H1N1pdm09 Louisiana Tamiflu Resistance Cluster

Wednesday, November 20, 2013
By Paul Martin

November 19, 2013

The CDC has released a series of H1N1pdm09 sequences from the current season, which included two sets if sequences from Louisiana, which had H274Y, signaling Tamiflu (oseltamivir) resistance. A sample from one case (25F), A/Louisiana/07/2013, was collected on October 7, which was followed by another case (56F), A/Louisiana/08/2013, which was collected on October 9. The relationship between these two cases is unknown, but the virtual identity for all 8 gene segments indicates this sub-clade is spreading via clonal expansion.

In the week 43 FluView, the CDC reported testing on 28 H1N1pdm09 during the 2013/2014 and none were Tamiflu resistant. However, in week 44 nine additional samples were tested, and two were resistant, strongly suggesting that the two examples were the two cases described above. In week 45 the CDC reported one more case of resistance, but those sequences have not been released, so the relationship to the above two cases is unknown.

The sequence similarity between the first two cases signals evolutionary fitness for this sub-clade. More information on the status and relationship of these two cases to each other and the third case, reported in week 45, would be useful.

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