Molecular epidemiology analysis of symptomatic and asymptomatic norovirus infections in Chinese infants

Background: Norovirus, is the leading cause of acute gastroenteritis among children. Previous studies based on symptomatic infections indicated that mutations, rather than recombination drove the evolution of the ORF2 for norovirus. However, strains causing asymptomatic infection were not considered. Methods: we conduct the first norovirus molecular epidemiology analysis covering both symptomatic and asymptomatic infections derived from a birth cohort study in the northern China. Results: During the study, 14 symptomatic and 20 asymptomatic norovirus infections were detected in 32 infants. Out of the 14 strains that caused symptomatic infections, 12 strains were identified as GII.3 [P12], and others were GII.4 [P31]; conversely, 17 asymptomatic infections were caused by GII.4 [P31], two by GII.2 [P16], and one by GII.4 [P16]. Regardless whether symptomatic and asymptomatic the mutations were detected frequently in the ORF2 region, and almost all recombinations were identified in the RdRp region. The majority of the mutations were located around the predefined epitope regions of P2 subdomain indicating a potential for immune evasion. Conclusion: The role of asymptomatic infection in the evolution of noroviruses needs to be evaluated continuously.