Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) is sporadic, often follows exposure to NAIs, but occasionally occurs in the absence of NAI pressure. The emergence and global spread in 2007/2008 of A(H1N1) influenza viruses showing clinical resistance to oseltamivir due to neuraminidase (NA) H275Y substitution, in the absence of drug pressure, warrants continued vigilance and monitoring for similar viruses. Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) tested 11,387 viruses collected by WHO-recognized National Influenza Centres (NIC) between May 2012 and May 2013 to determine 50% inhibitory concentration (IC50) data for oseltamivir, zanamivir, peramivir and laninamivir. The data were evaluated using normalized IC50 fold-changes rather than raw IC50 data. Nearly 90% of the 11,387 viruses were from three WHO regions: Western Pacific, the Americas and Europe. Only 0.2% (n=27) showed highly reduced inhibition (HRI) against at least one of the four NAIs, usually oseltamivir, while 0.3% (n=39) showed reduced inhibition (RI). NA sequence data, available from the WHO CCs and from sequence databases (n=3661), were screened for amino acid substitutions associated with reduced NAI susceptibility. Those showing HRI were A(H1N1)pdm09 with NA H275Y (n=18), A(H3N2) with NA E119V (n=3) or NA R292K (n=1) and B/Victoria-lineage with NA H273Y (n=2); amino acid position numbering is A subtype and B type specific. Overall, approximately 99% of circulating viruses tested during the 2012-2013 period were sensitive to all four NAIs. Consequently, these drugs remain an appropriate choice for the treatment and prophylaxis of influenza virus infections.

Influenza virus and respiratory syncytial virus cause acute upper and lower respiratory tract infections, especially in children and the elderly. Early treatment for these infections is thought to be important, so simple and sensitive detection methods are needed for use at clinical sites. Therefore, in this study, real-time reverse transcription loop-mediated isothermal amplification assays with quenching primer for influenza virus and respiratory syncytial virus were developed. Evaluation of a total of 113 clinical specimens compared to real-time RT-PCR assays showed that the novel assays could distinguish between the types and subtypes of influenza virus and respiratory syncytial virus and had 100% diagnostic specificity. The diagnostic sensitivity of each assay exceeded 85.0% and the assays showed sufficient clinical accuracy. Furthermore, positive results could be obtained in around 15 min using the novel assays in cases with high concentrations of virus. The developed assays should be useful for identifying influenza virus and respiratory syncytial virus cases not only in experimental laboratories but also in hospital and quarantine laboratories.