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Paradigm Shift Intervention Monitoring
Washington Fair trH3N2 Cluster Signals Human
The cases in Pennsylvania are similar to previous, rare human infections with swine-origin H3N2 viruses, but are unique in that they contain a genetic component of the H1N1 virus.
The above comments from a Pennsylvania Department of Health press release describe two additional confirmed trH3N2 cases at the Washington County Fair. Like the earlier case in Indiana, A/Indiana/08/2011, and the previously reported case from Schuykill County, PA, who attended the above fair, the two new cases had the H1N1 M gene segment, which is linked to aerosol spread in a guinea pig model of human influenza transmission.
These cases increase the Pennsylvania total of confirmed cases to five, including three 2011 cases with the M gene segment. The three confirmed cases represent the largest number of confirmed trH3N2 cases at a given location, and the investigation is still ongoing.
The press release does not clarify the severity of the infection in the two most recent cases, who may have been ill for nore than two weeks (the fair ended August 20). Hospitalization was not addressed in the press release, but the four cases with H1N1 M1 appear to be serious enough to warrant emergency department visits.
It is likely that these three cases represent unsubtypable trH3N2 which is not recognized by the human H3 serotyping reagents, suggesting existing immunity to seasonal H3N2 will provide limited protection.
Additional cases are under investigation, but this cluster strongly supports human to human transmission of a novel trH3N2 with a pandemic H1N1 M gene segment.
The unsubtypable cases will be more easily identified by state labs, and an explosion of confirmed cases is expected.
Release of the sequences from the first PA case is overdue.