Surveillance and molecular analysis of pandemic A (H1N1) virus in Shandong province of China during the 2009 to 2010 season

The objective of the study was to analyze the epidemiologic, demographic and molecular characteris-tics of pandemic A (H1N1) viruses (A (H1N1) pdm 09) in Shandong Province between May, 2009 and March, 2010. Nasopharyngeal swabs from inuenza-like-illness samples were collected and diagnosed by Real Time RT-PCR method. The positive samples were incubated and cultured in MDCK cells. HA and NA genes of isolated A (H1N1) pdm 09 were sequenced, the homology analysis was done with DNAStar Software and the genetic evolution and amino acid substitutions were performed with Mega 4.0 Software. During the period studied, more than 59% of the positive samples were confirmed A (H1N1) pdm 09 infection. Among them, children aged 5 to 14 and young adults aged 15 to 24 showed to be most susceptible to the A (H1N1) pdm 09 infection, whereas people aged ≥60 years had the lowest rate. There was no substitution of D239G in HA and H275Y in NA, but there was a D204G mutation. In addition, phylogenetic analysis confirmed that the Shandong strains were on different branch with the vaccine strain A/California/07/2009 (H1N1). Constant epidemiological and molecular surveillance is very important to monitor the pathogenicity of circulating strains and evaluate the efficacy of vaccine strain to them.   Key words: Influenza virus, mutation, surveillance.