Detection of the globally emerging GII.17[P17] norovirus during an acute gastroenteritis outbreak in Romania, 2024.

Norovirus is a major cause of acute gastroenteritis (AGE) globally. GII.17[P17] has been reported in the last decade as a prevalent norovirus genotype worldwide. We documented the circulation of norovirus GII.17[P17] isolates during an AGE outbreak occurring in western Romania, in 2024. Norovirus whole-genome sequences were obtained by Illumina technology and used for inferring phylogeny and to identify amino acid substitutions harboured by the VP1 major capsid protein and by the RNA-dependent RNA polymerase (RdRp). Phylogenetic analyses indicated high degree of relatedness between the Romanian isolates and the strains reported in Europe, United States, Argentina, and Japan between 2023 and 2025. All of these viruses belong to the Romania-2021 GII.17[P17] cluster, which also comprises isolates identified in Russia between 2021 and 2023. Substitutions in previously described VP1 epitope regions and in RdRp were detected. Continuous monitoring is needed to establish if the dominance of this cluster is local and transitory, as seen before for GII.17, or if it will become pandemic.