Surveillance Of Influenza Like Illness And Variation Analysis Of HA And NA Gene For Isolated Influenza Viruses In Yunnan Province During 2009-2014

ObjectivesThe data of influenza like illness (ILI) surveillance from 2009 to 2014 in Yunnan province were analyzed; a prediction model of ILI was constructed to forecast the trend of the distribution of ILI in 2015. The variation of HA and NA gene for isolated influenza viruses in Yunnan Province during 2009-2014 were analyzed to provide information for the vaccination and treatment of influenza, early warning and prediction of influenza epidemic.MethodDescriptive method was employed to analyze the surveillance data of ILI which were reported from 19 sentinel hospitals located in 16 prefectures of Yunnan province from 2009 to 2014. Mathematical model was created by using expert modeling method to predict the epidemic trend of ILI in 2015. The viral RNA was extracted from 64 influenza viruses isolated in Yunnan province during 2009-2014, the viruses include 25 H3N2 subtype strains,23 A/pdmHlNl subtype and 12 B strains. The HA and NA gene of influenza virus were amplified with specific primer by applying RT-PCR. The products of amplification were purified. The sequences of HA and NA gene for influenza viruses were determined. The sequences of epidemic strains in Yunnan province with reference and vaccine strains were put together to produce gene tree for evolution analyses. Software SPSS 17.0 was used for the statistical analysis of data. DNASTAR was for shear and splicing of HA and NA gene. MEGA5.1 was employed for creating evolutionary trees.ResultDuring 2009-2014,17308285 patients and 358314 ILI cases were reported from the outpatient department of 19 sentinel hospitals which are located in 16 prefectures; the proportion of ILI cases in total out-patient was 2.07%. There was a high ILI%in Baoshan, Kunming and Honghe prefecture distributed. The proportion of ILI in 0-15 age group was more than 60% in the total number of ILI cases. The rate of influenza viruse isolation was increased year by year in Yunnan province. H3N2 subtype, A/pdmH1N1 subtype and B appeared in different season during 2009-2014 alternately and became dominant strains in different season. The epidemic trend of ILI in 2015 was predicted by using the predicting model, the results show that epidemic trend of ILI in 2015 will be stable as a whole; there may be some fluctuation in limited scope.The results of HA and NA gene sequencing analysis for the influenza viruses isolated in Yunnan province during 2009-2014 show that the affinity and the homology of each subtype presented the time distribution characteristic in the gene tree. Except for a strain isolated during 2009-2014 with special molecular markers of variation, the obvious variation had not been found in all the rest. On the basis of the results of NA sequence analysis, emergence and changes of a significant drug resistance loci had not been found in the all strains, they are still sensitive to neuraminidase inhibitors used in clinical at present.Conclusion1. According to the data analysis of ILI surveillance and the trend forecast of ILI prevalence, the trend of ILI prevalence in Yunnan province will be stable recently, a wide range change are less likely.2. The HA and NA gene sequences of prevalence strains isolated in Yunnan province during 2009-2014 had not obvious variation.3. There is good matching between vaccine strains used in China and prevalence strains in Yunnan province currently, the influenza vaccines currently used in Yunnan province have a better protective effect for the human influenza prevention after vaccination.4. The prevalence strains isolated in Yunnan province during 2009-2014 are still sensitive to neuraminidase inhibitors used in clinical treatment currently.