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PLoS One. 2015 Jan 30;10(1):e0117822. doi: 10.1371/journal.pone.0117822. eCollection 2015.

Molecular surveillance of antiviral drug resistance of influenza A/H3N2 virus in Singapore, 2009-2013.

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Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Department of Laboratory Medicine, National University Hospital, National University Health System, Singapore, Singapore.
Clinical Microbiology, Leicester Royal Infirmary, Leicester, United Kingdom.
Department of Laboratory Medicine, National University Hospital, National University Health System, Singapore, Singapore.
WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, VIC, Australia; Melbourne School of Population and Global Health, University of Melbourne, VIC, Australia.
Department of Pathology, Singapore General Hospital, Singapore, Singapore.


Adamantanes and neuraminidase inhibitors (NAIs) are two classes of antiviral drugs available for the chemoprophylaxis and treatment of influenza infections. To determine the frequency of drug resistance in influenza A/H3N2 viruses in Singapore, large-scale sequencing of neuraminidase (NA) and matrix protein (MP) genes was performed directly without initial culture amplification. 241 laboratory-confirmed influenza A/H3N2 clinical samples, collected between May 2009 and November 2013 were included. In total, 229 NA (95%) and 241 MP (100%) complete sequences were obtained. Drug resistance mutations in the NA and MP genes were interpreted according to published studies. For the NAIs, a visual inspection of the aligned NA sequences revealed no known drug resistant genotypes (DRGs). For the adamantanes, the well-recognised S31N DRG was identified in all 241 MP genes. In addition, there was an increasing number of viruses carrying the combination of D93G+Y155F+D251V (since May 2013) or D93G (since March 2011) mutations in the NA gene. However, in-vitro NAI testing indicated that neither D93G+Y155F+D251V nor D93G alone conferred any changes in NAI susceptibility. Lastly, an I222T mutation in the NA gene that has previously been reported to cause oseltamivir-resistance in influenza A/H1N1/2009, B, and A/H5N1, was detected from a treatment-naïve patient. Further in-vitro NAI testing is required to confirm the effect of this mutation in A/H3N2 virus.

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