Emergence of Norovirus GII.4 variants in acute gastroenteritis outbreaks in South Korea between 2006 and 2013.

BACKGROUND: New emerging strains of noroviruses (NoVs) often increase acute gastroenteritis (AGE) outbreaks worldwide. OBJECTIVE: We analyzed the epidemiological features and genotypic patterns of NoVs in AGE outbreaks. STUDY DESIGN: To elucidate the public health impact of NoVs during AGE outbreaks in South Korea, a molecular and epidemiological investigation was performed with 318 AGE outbreaks reported from the Gyeonggi province of South Korea during the period from 2006 to 2013. RESULTS: NoVs were associated with 102 (32.1%) of the AGE outbreaks. Epidemiological data revealed that the majority of NoV outbreaks were in the student group (47.1%), and the majority of AGE patients were identified in schools (68.8%). NoV genogroup (G) II strains were associated with 94 (92.2%) of the NoV outbreaks, and GII.4 strains were predominantly associated with 57.6% (n=49) of NoV GII outbreaks. Four GII.4 variants (2006b, 2007, 2009 and 2012 variants) emerged and showed different contributions to NoV outbreak activity. The 2006b variant was predominantly associated with NoV outbreaks during the early years of the study period, and was subsequently displaced by the New Orleans 2009 variant, and most recently by the Sydney 2012 variant. In addition, the GII.2, GII.14, and GII.17 strains have recently been often associated with NoV AGE outbreaks. CONCLUSIONS: The emergence of new NoV GII.4 variants significantly affected the NoV outbreak activity in South Korea during the period from 2006 to 2013. The surveillance for new emerging strains affecting NoV outbreak activity should be intensified to develop an adequate policy to prevent further NoV outbreaks.