H1N1 influenza surveillance in Ningbo city, 2004-2008

Objective To understand the trend of influenza epidem is and to explore the variation of the viruses isolated.Methods Surveillance sites were established Data of influenza-like illness(ILI%)was collected and analyzed Throats wab and gargling specie ens collected from influenza-like cases were isolated with MDCK cells and embryonated eggs aged 9-11 days.Results A total of 99 333 influenza-like illnesses were reported from 2004 to 2008,accounted for 4.49%(99 333/2 210 318) of the total outpatients,with 5 784 specie ens collected and 686 virus isolated Among the virusisolation,there were 163 cases of influenza H1N1 virus,492 cases of influenza H3N2 virus,and 31 cases of influenza B Victoria virus The average isolation rate of influenza virus was 11.86%(4.14%-22.32%).The epidemis of influenza was seasonal with two peaks of LI% in the end of spring(March and April) and the beginning of autumn(A ugust and September).When comparing amino acid sequences of HA1 protein domain of H1N1 vimses isolated in 2006 with those of NewCaledonia/20/1999(H1N1)vinrs,it was revealed that there were 7 differences in amino acid sequences bettyeen them.There were 6 differences in amino acid sequences of HA1 protein domain bettyeen H1N1 vimses isolated in 2008 and Bribane-59-2007(H1N1) vims.Conclusion The change of LI% is associated with influenza vims variation The mutation of H1N1 is active