Series of Norovirus Outbreaks Caused by Consumption of Green Coral Lettuce, Denmark, April 2016

• Published in: PLoS currents Vol. 8
• Main Authors: Müller, Luise, Rasmussen, Lasse Dam, Jensen, Tenna, Schultz, Anna Charlotte, Kjelsø, Charlotte, Barnadas, Celine, Sigsgaard, Kim, Larsen, Anne Ribert, Widstrup Jensen, Carl, Jeppesen, Simon, Uhrbrand, Katrine, Hove, Nikolas, Mølbak, Kåre, Ethelberg, Steen
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 04.10.2016
• ISSN: 2157-3999; 2157-3999
• DOI: 10.1371/currents.outbreaks.115761d5d6de6a8bc7dd4b41f0f5f142

In early April 2016, an unusual high number of point-source outbreaks of gastrointestinal disease were reported to occur in Denmark. Outbreaks were individually investigated. Two analytical studies were performed. Patient stool samples collected and analysed; positive stool samples were sequenced over the polymerase and/or capsid gene areas. Implicated lettuce heads were collected and analysed for the presence of norovirus. Foods were traced-back and traced-forward and international alert systems applied. A total of 23 linked point-source outbreaks occurred over the course of one week. Fresh green coral lettuce (Lollo Bionda lettuce) had been consumed in all settings. In a cohort study including 234 participants a dish containing green lettuce was associated with illness. Norovirus of Genogroup I (GI) was detected in samples from 28 patients comprising eight of the outbreaks. Sequencing showed GI.P2-GI.2. GI norovirus was detected in one of 20 examined lettuce heads. All lettuce consumed was supplied by the same packer who in turn had bought the lettuce from a wholesaler in France. The two lots of lettuce came from two different growers in different parts of France. Green coral lettuce produced in France was found to have caused a large series of linked norovirus outbreaks in Denmark as established by a number of lines of evidence. A similar incidence occurred in 2010. Fresh lettuce increasingly appear to be a risk food for norovirus infections.