Y-026. Epidemics of Gastroenteritis by Norovirus GII.4 Variants in Australia and New Zealand, 2006-2007

E. T. Tu1,2, R. A. Bull1,2, G. E. Greening3, J. Hewitt3, M. J. Lyon4, J. A. Marshall5, J-S. Eden1, D. Smith6, C. J. McIver1,2, W. D. Rawlinson1,2, P. A. White1;
1Univ. of New South Wales, Sydney, AUSTRALIA, 2Prince of Wales Hosp., Sydney, AUSTRALIA, 3Inst. of Environmental Sci. and Res. Ltd., Porirua, NEW ZEALAND, 4Queensland Hlth. Sci. Services, Brisbane, AUSTRALIA, 5Victorian Infectious Diseases Reference Lab., Victoria, AUSTRALIA, 6QEII Med. Ctr., Perth, AUSTRALIA.

Background: Acute gastroenteritis is commonly associated with norovirus (NoV) genogroup II (GII) infection. NoV GII has 17 classified genotypes (GII.1-GII.17), but only one, NoV genotype GII.4, is associated with at least four global epidemics of gastroenteritis. During early 2006, a marked increase in outbreaks of gastroenteritis occurred in Australia, New Zealand, Asia, Europe, USA and Canada. This increase in NoV activity was similar to the trend recorded in those countries during 2004. Methods: Between December 2005 and August 2007, 305 faecal samples were collected from patients with acute gastroenteritis from around Australia and New Zealand. Nested reverse transcription-polymerase chain reaction, sequencing and phylogenetic analysis of a 266 base-pair fragment of the capsid gene from 249 specimens was used to determine NoV genotype. Further phylogenetic analysis was performed to determine if the virus was a recombinant or related to previous pandemic strains: US95/96 virus (1996), Farmington Hills virus (2002) and Hunter virus (2004). Results: The increase in NoV gastroenteritis in 2006 was associated with the emergence of two new GII.4 variants, 2006a and 2006b. 2006a was the dominant strain between February to August 2006 and was identified in 60% of the 193 cases investigated in 2006. After July 2006, 2006b was the predominant strain, causing 8 of 14 (57%) outbreaks investigated between August to December 2006. However, in 2007, 2006b was the sole aetiological agent identified in over 26 outbreaks and had completely replaced 2006a. NoV 2006a and 2006b have also been implicated as the predominant causes of NoV associated gastroenteritis across Europe, North America and Asia in 2006. A number of recombinant viruses were identified as the aetiological agents in 19 of 249 (8%) cases of gastroenteritis. Conclusion: The increase in NoV associated gastroenteritis in 2006 and 2007 was linked to the emergence and co-circulation of two novel GII.4 variants, 2006a and 2006b.