Indications for worldwide increased norovirus activity associated with emergence of a new variant of genotype II.4, late 2012 van Beek, J and Ambert-Balay, K and Botteldoorn, N and Eden, J S and Fonager, J and Hewitt, J and Iritani, N and Kroneman, A and Vennema, H and Vinjé, J and White, P A and Koopmans, M and on behalf of NoroNet, Collective, Eurosurveillance, 18, 20345 (2013), https://doi.org/10.2807/ese.18.01.20345-en