Molecular epidemiology of norovirus strains circulating in Ireland from 2003 to 2004.

Since 2002, the burden of norovirus (NoV) infection in Ireland has increased. Outbreaks in institutional settings are the most common causing widespread disruption to health service delivery. This is the first national study of NoV in the Republic of Ireland and its aim was to identify the major NoV strains circulating in Ireland over a 13-month period between November 2003 and November 2004, inclusive. A prospective study screened faecal samples (n = 478) for NoV RNA. Positive samples (n = 116) were further analysed by a second PCR, targeted to the orf1/orf2 junction of the virus. Phylogenetic analysis was based on sequence alignments of this domain. GII/4 viruses represented 92.2% of sequences, 2.7% were GII/2, GII/3 and GGIIB cluster-like strains. The remaining 5.2% were of GI origin. NoV was detectable throughout the study period, although two peaks of infection were observed. The majority of infections were caused by a range of closely related GII/4 NoV strains.