Characterization of human Influenza Viruses in Lebanon during 2010-2011 and 2011-2012 post-pandemic seasons.

OBJECTIVE: To genetically characterize human influenza viruses and their susceptibilities to antivirals during two post-pandemic seasons in Lebanon.

METHODS: Influenza virus was isolated from nasopharyngeal swabs that were obtained from patients with influenza-like illness during 2010-2012 and further analyzed both phenotypically and genotypically.

RESULTS: During the 2010-2011 season, both 2009 pandemic H1N1 (H1N1p) and B viruses co-circulated with equal prevalence, while the H3N2 virus predominated during the 2011-2012 season. All H3N2 and H1N1 viruses were resistant to amantadine. Importantly, all viruses of the influenza A and B types were susceptible to the neuraminidase (NA) inhibitors oseltamivir, zanamivir, peramivir, and laninamivir. Nonetheless, all 2011-2012 H1N1p isolates had three mutations (V241I, N369K, and N386S) in the NA gene that were suggested to be permissive of the H275Y mutation, which confers resistance to oseltamivir. We also detected one H1N1p virus during the 2010-2011 season with a 4-fold decrease in susceptibility to oseltamivir due to an NA-S247N mutation. This isolate was phylogenetically distinct from other H1N1p viruses that were isolated in other regions.

CONCLUSIONS: Influenza A viruses with reduced susceptibility to oseltamivir and mutations permissive for acquiring NA resistance-conferring mutation with minimal burden on their fitness were isolated in Lebanon.