2008•Emerging infectious diseasesOpen access
Emergence of New Norovirus Variants on Spring Cruise Ships and Prediction of Winter Epidemics
Linda Verhoef, Evelyn Depoortere, Ingeborg L.A. Boxman, Erwin Duizer, Yvonne van Duynhoven, John Harris, Christina K. Johnsen, Annelies Kroneman, Soizick Le Guyader, Wilina Lim, Leena Maunula, H Meldal, Rod Ratcliff, Gábor Reuter, E. Schreier, J. Joukje Siebenga, Kirsti Vainio, Carmen Varela, Harry Vennema, Marion Koopmans, on behalf of the Food Borne Viruses in Europe Network
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Abstract
In June 2006, reported outbreaks of norovirus on cruise ships suddenly increased; 43 outbreaks occurred on 13 vessels.All outbreaks investigated manifested person-toperson transmission.Detection of a point source was impossible because of limited investigation of initial outbreaks and data sharing.The most probable explanation for these outbreaks is increased norovirus activity in the community, which coincided with the emergence of 2 new GGII.4variant strains in Europe and the Pacifi c.As in 2002, a new GGII.4variant detected in the spring and summer corresponded with high norovirus activity in the subsequent winter.Because outbreaks on cruise ships are likely to occur when new variants circulate, an active reporting system could function as an early warning system.Internationally accepted guidelines are needed for reporting, investigating, and controlling norovirus illness on cruise ships in Europe.N orovirus is a highly infectious causal agent of a usu- ally mild and self-limiting acute gastroenteritis.The symptoms of vomiting and diarrhea occur after a short incubation period of 8 to 72 hours.Although norovirus can cause sporadic cases (1), this contagious virus is often de-scribed as a cause of outbreaks (2-5).In Europe, norovirus outbreaks are reported to the Food Borne Viruses in Europe (FBVE) network.This network maintains a Webbased surveillance database containing data reported by 13 European countries (6).In June 2006, the Dutch Food and Consumer Product Safety Authority (VWA) contacted the coordinator of the FBVE network, located at the National Institute for Public Health and the Environment (RIVM) in the Netherlands.The VWA had been notifi ed of suspected norovirus outbreaks on 3 cruise ships operating in the Netherlands in the previous month.In the same week, ProMED reported a viral gastroenteritis outbreak on a Dutch-owned cruise ship operating out of the United Kingdom (7).Norovirus outbreaks on cruise ships are not normally reported to national surveillance centers in Europe, but having been alerted to Emergence of New Norovirus Variants on Spring Cruise Ships and Prediction of Winter Epidemics
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