Differential patterns of amantadine-resistance in influenza A (H3N2) and (H1N1) isolates in Toronto, Canada.
BACKGROUND
Molecular methods were used to characterize influenza A (H1N1) and (H3N2) strains and to identify amantadine-resistance.


OBJECTIVE
To compare proportions of amantadine-resistant influenza A (H1N1) and (H3N2) isolates in the Greater Toronto Area.


METHODS
Isolates of influenza A (H1N1) and (H3N2) were strain typed using molecular methods. Pyrosequencing for point mutations in the transmembrane domain of the M2 proton channel was undertaken. Proportions of amantadine-resistant and susceptible isolates were compared using the The Fisher's exact test.


RESULTS
96% of the 49 influenza A (H3N2) isolates and none of the influenza A (H1N1) tested carried a point mutation in the M gene coding for the M2 protein. Influenza A (H3N2) isolates were more likely to carry an amantadine-resistance associated mutation than influenza A (H1N1) isolates (Fishers's exact test, P<0.0001).


CONCLUSIONS
: Characterization of amantadine-resistance in influenza A (H1N1) isolates should utilize a variety of different methods including sub-typing, strain typing, and direct sequencing for point mutations associated with amantadine-resistance.
Higgins
Rachel R
RR
Central Public Health Laboratory, Toronto, ON, Canada.
Eshaghi
A
A
Burton
L
L
Mazzulli
T
T
Drews
S J
SJ
D000547:Amantadine / Q000494:pharmacology*; D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology*; D002170:Canada; D024882:Drug Resistance, Viral; D005838:Genotype; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects* / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects* / Q000302:isolation & purification; D007251:Influenza, Human / Q000821:virology*; D020125:Mutation, Missense; D017354:Point Mutation; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA; D014763:Viral Matrix Proteins / Q000235:genetics; D000086082:Viroporin Proteins
D000547:Amantadine; D000998:Antiviral Agents; D012367:RNA, Viral; D014763:Viral Matrix Proteins; C488937:M2 protein, Influenza A virus; D000086082:Viroporin Proteins