Molecular epidemiology of norovirus GII.4 variants in children under 5 years with sporadic acute gastroenteritis in South Korea during 2006-2013

Background: The global emergence of norovirus (NoV) GII.4 variants has raised public concerns in the world including South Korea since 1996. Objective: We analyzed seasonality and genotypic pattern for sporadic cases by norovirus GII-4 variants. Study design: To determine the epidemic status of GII.4 variants in South Korea during 2006-2013, 7301 fecal specimens were collected from children who were younger than 5 years and had sporadic acute gastroenteritis (AGE). Results: During the study period, NoVs were the most prevalent viral agent, detected in 877 (12.0%) of the 7301 fecal specimens from children with sporadic AGE. NoV GII strains predominantly accounted for 97.6% of all sporadic NoV infections. NoV GII.4 was the most prevalent genotype and comprised 67.6% of the NoV GII strains. However, seasonal prevalence of GII.4 strains varied depending on the spread of GII.4 variants. GII.4-2006b variant most predominantly circulated from 2006-2007 to 2009-2010 and persisted during other seasons. GII.4-2009 variant was first detected in January 2010 and predominant in 2011-2012. However, it was rapidly displaced by GII.4-2012 variant, which emerged in May 2012 and substantially circulated in 2012-2013. Conclusions: The frequent emergence and rapid spread of GII.4 variants significantly affect the magnitude of sporadic NoV infections in children. Hence, to minimize the disease burden of NoV infections, GII.4 strains should be considered as a primary target for vaccine development against NoVs.