ABSTRACT
ObjectiveTo understand the detections of influenza A (H1N1) in 2009,and haemagglutinin (HA) gene mutations and the comparisons with standard strains.MethodsThe nasopharyngeal swabs from patients with influenza-like illness (ILI) in National Influenza Sentinel Surveillance Hospital and the outbreak epidemic area were collected.The virus typing and A (H1N1) viruses were tested by real time-polymerase chain reaction (RT-PCR).Then the pathogens were isolated with MDCK cells,the virus titer was determined with hemagglutination test and the virus typing was identified with hemagglutination inhibition test (HA1).The RT-PCR products of HA1 gene of virulent strains were sequenced and then analyzed through bioinformatics.Results A total of 996 pharyngeal swab specimens were tested,and nucleic acid positive cases included 337 A (H1N1) subtype,1 seasonal A (H1N1) subtype,67 A (H3N2) subtype,and 12 B type.The positive rate of nucleic acid detection of influenza was 41.87％ and that of A (H1N1) was 33.84％.Thirty-six influenza A (H1N1) virus strains were isolated,and 10 of them were successfully sequenced and several amino acid mutations were identified.There were 6 amino acid mutations found compared with vaccine strain A/California/07/2009 (H1N1),and 1 site was in area B of epitope.Conclusions A (H1N1) is absolute predominant among isolated strains in 2009.HA gene of virulent strains is mutated compared with vaccine strain provided by World Health Organization,which shows that the area B of epitope changes,while the key amino acid position 222 doesn't change.