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Commentary
Washington
County trH3N2 Cluster Update Fails To Find Source
Recombinomics Commentary 19:00
October 26, 2011
The three cases in Pennsylvania are similar to previous, rare human infections with swine-origin H3N2 viruses, but the infecting strain is unique in that it contains a genetic segment from the 2009 pandemic H1N1 virus. However, the patients experienced typical influenza-like illness.
A continuing investigation, which is being jointly undertaken by the departments of Health and Agriculture, as well as the Centers for Disease Control and Prevention (CDC), has not yet determined how the illness was transmitted to the three individuals.
The above comments are from a September 7 update that was modified October 20. It has some additional detail on the three trH3N2 cases, but fails to identify a source for the three infections, in spite of an investigation the CDC has characterized as “intense”. The failure to find a source for these three cases is similar to the other two trH3N2 cases in 2011 which have the same constellation of flu gene as the three Pennsylvania cases.
The Indiana case has no swine exposure, although his caretaker did. However, like the three Pennsylvania cases, no flu-like symptoms have been identified in human contacts or associated swine, and there have been no reports of SOIV in any human or swine contacts.
Similarly, the constellation of genes found in all five human cases has not been reported in any swine, in spite of enhanced surveillance of swine the United States and the release of sequences from 11 trH3N2 swine isolates in 2011 and 19 additional isolates at the end of 2011 (see list of isolates and collection dates here).
The failure to find a source for the three Pennsylvania case two months after infection, or the Indiana case 3 months after infection again suggest that this unique constellation of genes is transmitting in the human population and the transmission may involve asymptomatic individuals.
These failures, couple with the identities between all five human trH3N2 cases demands a more aggressive screening involving state labs with PCR testing kits that will detect trH3N2 cases.
The distribution of these kits to state labs is long overdue.
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