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Volume 17, Number 3—March 2011


Monitoring and Characterization of Oseltamivir-Resistant Pandemic (H1N1) 2009 Virus, Japan, 2009–2010

Makoto Ujike, Miho Ejima, Akane Anraku, Kozue Shimabukuro, Masatsugu Obuchi, Noriko Kishida, Xu Hong, Emi Takashita, Seiichiro Fujisaki, Kazuyo Yamashita, Hiroshi Horikawa, Yumiko Kato, Akio Oguchi, Nobuyuki Fujita, Masato Tashiro, Takato OdagiriComments to Author , and the Influenza Virus Surveillance Group of Japan
Author affiliations: Author affiliations: National Institute of Infectious Diseases, Tokyo, Japan (M. Ujike, M. Ejima, A. Anraku, K. Shimabukuro, M. Obuchi, N. Kishida, X. Hong, E. Takashita, S. Fujisaki, K. Yamashita, M. Tashiro, T. Odagiri); National Institute of Technology and Evaluation, Tokyo (H. Horikawa, Y. Kato, A. Oguchi, N. Fujita)

Main Article

Table 3

Summary of neuraminidase inhibition assay of oseltamivir-resistant and oseltamivir-sensitive pandemic (H1N1) 2009 virus to oseltamivir and zanamivir*

Strain IC50, (nM/L)
No. isolates Mean ± SD (range) Cutoff value No. isolates Mean ± SD (range) Cutoff
Pandemic (H1N1) 2009
Oseltamivir-sensitive 421 0.10 ± 0.02 (0.05–0.19) >0.20 421 0.28 ± 0.06 (0.11–0.61) >0.60†
37.28 ± 14.06 (20.69–80.91)

0.36 ± 0.11 (0.17–0.64)

Seasonal influenza (H1N1) (A/Yamagata/41/2008)
Oseltamivir-sensitive 0.09 ± 0.02§ 0.24 ± 0.10
Oseltamivir-resistant 51.76 ± 9.54 0.37 ± 0.13

*IC50, 50% inhibitory concentration; NC, not calculated.
†Because both IC50 values of OS and OR pandemic (H1N1) 2009 viruses were indistinguishable, the cutoff values for zanamivir were calculated from the overall population (N = 482).
‡IC50 values of 13 mixed samples with H275 and Y275 were excluded from overall population in statistical analysis of OR isolates.
§Mean ± SD IC50 values of control seasonal influenza A (H1N1) viruses were determined from 10 independent experiments for oseltamivir and 2 for zanamivir.

Main Article

1Members of the Influenza Virus Surveillance Group of Japan are listed at the end of this article.

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