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Commentary
CDC Describes
11 Hospitalized H3N2v Cases In Ohio
Recombinomics
Commentary 19:15
September 27, 2012
The above comments are from a CDC MMWR report, “Influenza A (H3N2) Variant Virus-Related Hospitalizations — Ohio, 2012” which provides some detail on 11 H3N2v infected Ohio patients who visited agricultural fairs and were subsequently hospitalized. The adult mention above is the only reported fatal H3N2v case (61M) and the sample collection date of August 25, 2012 matches the isolate A/Ohio/74/2012 which is closely related to multiple human and swine cases including Ohio and Wisconsin cases with an identical H3 (A/Ohio/75/2012, A/Ohio/64/2012, A/Wisconsin/22/2012, A/Wisconsin/23/2012, A/Wisconsin/27/2012, A/swine/Ohio/12TOSU447/2012, A/swine/Ohio/12TOSU450/2012.
However, the report focused on swine exposure and ignored the large number of human H3N2v cases at these fairs. The report failed to name the six fairs or eight counties, although media reports indicated the fatal case (61F) attended the Ross County Fair and live in London, Ohio which is the county seat for Madison County. Similarly media reports cited a Lake County case without swine exposure, which matches case #10 who developed symptoms on August 25, which was in the same time frame as the media reports and the Ohio Department of Health’s addition of a Lake County case.
In addition to the case with no swine exposure, 4 additional cases had “indirect” exposure, and one of the direct exposure cases developed symptoms 6 days after exposure suggesting most of the cases were not infected by swine. Moreover, as cited above, only one of the cases with direct exposure “might” have had contact with a symptomatic swine.
Although only one of the 11 cases might have had contact with a symptomatic swine, it is likely that the vast majority had contact with symptomatic people who attended the fairs. Details of the number of symptomatic cases at these fairs are limited because of the CDC heavy bias toward swine transmission (and corresponding lack of information on the number of symptomatic cases at the fairs), but reports from Gallia County in southeastern Ohio indicated the local department of health ran rapid test on 200 symptomatic attendees and 69 were influenza A positive, suggesting virtually all 200 were symptomatic because of an influenza A infection (the sensitivity of raid tests for H3N2v is in the 30-40% range). Moreover, ODH reported 12 confirmed H3N2v cases from Gallia County, while the West Virginia reported 3 confirmed H3N2v from residents who attended the Gallia Junior County Fair. In addition, many additional symptomatic attendees were not tested, indicating hundreds of attendees were H3N2v infected. Similarly, other counties (Butler and Champaign) reported higher numbers of confirmed cases than Gallia.
The large number of human cases at these fairs was not limited to Ohio. In Indiana, Monroe County reported 61 H3N2v confirmed cases.
These large numbers of symptomatic / H3N2v confirmed cases were also seen last year. An early release of a December EID paper on the 2010 Washington County Fair outbreak described serological and phone surveys of a subset of 4-H Club attendees. Earlier reports had described the 3 H3N2v confirmed cases, but the serological studies identified 4 additional probable cases with H3N2v antibodies, as well as 82 symptomatic cases. Moreover, since only 1/3 of the 4-H Club attendee list was called (247/994 members), and 127 of those contacted agreed to be interviewed, the number of symptomatic cases linked to the 4-H Club was likely in the hundreds. No H3N2v infected swine were identified at the fair and only one swine was symptomatic (and removed after 1 day). Moreover, none of the thirteen 2011 or twenty 2012 swine matches for the 2011/2012 H3N2v cases were from Pennsylvania.
Thus, there is little evidence to support extensive swine to human transmission at the 2011 or 2012 agricultural fairs. Although the genetic matches with the 2011 H3N2v cases are widespread in swine, including Ohio and Indiana isolates, no 2012 matching human H3N2v case has been reported. All 2012 human cases match a novel H3N2v sub-clade which was first detected at a West Virginia day care center in late 2011.
However, in spite of these match failures, the CDC continues to focus on swine to human transmission, and ignores the human to swine and human to human transmission at agricultural fairs.
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