Effects and clinical significance of GII.4 Sydney norovirus, United States, 2012-2013

Emerg Infect Dis. 2013 Aug;19(8):1231-8. doi: 10.3201/eid1908.130458.


During 2012, global detection of a new norovirus (NoV) strain, GII.4 Sydney, raised concerns about its potential effect in the United States. We analyzed data from NoV outbreaks in 5 states and emergency department visits for gastrointestinal illness in 1 state during the 2012-13 season and compared the data with those of previous seasons. During August 2012-April 2013, a total of 637 NoV outbreaks were reported compared with 536 and 432 in 2011-2012 and 2010-2011 during the same period. The proportion of outbreaks attributed to GII.4 Sydney increased from 8% in September 2012 to 82% in March 2013. The increase in emergency department visits for gastrointestinal illness during the 2012-13 season was similar to that of previous seasons. GII.4 Sydney has become the predominant US NoV outbreak strain during the 2012-13 season, but its emergence did not cause outbreak activity to substantially increase from that of previous seasons.

Keywords: GII.4 Sydney strain; United States; enteric infections; norovirus; outbreak; surveillance; viruses.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Caliciviridae Infections / epidemiology*
  • Caliciviridae Infections / transmission
  • Caliciviridae Infections / virology
  • Disease Outbreaks*
  • Emergency Service, Hospital
  • Epidemiological Monitoring
  • Gastroenteritis / epidemiology*
  • Gastroenteritis / virology
  • Genotype
  • Hospitalization
  • Humans
  • Norovirus / genetics*
  • Phylogeny
  • Sequence Analysis, DNA
  • United States / epidemiology