Phylogenic analysis of norovirus sequences. The genetic relationship is based on a 322-nucleotides fragment of Region C (VP1). The tree was generated using the neighbor-joining method and the bootstrap values from 1000 replicates were shown on each branch. The sequence accession numbers are given in parentheses. The reference strains were from NCBI Genbank: Bristol(X76716), Fayetteville (AY113106), MinireovirusTV24 (U02030), CS-E1/2002/USA (AY502009), Tiffin-1999 (AY502010) and Variant Sydney 2012/FRA (KF008239).