Proposal for a unified norovirus nomenclature and genotyping Annelies KronemanEverardo VegaHarry VennemaJan Vinje ´ • Peter A. WhiteGrant HansmanKim GreenVito MartellaKazuhiko Katayama •

Noroviruses belong to a genus of genetically diverse viruses within the family Caliciviridae and cause acute gastroenteritis in humans and animals. They are subdivided into genogroups, each of which further segre- gates into genotypes. Until recently, a new genotype was based on a defined pairwise distance cutoff of complete VP1 sequences, but with the increasing number of avail- able norovirus sequences, this cutoff is no longer accurate, and sequences in the public database have been misclas- sified. In this paper, we demonstrate that the pairwise distance cutoff method can no longer be used and outline a phylogenetic approach to classify noroviruses. Further- more, we propose a dual nomenclature using both ORF1 and VP1 sequences, as recombination is common and recognizing recombinant viruses may be relevant. With the continuing emergence of new norovirus lineages, we pro- pose to coordinate nomenclature of new norovirus geno- types through an international norovirus working group.