Abstract

Institutes charged with the surveillance of norovirus (NoV) outbreaks in Ireland, Germany, the Netherlands and Sweden reported high NoV activity to the European Food-borne Viruses in Europe network (FBVE) in late 2007. In these countries, the number of reported NoV outbreaks exceeds that of October and November of the previous record seasons, 2004 and 2006. A similar situation has been reported in the United Kingdom (UK) [1]. In recent years, most norovirus outbreaks have been caused by GII.4 strains. These viruses evolve rapidly by genetic mutation coupled with selective pressure. The rapid evolution of GII.4 noroviruses resulting in the successive emergence of new variants has been observed since 2002. In the norovirus outbreak season of 2006-7, two variants emerged that co-circulated. Early observations for the 2007-8 season suggest that one of these variants now dominates. The currently circulating strains have mutations that set them apart from the older strains, leading to one amino acid change in the capsid sequence. Although we do not consider the strains that currently circulate as new variants, based on the global character of norovirus and previous experience with high numbers of reported outbreaks we are expecting high norovirus activity in other countries. .