Molecular epidemiology and phylogenetic analysis of HA gene of influenza A(H1N1)pdm09 strain during 2010-2014 in Dalian, North China

The objective of the present study was to evaluate the epidemiology of influenza A(H1N1)pdm09 and its hemagglutinin (HA) molecular and phylogenetic analysis during 2010-2014 in Dalian, North China. A total of 3717 influenza-like illness (ILI) cases were tested by real-time PCR and 493 were found to be positive. Out of these 493 cases, 121 were subtype influenza A(H1N1)pdm09, of which 14 cases were reported in 2010-2011, 29 in 2012-2013, and 78 in 2013-2014. HA coding regions of 45 isolates were compared to that of the vaccine strain A/California/7/09(H1N1), and a number of variations were detected. P83S, S185T, S203T, R223Q, and I321V mutations were observed in all of the Dalian isolates. Furthermore, a high proportion > 71 % of the strains possessed the variation D97N and K283E. Phylogenetic analysis confirmed the close match of the majority of circulating strains with the vaccine strains. However, it also reveals a trend of strains to accumulate amino acid variations and form new phylogenetic groups.