from food that was not sold in the rest of the country. Two people were sick in 2016, one in 2017 and three in 2019.
Whole genome sequencing of Listeria isolates allowed SSI to identify the outbreak and compare sequences from Listeria found in patients with those discovered in the food and production environment. Results showed they were similar and of sequence type 1.
In September 2019, interviews with the latest ill people found they had been shopping at the same store and eaten hummus made there. Information was also able to link one of those who fell ill in 2016 to the same location.
During a later inspection at the company, the Danish Veterinary and Food Administration found Listeria in a variety of hummus samples from the store and in the production area.
The store remains open to sell foods in retail packaging as well as fruits and vegetables but will have to meet criteria set by the authorities to resume food production.
Listeriosis symptoms may include sudden onset of fever, headache, backache, nausea, vomiting and neck stiffness. The time between becoming infected and developing symptoms varies from a few to 70 days with an average of three weeks. Infection is more serious for newborn babies, the elderly, immune suppressed people and pregnant women.
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