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Paradigm Shift Intervention Monitoring
Of the 36 flu viruses subtyped at the
state lab during week 51, 28 (78%) were seasonal A/H3N2, 3 (8%) were
unsutypeable (sic), 3 (8%) flu type B and 2 (6%) the 2009 A/H1N1.
The above comments from the week 51 report from Pennsylvania cite three unsubtypable samples, which is unusual in 2010. Last year there were samples that were influenza A positive but unsubtypable because they were swine H1N1, and subtyping was done with reagents directed against human H1 and human H3. The swine cases were subsequently identified with reagents that targeted the swine H1.
Pennsylvania has reported trH3N2 previously, but the trH3N2's have a human H3 from the mid-1990's. It is possible that the human H3 sub-typing reagents would fail to recognize trH3N2, because it continues to evolve away from seasonal H3.
If there really are three new trH3N2 cases in PA, it would be the highest number of novel influenza in a given state since pandemic H1N1 was identified in California (other than the subsequent pandemic H1N1 isolates identified after the California cases).
There have already been four trH3N2 cases identified in 2010 in the US, including the one in Pennsylvania, A/Pennsylvania/14/2010.
More information on the unsubtypable cases in Pennsylvania would be useful, and if these are three new trH3N2 cases, the sequences should be released and an alert should be made.