Noroviruses in children seen in a hospital for acute gastroenteritis in Finland

Noroviruses (NoVs) are second only to rotaviruses (RVs) as causative agents of acute gastroenteritis (AGE) in children. The proportional role of NoVs is likely to increase after control of RV by vaccination. We investigated NoVs in children seen in Tampere University Hospital either treated as outpatients or hospitalized because of AGE before universal RV vaccination was implemented in Finland. This prospective study was conducted from September 2006 to August 2008. A total of 1,128 children <15 years of age with symptoms of AGE were enrolled either in the hospital clinic or in a ward, and stool samples for NoV studies were obtained from 759 children. NoVs were found in 196 (26%) cases. In the first year, NoVs were found in 116 (34%) out of 341, and in the second year, in 80 (19%) out of 418 cases. RVs were found respectively in 128 (38%) and 260 (62%) cases in these two seasons. Both RV and NoV were present in 24 cases. NoV genotype GII.4 predominated with a 96% share of the NoV cases in the first season and an 80% share in the second season. Other NoV genotypes seen infrequently were GII.7, GIIb, GI.6, GII.1, GII.2, and GIIc. The median clinical severity of NoV AGE was 14 compared to 16 for RV AGE on a 20-point scale. Conclusion: NoVs were nearly as common as RVs as causative agents of severe AGE in children seen in hospital. After implementing universal RV vaccination, the importance of NoVs will still increase further.