A community cluster of influenza A(H1N1)pdm09 virus exhibiting cross-resistance to oseltamivir and peramivir in Japan, November to December 2013

Six influenza A(H1N1)pdm09 viruses were detected in Sapporo, Japan, between November and December 2013. All six viruses possessed an H275Y substitution in the neuraminidase protein, which confers cross-resistance to oseltamivir and peramivir. No epidemiological link among the six cases could be identified; none of them had received neuraminidase inhibitors before specimen collection. The haemagglutinin and neuraminidase genes of the six viruses were closely related to one another, suggesting clonal spread of a single resistant virus.