Norovirus genotype diversity associated with gastroenteritis outbreaks in aged-care facilities

Noroviruses are a major cause of gastroenteritis. Vaccine strategies against norovirus are currently under consideration but depend on a detailed knowledge of the capsid genotypes. This study examined the incidence of norovirus outbreaks in residential aged-care facilities in Victoria, Australia over one year (2013) and documented the (capsid) norovirus genotypes associated with these outbreaks. It was found that 65·0% of 206 outbreaks tested were associated with norovirus infection, thereby showing norovirus to be the major cause of viral gastroenteritis in residential aged-care facilities. Fifteen capsid (open reading frame 2) genotypes were identified as follows: GI.2 (0·9%), GI.3 (1·8%), GI.4 (3·7%), GI.6 (0·9%), GI.7 (0·9%), GI.8 (0·9%), GII.1 (0·9%), GII.2 (0·9%), GII.3 (1·8%), GII.4 (2009-like) (0·9%), GII.4 (2012) (48·6%), GII.4 (2012-like) (16·5%), GII.4 (unknown) (9·2%), GII.5 (2·8%), GII.6 (0·9%), GII.7 (0·9%), GII.13 (6·4%) and an as yet unclassified GII genotype (0·9%). Although GII.4 was the most common norovirus capsid genotype detected, the great diversity of norovirus genotypes in the elderly indicates vaccination strategies for this demographic are not straightforward.