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Neighbour-joining phylogenetic analysis of the norovirus partial polymerase region B (172 bp) showing the relationship between noroviruses identified in samples from attendees at events 1–3 (▪), catering staff A, B and C (▲), environmental swab (♦) and selected reference noroviruses. Indistinguishable norovirus sequences are represented on the same node. Bootstrap values from 1000 replicates are shown where greater than 50%.
