Norovirus Illness Is a Global Problem: Emergence and Spread of Norovirus GII.4 Variants, 2001–2007

Background. Noroviruses (NoVs) are the most common cause of viral gastroenteritis. Their high incidence and importance in health care facilities result in a great impact on public health. Studies from around the world describing increasing prevalence have been difficult to compare because of differing nomenclatures for variants of the dominant genotype, GII.4. We studied the global patterns of GII.4 epidemiology in relation to its genetic diversity. Methods. Data from NoV outbreaks with dates of onset from January 2001 through March 2007 were collected from 15 institutions on 5 continents. Partial genome sequences (np775) were collected, allowing phylogenetic comparison of data from different countries. Results. The 15 institutions reported 3098 GII.4 outbreaks, 62% of all reported NoV outbreaks. Eight GII.4 variants were identified. Four had a global distribution—the 1996, 2002, 2004, and 2006b variants. The 2003Asia and 2006a variants caused epidemics, but they were geographically limited. Finally, the 2001Japan and 2001Henry variants were found across the world but at low frequencies. Conclusions. NoV epidemics resulted from the global spread of GII.4 strains that evolved under the influence of population immunity. Lineages show notable (and currently unexplained) differences in geographic prevalence. Establishing a global NoV network by which data on strains with the potential to cause pandemics can be rapidly exchanged may lead to improved prevention and intervention strategies.Financial support: European Commission, Directorate General Research Quality of Life program (EVENT [Enteric Virus Emergence, New Tools] grant SP22-CT-2004- 502571 to J.J.S.); Indian Council of Medical Research, New Delhi, India (support to S.B. and A.C.); New Zealand Ministry of Health (funding for the New Zealand studies); Hungarian Scientific Research Fund (grant F048433 to G.R.); 973 National Key Basic Research Program of China (grant 2007CB310500 to the Chinese Center for Disease Control and Prevention); Chilean National Science and Technology Research Fund (grants 10210583 and 1061079 to Y.L. and M.O.); Alberta Health and Wellness (support to B.E.L. and X.-L.P.); Ministry of Science, Technology, and Innovation, Malaysia (grant 06-02-05-001 BTK/ER/002 to N.B.G.R.)