In late 2012, a significant increase in norovirus associated outbreaks was identified in Ireland, a trend also noted in numerous countries across the northern hemisphere. Genogroup II genotype 4 (GII.4) has been the dominant strain of norovirus detected worldwide and in Ireland since 2002. However, norovirus evolves rapidly and since the mid 1990’s, new genetic variants of GII.4 have emerged and become the predominant strain on average every two to three years.
