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CDC Have You
Heard? Exposure On 2nd Maine trH3N2 Case
Both of the most recent patients confirmed with swine–origin influenza A (H3N2) infection had been in close contact with live pigs during the week prior to their illness onset.
The above comments are from the CDC’s November 4, 2011 “Have You Heard?” entitled “CDC Confirms the 6th and 7th Cases of Swine-Origin Influenza A H3N2 Virus with 2009 H1N1 M Gene” and is the fifth installment on its series on H3N2 triple reassortants (trH3N2). Have You Heard? publications are designed to give media background on significant news stories from the CDC, and many media reports heavily rely on these “Have You Heard?” publications at the CDC website targeting media. The “Have You Heard?” link is on the CDC media page, and the series is on the CDC Online Newsroom page. The above comments are on the two most recent trH3N2 cases, which were described in the week 43 FluView, which stated “Both patients reported close contacts with pigs preceding their illness onset” and gave no timing for the contact relative to the development of symptoms, which is a key metric for evaluation “swine exposure” since the incubation time for influenza is short (2 days with a range of 1-4 days), and the absence of a time frame in the week 43 FluView is a major issue.
The above “Have You Heard?” claims “close contact with pigs during the week prior to their illness onset”, but the “confirmation” in the first sentence links to the week 41 FluView, which described the first Maine case, A/Maine/06/2011, and not the second case, A/Maine/07/2011, suggesting the cited exposure date is incorrect.
The claim of contact with live pigs in the week prior to disease onset is at odds with comments by the Maine CDC and Department of Agriculture, which were contacted by Recombinomics. Both cases were said to have had contact at a state agricultural fair, and one of the cases participated in a "pig scramble". Comments on tests of swine from “the fair” suggested both cases had exposure at the same fair, which was almost certainly the Cumberland Fair which was open from September 25 – October 1, and the pig scramble was at 9 AM on October 1. A video of the scramble was posted on youtube. The swine on the video appeared to be healthy and quicker than the 10 boys, leading to minimal contact between the pigs and the 10 boys selected to participate, which was limited to residents of Cumberland County.
The Maine CDC noted that the first case in Maine was from Cumberland County, and the media report on the second case indicated he was from the same area as the first case. Both cases were listed as 8M in the CDC characterization sheet at GISAID and Genbank. These demographics match the 10 participants in the October 1 pig scramble, which was 6 days prior to disease onset for the first case (onset Oct 7 and sample collection Oct 10), and three weeks prior to the second case (onset Oct 22 and sample collection Oct 24).
Therefore, the claim of pig exposure a week prior to disease onset of the second case from Maine is curious.
More detail on the swine exposure dates and source for the second case in Maine, as well as the 6 day gap between swine exposure and onset of symptoms for the first Maine case, would be useful.