The Epidemiology Of Pandemic Influenza A(H1N1) 2009 In China From 2009 To 2010

Background The first influenza pandemic in the 21st century resulted from new pH1N1 influenza virus, which firstly occured in North America in April 2009 On May 10,2009, the first imported human case of Pandemic (H1N1) 2009 was reported in mainland China; then constantly spread. Facing a sudden emergence of infectious diseases, its popular features, harm, High-risk groups.Answers to these questions for all sorts of prevention and control strategy formulation is very important. We described the epidemiology characteristics of the confirmed cases during 2009～2010. It can provide scientific evidence for improving the disease control and prevention measures in mainland China. The existing monitoring system could not monitoring to each case, so to understand the degree of Pandemic (H1N1) 2009 infection in different areas and different age groups, serological survey is necessary.Objectives In order to understand China's trends and the epidemiology characteristics of Pandemic (H1N1) 2009 influenza in the whole country 2009.5.10～2010.7.4. To find out the difference prevalence and risk factors of Pandemic (H1N1) 2009 influenza in different regions and age groups through the serological study, and provide scientific evidence for improving the disease control and prevention measures in mainland China.Methods Pandemic (H1N1) 2009 cases data(2009.5.10～2010.7.4) were obtained from influenza surveillance information management system created by Chinese Center for Disease Control and Prevention. Incidence of Pandemic (H1N1) 2009 influenza were reported by descriptive analysis and using relevant software (Excel, mapinfo. EPI data software,SAS 9.1).A multi-stage random sampling was implemented in 11 provinces. a certain number of respondents polled were extracted in the capital city, small and medium-sized cities and rural,respectively. Questionnaire about basic information and vaccination history was collected. All serum specimens were detected by a hemagglutinin inhibition (HI) test in Chinese National Influenza Center of the Chinese Center for Disease Control and Prevention.Results Between May and August in 2009, Pandemic (H1N1) 2009 cases increased slowly, at the end of August rised fast, August～January of 2010 at peak, November 2009 peak. To September 11,31 provinces all had reported Pandemic (H1N1) 2009 influenza confirmed cases, with most confirmed cases was 5～24 years old(75.75%). The survey enrolled 50111 subjects (unvaccinated:42300;vaccinated:7799). The weighted seroprevalence of pH1N1 was 21.5%(unvaccinated:17.1%; vaccinated:62.0%). Single factor analysis showed that Seroprevalence of 6～15 (32.9%) and 16～24(30.3%) age groups of students and young people was highest, the weighted seroprevalence of pH1N1 in unvaccinated peopleother urban areas was highest(19.6%),Student has the higher the weighted seroprevalence(34.9%) than children in kindergarten (26.2%). The multivariable analysis in unvaccinated people showed that the adjusted odds of seropositivity to pH1N1 infection students (OR:2.045,95%CI:1.643-2.547) and children in kindergarten (OR:1.362,95%CI:1.053-1.761) are higher than children who were in family care. The adjusted odds of seropositivity to pH1N1 infection for the eastern region (OR:0.795,95%CI:0.678-0.932) were statistically lower than that in the western region. There was no statistically significant difference in the odds of infection between the central region (OR:1.026,95%CI:0.891-1.182) and the western region. The odds of pH1N1 infection in the rural areas was statistically significantly lower (OR:0.787,95%CI: 0.685-0.904) compared with the odds of infection in other urban areas. Additionally, our results also showed that there was no statistically significant difference in sex (OR:0.907,95%CI:0.793-1.037),Conclusion Between the end of August in 2009 and the beginning of January in 2010, pH1N1cases rised fast, November 2009 peak. Seroprevalence of 6～15 and 16～24 age groups of students and young people was highest. These groups were a flow control key crowd. After influenza pandemic caused by Pandemic (H1N1) 2009,the weighted seroprevalence of pH1N1 was 21.5%(unvaccinated:17.1%), which reached a high level and indicated that our country crowd had formed certain immune barrier. sero-prevalence of pH1N1 was concerned with age group and occupation and region, and has nothing to do with sex.