Danish illnesses traced to lettuce from France
Statens Serum Institut, DTU Fødevareinstituttet and Fødevarestyrelsen (SSI, the Technical University of Denmark and the Danish Veterinary and Food Administration) investigated several outbreaks which started in April.
A total of 23 outbreaks were investigated, including 1,497 people from various companies. Among these 412 (28%) fell ill with vomiting and/or diarrhoea.
Salad was sold primarily for restaurants and caterers and because it was used in professional kitchens, the infection spread to several companies and guests in a short time, said DVFA.
The cause of contamination of the lettuce remains unknown.
Lollo Bionda lettuce link
Epidemiological cohort studies in two of the affected companies pointed towards dishes that included Lollo Bionda lettuce. This was underpinned by investigations from other companies that had received the same lettuce, said SSI.
Tracking of the lettuce demonstrated that the product in question was a Lollo Bionda lettuce of French origin marketed by one company.
The product was primarily sold to restaurants and catering companies through a wholesale merchant. A.P. Grønt (A. P. Vegetables) based in Slangerup withdrew the salad in early April.
Norovirus infection was confirmed on the basis of 28 patient samples in which genogroup I (GI) was found.
Additional typing of the virus from 22 patients from nine different companies demonstrated that all had the same subtype of norovirus (genotype GI.P2-GI.2), which supported the hypothesis of a common foodborne source of infection.
DTU finds match
DTU Food tested lettuce from several outbreaks, and in one head of lettuce the Institute found a low number of norovirus particles of the same genogroup found in the patients.
Researchers said it is the first time that a norovirus outbreak in Denmark had provided such large number of human samples from various sub-clusters during the investigation.
“The outbreak demonstrates that contaminated lettuce sold to catering companies holds a considerable potential for infection of a large number of persons within a very limited time span which, in turn, underlines the importance of rapid investigation, timely sampling of patients and foods, and of willingness to withdraw products on the part of the foodstuffs companies based only on a suspicion with respect to the source of infection,” said SSI.
It is the second time that Lollo Bionda lettuce from France has caused a series of outbreaks - the first was in 2010. More than 250 people were sickened in 10 different outbreaks six years ago.
A cohort investigation performed in a company where several types of food had been served pointed to sandwiches containing lettuce as the cause of disease.
Norovirus is highly contagious and it is possible to get sick by eating food contaminated with only a few virus particles.
