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Paradigm Shift Intervention Monitoring
Myth On H3N2v Matches In Ohio Swine
The above comment by CIDRAP is confusing at best. Most would read the phrase “they have been finding only the novel H3N2 strain that contains the matrix gene from the 2009 H1N1 virus” as a match with H3N2v in 2012 human cases since the above phrase is followed by the claim that the “same strain, called H3N2v, has infected nearly 170 people….” However, that interpretation would be false.
The CDC has released an update from the USDA, which has found swine isolates, including four June, 2012 isolates in Ohio, which have the H1N1pdm09 M gene (which are now being called H3N2pM by the CDC), which cites 57 H3N2pM isolates during FY2012 (collected after October 1, 2011). Sequences from 45 of these 57 isolates are public (at Genbank), and only 19 of the 45 H3N2pM sequences have an HA and NA that match the human H3N2v cases from 2011 and 2012. However, only 2 of the 19 sequences have an NA that matches the 2012 human H3N2v sequences, which are distinct from the first 10 human isolates from 2011.
Thus, the four June, 2012 swine isolates from Ohio have a match with the 2011 sub-clade which has not been reported in any of the 18 case from 2012, which includes 7 cases from Ohio and 9 cases from Indiana. The vast majority of the 170 cases cited in the CIDRAP quote are from Ohio or Indiana.
The failure of CIDRAP and the CDC to note the clear difference between the H3N2v sub-clade found in the first 10 cases in 2011 and the 18 cases in 2012, which match the cases from West Virginia, creates the media myth that the linkage between the H3N2v cases and agricultural fairs is due to swine to human transmission instead of extreme CDC sample bias (which largely limits testing to ILI cases with swine exposure).
The recent announcement by the CDC of expanded testing of ILI without swine exposure is long overdue, but efforts to correct misstatements by the CDC and CIDRAP would improve attempts to restore balance in off season testing of ILI cases, which has created a widely cited media myth on H3N2v jumping from pigs to people.