CDC Silence On Spike In trH3N2 Cases Raises Concerns
Recombinomics Commentary 01:15
September 2, 2011

The four cases of novel influenza A virus infection reported to CDC during 2010, and the four cases reported during 2011, were identified as swine influenza A (H3N2) virus….

The above comments are from today’s (week 34) MMWR and include the two cases (PA and IN) reported for this week.  trH3N2 cases are rarely reported for the current week and the report of two cases for the current week is without precedent.  The two cases reported in the week 34 MMWR follows a case reported in week 30.  This case was also from Indiana, and a full sequence, A/Indiana/08/2011, was released by the CDC at GISAID. 

The H3 was similar to recent trH3N2 cases, including two from Minnesota (A/Minnesota/09/2010 and A/Minnesota/11/2010), two from Pennsylvania (A/Pennsylvania/40/2010 and A/Pennsylvania/14/2010), and one from Wisconsin (A/Wisconsin/12/2010).  The sequence was also closely related to two swine isolates (A/swine/North Carolina/A01049436/2011 and A/swine/Indiana/A0109091/2010), including one from Indiana.  However, the human isolate had an MP gene segment from pandemic H1N1, raising concerns that trH3N2 was adapting to transmission in human. 

This concern is increased by the report of two Indiana cases identified in a one month period.  These concerns follow the report that the daughter of the index case in Minnesota was confirmed to have been trH3N2 infected, even though she had no contact with swine.  Moreover, additional family members had influenza symptoms. 

The virus isolated from the index case has been selected as a trH3N2 vaccine target.

However, these recent development have not been addressed at the CDC website for swine originating influenza virus (SOIV) cases in humans.  The site does not include the description of the cluster, the detection of a reassortant in Indiana with a pandemic H1N1 MP gene segment, or the three recently announced cases in Indiana and Pennsylvania.

The report of two cases in Indiana raises transmission concerns, as does the report of current cases in Indiana and Pennsylvania.

Sequences from the two cases announced today, as well as detail on the relationship between the two cases in Indiana and the case in Pennsylvania, would be useful.

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