Oseltamivir-Resistant Seasonal A(H1N1) and A(H1N1)pdm09 Influenza Viruses from the 2007/2008 to 2012/2013 Season in Nara Prefecture, Japan

Abstract

We examined the incidence of oseltamivir-resistant seasonal A(H1N1) and A(H1N1)pdm09 influenza viruses from the 2007/2008 to 2012/2013 season in Nara Prefecture, Japan. To detect the oseltamivir resistance marker in neuraminidase (NA), 365 influenza viruses (60 seasonal A(H1N1) and 305 A(H1N1)pdm09) were sequenced. The H275Y mutation in the NA gene, which confers resistance to oseltamivir, was identified in 93.8% (30/32) of seasonal A(H1N1) viruses that were circulating during the 2008/2009 season. Moreover, the detection rate of oseltamivir-resistant A(H1N1)pdm09 viruses was 4.1% (3/74) and 2.8% (5/180) in the 2009/2010 and 2010/2011 season, respectively. Four cases of oseltamivir-resistant A(H1N1)pdm09 virus infection occurred in the same hematology ward during the 2010/2011 season. Our data show a low frequency of oseltamivir-resistant A(H1N1)pdm09 virus in Nara Prefecture but suggested the possibility of human-to-human transmission of this virus.