Volume 21, Number 1—January 2015
Oseltamivir-Resistant Influenza A(H1N1)pdm09 Viruses, United States, 2013–14
|Method of testing||Neuraminidase inhibitor
|Neuraminidase inhibition assay†|
|No. virus isolates tested‡||1,811||1,811||1,431||352|
|No. oseltamivir susceptible (mean IC50 ± SD, nmol/L)||1,792 (0.19 ± 0.14)||1,811 (0.18 ± 0.06)||1,412 (0.06 ± 0.02)||352 (0.23 ± 0.08)|
|No. oseltamivir resistant, (mean IC50±SD, nmol/L)||19 (181.31 ± 67.63)||0||19 (17.71 ± 6.83)||0|
|No. clinical specimens tested||3,157||NA||3,157||NA|
|No. H275 wild-type||3,117||NA||3,117||NA|
|No. H275 variants||40||NA||40||NA|
|No. virus tested||4,968||1,11||4,588||352|
|No. resistant viruses||59||0||59||0|
*IC50, 50% inhibitory concentration; NA, not applicable.
†H275Y confirmed in virus isolate by pyrosequencing and full neuraminidase sequencing.
‡Most (99.8%) influenza A(H1N1)pdm09 virus isolates were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2013–2014 Northern Hemisphere influenza vaccine.
§Includes pyrosequencing data from New York contract laboratory and data submitted by 19 state public health laboratories in Arizona, California, Colorado, Delaware, Florida, Georgia, Hawaii, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, New York, Pennsylvania, Texas, Utah, Washington, and Wisconsin.
1Members of the 2013–14 US Antiviral Working Group are listed at the end of this article.