The molecular epidemiology of norovirus outbreaks in Victoria, 2014 to 2015 .

Noroviruses are a leading cause of outbreaks of gastroenteritis. This study examined the incidence and molecular characteristics of norovirus outbreaks in healthcare and non-healthcare settings in Victoria, Australia, over 2 years (2014-2015). Norovirus was detected in 65.7% and 60.4% of gastroenteritis outbreaks investigated for the years 2014 and 2015 respectively. There was a significant decline in the number of norovirus outbreaks in the period 2014 to 2015 although in both years norovirus outbreaks peaked in the latter part of the year. Norovirus Open Reading Frame (ORF) 2 (capsid) genotypes identified included GI.2, GI.3, GI.4, GI.5, GI.6, GI.9, GII.2, GII.3, GII.4, GII.6, GII.7, GII.8, GII.13 and GII.17. GII.4 was the most common genotype detected. In addition, the following ORF 1/ORF 2 recombinant forms were confirmed: GII.P4_NewOrleans_2009/GII.4_Sydney_2012, GII.P12/GII.3, GII.Pb (GII.21)/GII.3, GII.Pe/GII.2 and GII.Pe/GII.4_Sydney_2012. A significant decline was noted in the chief norovirus strain GII.Pe/GII.4_Sydney_2012 between 2014 and 2015 but there was a re-emergence of a GII.P4_ NewOrleans _2009 norovirus strain. Outbreaks involving the GII.P17/GII.17 genotype were also detected for the first time in Victoria. GI genotypes circulating in Victoria for the 2 years 2014 and 2015 underwent a dramatic change between the 2 years of the survey. Many genotypes could occur in both healthcare and non-healthcare settings although GI.3, GII.6, and GII.4 were significantly more common in healthcare settings. The study emphasises the complex way in which norovirus circulates throughout the community.