H1N1pdm09 Louisiana Tamiflu Resistance Cluster Expands

Wednesday, December 18, 2013
By Paul Martin

December 18, 2013

The CDC has released another series of H1N1pdm09 sequences, which included two more cases with H274Y, signaling Tamiflu resistance. One of those sequences, A/Louisiana/13/2013, from a Louisiana case, 22M, is virtually identical (in all 8 gene segments) to the first 3 Louisiana cases with H274Y (A/Louisiana/07/2013, A/Louisiana/08/2013, A/Louisiana/10/2013). However, unlike the first three cases which were collected in a tight window in October (between October 7 – October 9), the latest sequence is from a November 11 collection, more than a month later, signaling ongoing clonal expansion.

In addition to these four cases in Louisiana, a Mississippi isolate, A/Mississippi/11/2013, which was also collected in November, also has H274Y and is closely related to the Louisiana sequences. These sequences raise concerns that this sub-clone is spreading in the south, where influenza levels are high. The latest CDC FluView reports more than 96% of influenza A cases as H1N1pdm09 (and 94% of influenza is influenza A).

This high level of H1N1pdm09 raises concerns that more middle age cases will be appearing at hospital emergency rooms due to the susceptibility of this age group to H1N1pdm09. In Texas, the Montgomery County Department of Health issued a December 17 press release, citing 8 cases with flu-like symptoms who have tested negative on a rapid test. Four of these cases have died. Media reports indicate the ages of the cases are between 41-68, ages which are susceptible to H1N1pdm09. Moreover, H274Y may have limited treatment, and contributed to the clinical decline of 6 of the 8 cases.

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