| BackgroundInfluenza, shorten as flu, is an acute respiratory communicable disease caused by influenza viruses. It usually characterizes with short incubation period. high infectivity and rapid spread. Influenza viruses divided into three types—type A,B and C. Influenza A virus is more likely to cause wide prevalence, even across countries, or continents, which always with great damage. Influenza B virus usually causes limited circulation and most type C-caused influenza is sporadic.Influenza is the first international surveillance communicable disease, and currently influenza centers of more than 110 nations and regions have constituted the global influenza surveillance network. China initiated influenza surveillance in 1952, and now has built an influenza surveillance network covered 23 provinces which mainly based on influenza-like illness (ILI) report and virus isolation. Through the smooth implementation of this cooperative program, the integration level of our nation's influenza surveillance has been significantly improved, but it still faces challenges when coping with the occurrence of influenza pandemic because of unbalanced capacity between different regions. In 2005, Ji'nan began to assume the responsibility of influenza surveillance and it could basically reflect the prevalence trend in our city. However, there's bias existed when comes to surveillance outcome, because each stage could be influenced by many factors. What's the result of influenza surveillance of Ji'nan during 2005-2009, what's the variant trend of virus strains, and could current surveillance network be sufficient to cope with influenza pandemic, all of these should be discussed here.In March 2009, there're "Novel influenza A (H1N1)" outbreaks in America and Mexico. Now novel influenza A (H1N1) has spread widely and current reported confirming cases could not reflect the true incidence status because of the existence of mass mild and sub-clinical cases. What's the infection rate of Novel influenza A (H1N1) in Ji'nan, which population group is more likely to be infected? Aiming at Novel influenza A (H1N1) prevalence in 2009, under the circumstance of lack of Novel influenza A (H1N1) antibody surveillance studies in China, we need to learn about the influenza infection level among people in different age groups and different regions, so as to provide scientific references for disease control and prevention.Objectives1. Describe the seasonal distribution features of seasonal flu and the prevalent trend of virus strains of Ji'nan during 2005-2009.2. Describe the epidemiology of Novel influenza A (H1N1) prevalence of Ji'nan in 2009, test Novel influenza A (H1N1) antibody levels of healthy population of Ji'nan in 2010 so as to master the infection status of Novel influenza A (H1N1) among the whole population, then provide theory reference for policy making of Novel influenza A (H1N1)control strategies and measurements.Methods1. Descriptive analysis based on influenza-like illness (ILI) surveillance data from sentinel hospitals, etiologic test results of reported cases and information about flu outbreaks in Ji'nan, during 2005-2009. Hospital visit ratio of influenza-like illness (ILI) and toxic strain positive rate was calculated. Analyze the annual prevalence trend and variation status of prevalence strains.2. Through description study, analyze seasonal, regional and population distribution of Novel influenza A (H1N1) of Ji'nan in 2009, explore and discuss the epidemiologic features so as to provide theory support for coping with Novel influenza A (H1N1) pandemic.3. Multi-stage stratified randomized sampling was applied in this study; three cross-sectional studies were carried out in Lixia, Huaiyin and Licheng district of Ji'nan in Jan, Mar and Aug,2010. Healthy population such as scattered children, kindergarten children, students, teachers, healthcare workers were chosen to collect serum specimens for Novel influenza A (H1N1) antibody tests at different seasons and different regions.Results一. Influenza surveillancel.From Oct 2005 to Apr 2009, there were 13,731 cases reported as influenza-like illness (ILI) from 4 influenza sentinel hospitals, and the hospital visiting ratio was 2.24%.2.From Oct 2005 to Apr 2009, nasopharyngeal swab specimens were collected by 4 influenza sentinel hospitals and the positive rate was 21.74%. According to virus isolation results, it showed continuous variations in circulating strains—among all positive specimens,115(29.87%) belongs to seasonal influenza Al,169(43.90%) influenza A3, 1(0.26%) un-typed influenza A,28(7.27%) belongs to the B/Victoria lineage,65(16.88%) belongs to the B/Yamagata lineage,7 (1.82%) was un-typed influenza B.3.There were 25 ILI outbreaks reported in Ji'nan during 2005-2009 and the annual outbreak related predominant strains were different. The influenza activity peak was focusing in winter and next spring each year.二. Novel influenza A (H1N1) epidemic460 Novel influenza A (H1N1) confirmed cases were reported in 2009, including 60 with serious complications,11 ICU admissions,4 deaths and no pregnancy death. The whole population of Ji'nan was 6,156,678 and the Novel influenza A (H1N1) morbidity rate was 7.47/100,000, the mortality rate was 0.06/100,000, and the fatality rate was 0.87%.三. Investigation on Novel influenza A (H1N1) infection status1.Three cross-sectional sampling investigations on Novel influenza A (H1N1) infection status were carried out in Lixia, Huaiyin and Licheng district of Ji'nan in Jan, Mar and Aug 2010, respectively.4613 serum specimens were collected and the positive rate was 31.78%, which was a little higher than the national average level—23.00%.2.1555 were collected in January with a positive rate of 34.53%,1500 were collected in March with a positive rate of 27.07%,1558 were collected in August with a positive rate of 33.57%.3.1500 specimens were collected by Lixia district with a positive rate of 32.93%, 1500 specimens were collected by Huaiyin district with a positive rate of 28.07%,1613 specimens were collected by Licheng district with a positive rate of 34.35%; positive rate in age 0-5yrs was 42.95%, age 6-15yrs was 40.70%,16-24yrs was 46.44%,25-59yrs was 13.87%, and≥60yrs was 14.21%; positive rate in children(kindergarten and scattered) was 38.26%, students was 42.46%, teachers, healthcare workers and other occupation population was 45.24%,33.33% and 21.36%.Conclusions1. Influenza surveillance in Ji'nan during 2005-2009 showed that ILI doctor visiting ratio variation trend was almost the same in each year. ILI circulating peak mainly focused in November and next January. Active influenza strains among population were A1/H1N1, A3/H3N2, B/Yamagata lineage, and B/Victoria lineage.2. Predominant strains of each year were different. Predominant strain during 2005—2006 was A1 subtype,2006—2007 was A3 subtype,2007—2008 were A3 subtype and B/Yamagata lineage,2008—2009 was A1 subtype and Novel influenza A (H1N1) was the predominant strain of influenza prevalence season in 2009.3. ILI prevalence peak was accord with peak of influenza strain positive detections. Influenza strain variation trend showed that circulating strains causing spring outbreaks would become the predominant strains of that winter.4. Novel influenza A (H1N1) was in a relatively low level in 2009.5. Infection rates among population groups were different.6.Novel influenza A (H1N1) infection rate was relatively low in Ji'nan and population immunological barrier should be established through influenza vaccination. |
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