ABSTRACT
To determine the etiologic agent of an outbreak of influenza viruses from Changsha Foothill Mountain International School in 2009, and to analyze the HA Gene Characteristic of the H1N1 influenza viruses. Twenty-five nasopharyngeal swab specimens from the outbreak of influenza viruses were tested by conventional RT-PCR and influenza viruses isolated simultaneously. Virus isolated (A/Yuelu/314/2009) from the outbreak was sequenced by CEQTM 8000 Genetic Analysis System and the sequencing results submitted to GenBank (Accession No: FJ912843), then the sequencing data was analyzed by ClustalX and Mega4.1softwares. Results showed the influenza viruses A(H1N1) of positive were 18 cases by influenza viruses isolated tests and 21 cases by conventional RT-PCR, respectively. The nucleotide and amino acid sequence homology of the HA gene of A/Yuelu/314/2009 are 99% compare with the vaccine strain (A/Brisbane/59/2007) in 2008~2009 years. The HA sequence data also showed that had 6 amino acid mutations (V148A, S158N, G202A, I203D, A206T, W435R), and the S158N located at antigenic site B of HA protein. Nine potential glycosylation sites (27, 28, 40, 71, 151, 176, 303, 497, 536) in the HA sequence of A/Yuelu/314/2009 is the same with A/Brisbane/59/2007, and the sequences of potential glycosylation sites were conserved. In this study, laboratory evidence diagnosed seasonal influenza A virus (H1N1) as the etiologic agent of the outbreak. The virus isolated (A/Yuelu/314/2009) strain of H1N1 subtype is not a new variant in Changsha in 2009 compare with the vaccine strain (A/Brisbane/59/2007), the outbreak of influenza A virus (H1N1) from Changsha Foothill Mountain International School maybe are caused by the change in genetic characteristics between vaccine strains and the decreased of immunity to influenza A virus (H1N1) in the crowd.