Commentary
Canada
Advises Against
Tamiflu Treatment of Seasonal Flu?
Recombinomics Commentary
15:53
December 29, 2008
assessed genotypically for oseltamivir resistance; 14 showed this resistance mutation, and the other 5 were indeterminate.
The above comments from the British Columbia Influenza Surveillance Update for weeks 49-50 indicate that the seasonal flu situation in Canada is similar to the United States, where most of the influenza is influenza A, and most of the influenza A is H1N1.
Earlier reports from the Canadian Flu Watch suggested similar data, but those isolates were not sub-typed, so it was hard to determine the ration of H1 to H3. The first isolated tested was H1N1 and Tamiflu resistant (H274Y), but that result was known at the beginning of the season, and was not updated until last week, when the number of H1N1 isolates tested rose to three and all three had H274Y. However, the limited amount of testing did not adress the H1/H3 ratio.
The above comments on isolates in British Columbia indicate that like the United States, most influenza A is H1N1. In the US only one H1N1 isolate has been sensitive to oseltamivir, and that isolate was clade IIC (Hong Kong/2652), which is oseltamivir sensitive, but amantadine sensitive. Thus, in the US clade IIC has been rare, which is also true for Europe, where there has also only one reported Tamiflu sensitive isolate, and it is also likely to be clade IIC.
Last season about 10% of H1N1 in the US was IIC and all were amantadine sensitive (S31N in M2). Thus, this season the amantadine resistance in IIC remains at 100%, but clade IIB (Brisbane/59) dominates. The above report of H274Y in all interpretable tests also suggests that H274Y is at 100% in clade IIB in Canada and clade IIC is rare this season in Canada.
Thus, Canada, like the United States should issue an alert on treating influenza with Tamiflu, since most of the flu in Canada also ahs H274Y.
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