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. Objectives: To compare proportions of amantadine-resistant influenza A (H1N1) and (H3N2) isolates in the Greater Toronto Area. Study design: 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 (H I NI) 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. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved.