Molecular and epidemiological features of GIIb norovirus outbreaks in Victoria, Australia, 2002–2005

The epidemiology of GIIb norovirus outbreaks and the characteristics of GIIb open reading frame (ORF) 2 recombinant forms are poorly understood and this study examined these questions using norovirus-associated gastroenteritis outbreaks in Victoria, Australia, during 2002-2005. Twenty-one GIIb outbreaks were detected and were the second most common ORF 1 norovirus outbreak genotype (5%) after GII.4 (90%). Both GIIb and GII.4 outbreaks peaked in warmer months of the year but their periodicity was different. ORF 2 sequencing analysis was carried out in the two regions previously designated C and D. RT-PCR region D primers were less sensitive than region C primers. No evidence of recombination between regions C and D was found. ORF 2 genotypes for the 21 GIIb outbreaks were: GII.1 (10 outbreaks), GII.3 (10 outbreaks) and, apparently for the first time, GII.13 (1 outbreak). GIIb outbreaks could occur in a broad range of settings and there was no correlation between ORF 2 genotype and setting except that all 5 outbreaks involving mainly young children were associated with GIIb/GII.3.