Characterization of norovirus strains in Australian children from 2006 to 2008: prevalence of recombinant strains.

Noroviruses are highly infectious and are the most common cause of gastroenteritis outbreaks. Genotype II.4 strains have been the dominant type identified in adults, however the genotype distribution in children is less clearly defined. This study aimed to detect and genotype norovirus strains infecting children hospitalized with acute gastroenteritis in Melbourne, Australia from 2006 to 2008. Stool samples were collected from 272 children admitted to the Royal Children's Hospital, Melbourne, Australia, with non-rotavirus acute gastroenteritis between April 2006 and December 2008. Using RT-PCR, norovirus was detected in 36% of samples. Strains were genetically characterized via analysis of regions from both the capsid gene and the RNA dependent RNA polymerase (RdRp) gene, to investigate genotype distribution and incidence of recombination. Typing based on the capsid gene (n = 70) detected GII.4 (49%) and GII.3 (46%) as the most predominant genotypes. Strains with a GII.4 capsid were usually assigned a GII.4 RdRp, whereas most strains identified as GII.3 based on capsid typing were assigned a GIIb RdRp (71%). The GII.3/GIIb represent recombinant strains. Sequence analysis of the putative recombination breakpoint was performed for three representative suspected recombinants: GII.3/GIIb (n = 2) and GII.3/GII.12 (n = 1). Recombination analysis confirmed these strains as recombinants and identified putative breakpoints adjacent to the ORF1/ORF2 junction. This study highlights the importance of norovirus infection as a cause of pediatric gastroenteritis. It also reinforces the high circulation of recombinant strains causing disease in children, particularly the GII.3/GIIb strain.