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Maine trH3N2 Inconclusive Sub-typing Raises Concerns
Recombinomics Commentary 20:30
October 20, 2011

HETL detected a case of influenza A virus that was inconclusive during subtyping. On October 17 Federal CDC confirmed this isolate to be the 5th recognized case of human infection with S-OtrH3N2 with the M segment gene from the pH1N1virus (also identified in one case in Indiana and three cases in Pennsylvania). Investigation is ongoing. More information can be found in a Health Alert, released 10/19/2011

The above comments are from the Maine CDC week 41 report and confirm testing issues with trH3N2 cases, including the Maine case (8M), A/Maine/06/2011.  As noted the Maine H3 sequence is closer to the dominant human trH3N2 isolates from 2010 (as seen in sequences from A/Pennsylvania/40/2010, A/Wisconsin/12/2010, A/Minnesota/11/2010, and presumably the daughter of A/Minnesota/11/2010), which likely produce an “inconclusive” result.  The 2010 H3 sequence was recognized by seasonal H3 reagents, leading to a 5 month delay in reporting the case as novel trH3N2.  In contrast, the 2011 sequences from Indiana and Pennsylvania had evolved away from the 2010 sequences, leading to an “unsubtypable” designation.  The Maine H3 was closer to the 2010 sequence leading to an “inconclusive result. 

Thus, current trH3n2 cases may given a spectrum of results fluctuating between seasonal H3 and pandemic H3, leading to a gross under-representation of true trH3N2 levels and bizarre postings in FluView.

There has been no direct evidence linking any of the trH3N2 cases to swine.  The Indiana case had no swine contact, and the Pennsylvania and Maine cases attended agricultural fairs, and that linkage led to more testing, but provided no real evidence that the trH3N2 came from swine at the fairs.  In the maine case, a lack of a link may have avoided the doctor’s visit, or may have prevented shipment of the sample to the state lab, or may have ended testing when an inconclusive result was obtained.  Thus, the vast majority of trH3N2 cases would not be tested by the CDC in Atlanta, the only lab routinely testing for trH3N2.

The inconclusive result for the Maine case highlights the need from PCR H3 testing kits at state labs, which should be distributed immediately to determine the true extent of trH3N2 infections in the United States.

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