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Is the Pennsylvania trH3N2 Case Unsubtypable?
A nasopharyngeal swab and nasal wash specimen were obtained at the ED and forwarded to the Pennsylvania State Department of Health Bureau of Laboratories for additional testing as part of routine CDC-supported influenza surveillance. On August 23, 2011, the state public health laboratory identified a suspected swine-origin influenza A (H3N2) virus by PCR testing, and both specimens were forwarded to CDC. On August 26, 2011, genome sequencing confirmed the virus as swine-origin influenza A (H3N2). On August 16, 2011, the girl was reported to have visited an agricultural fair where she had direct exposure to swine and other animals. No additional illness in the girl's family or close contacts has been identified, but illness in other fair attendees continues to be investigated.
The above comments from the early release MMWR describe the most recent trH3N2 case (2M) from Schuykill County, Pennsylvania who attended the Washington County agricultural fair.
The above detail indicated she visited an Emergency Department on August 20, 2011, the last day of MMWR week 33. A nasal swab and nasal wash were collected and subsequently tested positive for trH3N2, strongly suggesting that the unsubtypable (unable to subtype) added to the FluView serotype table for week 33 was from the above case.
Prior to this weekend there were no unsubtypables reported by the CDC in its weekly FluView reports since the middle of the 2009/2010 when pandemic H1N1 data was recorded as unsubtypable. The week 33 unsubtypable raises concerns that the trH3N2 in Pennsylvania has evolved further and is no longer recognized by human serotyping reagents, in spite of the human origin of the H3 in trH3N2 from swine. The above case received the 2010 vaccine, which included seasonal H3N2.
If the unsubtypable added this weekend to the CDC serotype table was the Pennsylvania case, trH3N2 has evolved further away from the human H3 sequence. The week 34 FluView noted differences between the trH3N2 case in Indiana and the Pennsylvania case even though both have acquired the pandemic H1N1 M gene segment.
These data raise concerns that the immunity generated against seasonal H3N2 will have limity efficacy against the trH3N2 from Pennsylvania.
More detail on the unsubtypable, and release of the sequences from the Pennsylvania case are overdue.