Abstract
BackgroundAntiviral resistance in Norwegian influenza viruses is rare. Only one A(H1N1)pdm09 virus from May 2015 had been found resistant to oseltamivir since the introduction of these viruses in 2009.ObjectivesSurveillance of antiviral resistance is part of the Norwegian surveillance system, to rapidly detect the development of antiviral‐resistant viruses and spread in the community. We describe the spread of oseltamivir‐resistant A(H1N1)pdm09 viruses in Norway in the 2016‐17 season, found as part of the routine surveillance.MethodsInfluenza H1N1 viruses were analysed for antiviral resistance by pyrosequencing, neuraminidase susceptibility assay and by Sanger sequencing of the HA and NA genes.ResultsDuring the 2015‐16 influenza season, 3% of all A(H1N1)pdm09 viruses screened for resistance in Norway were resistant to oseltamivir, possessing the H275Y substitution in the neuraminidase protein. In comparison, the overall frequency in Europe was 0.87%. Out of these, 37% (n = 10) were reported from Norway. Most cases in Norway were not related to antiviral treatment, and the cases were from several different locations of southern Norway. Genetic analysis revealed that resistant virus emerged independently on several occasions and that there was some spread of oseltamivir‐resistant influenza A(H1N1)6B.1 viruses in the community, characterised by a N370S substitution in the haemagglutinin and T48I in the neuraminidase.ConclusionsOur findings emphasise the importance of antiviral resistance surveillance in the community, not only in immunocompromised patients or other patients undergoing antiviral treatment.
Highlights
Antiviral resistance in Norwegian influenza viruses is rare
Viruses that could not be propagated for NA susceptibility studies were characterised as “amino acid substitution previously associated with highly reduced inhibition” (AAHRI) by the presence of the H275Y substitution
An unusually high percentage of antiviral resistance to oseltamivir was detected in influenza H1N1 viruses from Norway during the 2015‐16 season
Summary
Antiviral resistance in Norwegian influenza viruses is rare. One A(H1N1)pdm[09] virus from May 2015 had been found resistant to oseltamivir since the introduction of these viruses in 2009. Objectives: Surveillance of antiviral resistance is part of the Norwegian surveillance system, to rapidly detect the development of antiviral‐resistant viruses and spread in the community. Results: During the 2015‐16 influenza season, 3% of all A(H1N1)pdm[09] viruses screened for resistance in Norway were resistant to oseltamivir, possessing the H275Y substitution in the neuraminidase protein. Genetic analysis revealed that resistant virus emerged independently on several occasions and that there was some spread of oseltamivir‐resistant influenza A(H1N1)6B.1 viruses in the community, characterised by a N370S substitution in the haemagglutinin and T48I in the neuraminidase. Conclusions: Our findings emphasise the importance of antiviral resistance surveil‐ lance in the community, in immunocompromised patients or other patients undergoing antiviral treatment
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