Separate norovirus outbreaks linked to one source of imported frozen raspberries by molecular analysis, Denmark, 2010-2011.

Norovirus outbreaks occur frequently in Denmark and it can be difficult to establish whether apparently independent outbreaks have the same origin. Here we report on six outbreaks linked to frozen raspberries, investigated separately over a period of 3 months. Norovirus from stools were sequence-typed; including extended sequencing of 1138 bp encompassing the hypervariable P2 region of the capsid gene. Norovirus was detected in 27 stool samples. Genotyping showed genotype GI.Pb_GI.6 (polymerase/capsid) with 100% identical sequences. Samples from five outbreaks were furthermore identical over the variable capsid P2 region. In one outbreak at a hospital canteen, frozen raspberries was associated with illness by cohort investigation (relative risk 6·1, 95% confidence interval 3·2-11). Bags of raspberries suspected to be the source were positive for genogroup I and II noroviruses, one typable virus was genotype GI.6 (capsid). These molecular investigations showed that the apparently independent outbreaks were the result of one contamination event of frozen raspberries. The contaminated raspberries originated from a single producer in Serbia and were originally not considered to belong to the same batch. The outbreaks led to consultations and mutual visits between producers, investigators and authorities. Further, Danish legislation was changed to make heat-treatment of frozen raspberries compulsory in professional catering establishments.

Endemic hepatitis E in two Nordic countries.

Antibodies against hepatitis E virus (anti-HEV) were found in 248 Swedish and Danish patients between 1993 and 2007. Most patients were symptomatic and tested for anti-HEV due to travel abroad. Among patients with known country of infection, most were infected in Asia, mainly on the Indian subcontinent. However, 29 patients were infected in Europe, nine of these had HEV IgM and/or HEV RNA in serum. In sera from 65 of 141 tested patients HEV RNA could be detected, and 63 strains could be typed by limited sequencing within ORF2. HEV RNA was found in sera from 71% of the patients with HEV IgM and IgG and in 18% of the patients with only detectable HEV IgG. It was also found up to three weeks after the onset of disease in 67% of the patients with known date of onset. Patients infected in Europe were infected by genotype 3, and were older than those infected by genotype 1 (mean age 55.3 vs 30 years, p<0.001). Since it is known that genotype 3 can infect domestic pigs, HEV strains from 18 piglets in 17 herds in Sweden and Denmark were sequenced. Phylogenetic analyses of the genotype 3 strains showed geographical clades and high similarity between strains from patients and pigs from the same area. There are thus autochthonous hepatitis E cases in Scandinavia, and there are probably many undiagnosed ones. Patients with hepatitis of unknown etiology should therefore be investigated for anti-HEV even if they have not been outside Europe, since infections acquired from pigs or other animals should be taken into consideration.