Norovirus genotype diversity associated with gastroenteritis outbreaks in Victoria in 2013.

The noroviruses are now considered a leading cause of outbreaks of non-bacterial gastroenteritis worldwide. 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 Victoria over 1 year (2013) and documented the genotypes occurring in the different outbreak settings (healthcare and non-healthcare) and age groups. It was found that 63.1% of gastroenteritis outbreaks were associated with norovirus, thereby showing norovirus to be the major viral cause of illness in gastroenteritis outbreaks. Sixteen capsid genotypes were identified and included GI.2, GI.3, GI.4, GI.6, GI.7, GI.8, GI.9, GII.1, GII.2, GII.3, GII.4, GII.5, GII.6, GII.7, GII.13 and an as yet unclassified GII genotype. All genotypes found in the study, with the exception of GI.9, were detected in the elderly, indicating prior exposure to a norovirus genotype did not appear to confer long term immunity in many cases. The incidence of genotypes GII.1, GII.4 and GII.7 was linked with setting and age. As setting and age were correlated it was not possible to determine which variable was critical with the exception of GII.7, which appeared to be linked to age. The findings indicate that norovirus vaccine strategies should encompass a broad range of genotypes and, as setting or age may be important in determining genotype incidence, this should be taken into account as well.