Oseltamivir-resistant influenza a viruses circulating in Japan.


Surveillance studies of the influenza viruses circulating in Europe and other countries in 2007 and 2008 have revealed rates of resistance to oseltamivir of up to 67% among H1N1 viruses. In the present study, we examined 202 clinical samples obtained from patients infected with H1N1 virus in Japan in 2007 and 2008 for oseltamivir resistance and found that three were oseltamivir resistant (1.5%). The 50% inhibitory concentrations (IC(50)s), as measured by a sialidase inhibition assay with these drug-resistant viruses, were >100-fold higher than those of the nonresistant viruses (median IC(50), 12.6 nmol/liter). The His274Tyr (strain N2 numbering) mutation of the neuraminidase protein, which is known to confer oseltamivir resistance, was detected in these three isolates. Phylogenetic analysis showed that one virus belonged to a lineage that is composed of drug-resistant viruses isolated in Europe and North America and that the other two viruses independently emerged in Japan. Continued surveillance studies are necessary to observe whether these viruses will persist.

DOI: 10.1128/JCM.02396-08

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@article{Tamura2009OseltamivirresistantIA, title={Oseltamivir-resistant influenza a viruses circulating in Japan.}, author={Daisuke Tamura and Keiko Mitamura and Masahiko Yamazaki and Motoko Fujino and Mari Nirasawa and Kazuhiro Kimura and Maki Kiso and Hideaki Shimizu and Chiharu Kawakami and Satoshi Hiroi and Kazuro Takahashi and Mami Hata and Hiroko Minagawa and Yoshiaki Kimura and Satoko Kaneda and Shigeo Sugita and Taisuke Horimoto and Norio Sugaya and Yoshihiro Kawaoka}, journal={Journal of clinical microbiology}, year={2009}, volume={47 5}, pages={1424-7} }