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Paradigm Shift Intervention Monitoring
One case of human infection with a
novel influenza A virus was reported by the Pennsylvania Department of
Health. The patient was infected with a swine origin influenza A (H3N2)
virus. The patient reported contact with pigs in the week preceding
symptom onset on September 6, 2010,
Initial testing of the specimen indicated a seasonal influenza A (H3N2) virus and the specimen was submitted to CDC as a routine surveillance sample. The delay from onset to detection occurred because attempts to culture the virus were unsuccessful. RT-PCR testing confirmed swine-origin influenza A (H3N2).
The above comments from today’s week 4 FluView describe a second trH3N2 case in Pennsylvania. The prior case was initially announced with a pager alert for two cases, one from Pennsylvania and an earlier case from Illinois. The CDC subsequently indicated the two cases were from Wisconsin and Pennsylvania. The Wisconsin case developed symptoms two after the unannounced case and six weeks prior to the first announced Pennsylvania case. There has been no sequence released, but it is trH3N2 based on PCR data.
Today’s announcement confirms that trH3N2 cases can type as seasonal H3N2, which is not surprising because trH3N2 has human H3 and human N2. However, these sequences are from infections in the mid-1990’s and the virus has been evolving in swine, so the antigenic drift from contemporary seasonal H3N2 is significant. This drift could lead to an “unsubtypable” result of the condition of the sample is less than ideal. The above comments indicate the latest announced case in Pennsylvania did not culture, raising concerns that the large number of “unsubtypable” isolates reported by Pennsylvania in late 2010 and early 2011 may represent more trH3N2 cases that have not been fully characterized. Pennsylvania leads the nation in reported flu deaths, and several have been reported as H3N2.
The CDC has yet to address the number of trH3N2 under investigation. The close sequence related between the human trH3N2 as well as the presence of PB1 E618D in all recent human cases and its absence in all swine trH3N2 isolates indicates the trH3N2 is transmitting human to human.
The latest case is being reported in 2011, but really represents the four trH3N2 case in the fall of 2010, which is an unprecedented frequency. A pager alert was issued when there were two cases. The latest results indicate there were at least three at the time of the alert, and it remains unclear why one of the cases in the pager alert was said to be from Illinois.
More detail on these cases is long overdue.