Oseltamivir-resistant influenza A(H1N1)pdm09 viruses, United States, 2013-14

Abstract

We report characteristics of oseltamivir-resistant influenza A(H1N1)pdm09 viruses and patients infected with these viruses in the United States. During 2013-14, fifty-nine (1.2%) of 4,968 analyzed US influenza A(H1N1)pdm09 viruses had the H275Y oseltamivir resistance-conferring neuraminidase substitution. Our results emphasize the need for local surveillance for neuraminidase inhibitor susceptibility among circulating influenza viruses.

Figure 1

Geographic distribution of oseltamivir-resistant influenza A(H1N1)pdm09 viruses, United States, 2013–14. Gray indicates the presence of an oseltamivir-resistant virus. Number of oseltamivir-resistant A(H1N1pdm)09 viruses divided by total number of viruses tested is shown for each state. Oseltamivir-resistant A(H1N1)pdm09 viruses were significantly more prevalent in Louisiana (LA) (p = 0.04, by Fischer 2-sided exact test), Pennsylvania (PA) (p<0.001), Mississippi (MS) (p = 0.02), Hawaii (HI) (p = 0.02), and California (CA) (p = 0.03) than in all other states combined.

Figure 2

Evolutionary relationships among influenza A (H1N1)pdm09 virus neuraminidase genes, United States, 2013–14. Phylogenetic tree was generated by using MEGA software v5.2 (http://www.megasoftware.net/) and the neighbor-joining method. Evolutionary distances were computed by using the maximum composite likelihood model. Analysis included 100 representative A(H1N1)pdm09 neuraminidase gene sequences. Scale bar indicates nucleotide substitutions per site. Solid circles indicate oseltamivir-resistant H275Y markers. A/California/07/2009 (current Northern Hemisphere vaccine strain) virus was used as a reference for ancestry (root) and numbering. F, Centers for Disease Control and Prevention reference antigen; Oct, October 2013; Nov, November 2013; Dec, December 2013; Jan, January 2014; Feb, February 2014; GLY, glycosylation.