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CDC Hiding trH3N2 Cluster In Minnesota
Recombinomics Commentary 10:50
September 3, 2011

Although no person-to-person transmission of swine influenza viruses has been laboratory confirmed in the investigation of these cases to date.....

The above comment is from the CDC website designed to present information on and links to swine influenza cases in humans, as indicated by the title “Reported Human Infections with Swine Origin Influenza Viruses (SOIV) in the United States since 2005”.  The page provides a background on triple reassortants (tr) in humans including trH1N1, trH1N2, and trH3N2.  All reported cases since mid-2009 have been trH3N2, and the background paragraph, which was update in early 2011 details cases reported, as of 2010.  More recent cases are added via links to CDC publications such as “Have you heard” or periodic MMWR updates.  The linked MMWR updates have a section on novel influenza cases which details the cases reported / confirmed in the time frame covered by the update.

Thus, the site was updated yesterday with a link to the early MMWR description of the trH3N2 cases in Indiana and Pennsylvania.  However, the glaring omission in the MMWR updates is the June 3, 2011 report (week 21) entitled Update: Influenza Activity --- United States, 2010--11 Season, and Composition of the 2011--12 Influenza Vaccine. 

The novel influenza section of this update details the trH3N2 cluster in Minnesota and clearly states lab confirmation of H3N2 in the daughter of the index case who did not have swine contact “The child, whose infection with influenza A (H3N2) virus was confirmed several weeks later by serologic testing, did not have direct swine exposure, and most likely acquired infection from close contact with her father.”

This cluster was a concern because in addition to the lab confirmed H3N2 in the index case and his daughter, additional family members had influenza-like illness.  The confirmation of the H3N2 in the daughter led to a week 30 MMWR update which raised the number of trH3N2 cases reported in 2011 to 2 (although both cases were due to infections in 2010), and the CDC has used the isolate from the father, A/Minnesota/11/2010, as a pandemic H3N2 vaccine target.

Thus, although this cluster is detailed in the week 21 MMWR and the confirmation of the daughter is used to increase the number of trH3N2 cases in the week 30 report, and the H and N genes from the index case was used to create a reassortant on a PR-8 genetic background (PR-8 is the genetic background used in influenza vaccines), there is no linkage of this 2010 cluster on the CDC website linking cases confirmed since 2005.

Moreover, none of the recent agency affiliated quotes in the media reports on the two recent trH3N2 cases in Indiana and Pennsylvania (listed in MMWR week 34 report)mention this cluster or the testing of the pandemic H3N2 target, even though the H3 sequence from Minnesota (A/Minnesota/11/2010) is closely related to the sequence from the Indiana case (A/Indiana/08/2011), as well as 2010 cases from Minnesota (A/Minnesota/09/2010),  Wisconsin (A/Wisconsin/12/2010), and Pennsylvania (A/Pennsylvania/40/2010 and A/Pennsylvania/14/2010) and presumably the 2011 Pennsylvania case since the isolate also has an MP gene segment from the 2009 pandemic H1N1 clade.

The CDC should immediately update its website with information on the Minnesota cluster and removal of the claim that there has been no lab confirmation of human transmission of trH3N2.

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