High frequency of amantadine-resistant influenza A (H3N2) viruses in the 2005-2006 season and rapid detection of amantadine-resistant influenza A (H3N2) viruses by MAMA-PCR.

Using the newly designed mismatch amplification mutation assay (MAMA) PCR, we demonstrated the high frequency of amantadine-resistant influenza A (H3N2) viruses isolated during the 2005-2006 season by detecting the mutation at amino acid position 31 of the M2 protein (S31N). Further, phylogenetic analyses of the HA1 sequences of the S31N viruses revealed that they comprised a clonal lineage that would result in the common characteristic amino acid changes at positions 193 (Ser to Phe) and 225 (Asp to Asn) of the HA protein. We also demonstrated that the S31N/S193F/D225N viruses had already emerged in Aichi Prefecture by the end of the previous 2004-2005 season.