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Paradigm Shift Intervention Monitoring
Match Raises Concerns
Animal and public health investigations are currently underway to determine the source of this infection and if there are additional human cases.
Although the CDC has not yet released sequences from the first confirmed H3N2v case in 2012, the above description strongly suggests that the lineage of the Utah case will match the first 10 cases in 2011 or the two most recent cases (from West Virginia).
This similarity strongly suggests that the H3N2v is transmitting human to human, even though the current case had exposure to swine at a family slaughterhouse one week prior to disease onset. The extent of exposure is unclear, and H3N2v in Utah swine has not been reported. To date there have only been two examples (NY and IA) of swine matches of the H3N2 identified in the first 10 cases in 2011, and the five most recent cases in 2011 had no swine exposure.
Moreover, the five cases formed two clusters. In addition to the three confirmed cases in Iowa, the brother and father of the index case were symptomatic but not tested. H3N2v was confirmed in two classmates of the index case, and all three sets of sequences were virtually identical. Similarly, the cluster in West Virginia had a constellation of flu genes which were similar to the 10 prior cases, but had an N2 from a different lineage. Moreover, 22 additional contacts were symptomatic, but not tested.
The evolution of the H3N2v also supports human to human transmission. In 2010 most of the flu genes from most of the human cases were of the same lineage, and two of the isolates matched in all 8 gene segments. The matching isolates were the parental sequences for 5 of the 8 gene in the 2011 isolates. The other three gene segments including an H1N1pdm09 M gene were from an H1N2 parent swine sequence from Ohio (A/swine/Ohio/FAH10-1/2010). This combination was found in all of the first ten cases, even though they were isolates from four states (Indiana, Pennsylvania, Maine, Iowa). The final two match in 7 of the 8 genes (the N2 was from swine H3N2).
The CDC description strongly suggests that the lineages that were dominant in 2011 are once again present in 2012, strongly supporting human to human transmission. Release of the sequences from the Utah case would be useful.