title: Seroepidemiological study of influenza A (H1N1) pdm09 virus following the 2009-2010 wave in Shandong Province, China.
abstract: BACKGROUND
  The aims of this study were to understand the geographic extent, risk factors, and attack rate of influenza A (H1N1) pdm09 virus (pH1N1) infection in Shandong Province China and to elucidate influencing factors.
  
  
  METHODS
  In January and March 2010, a cross-sectional seroprevalence survey of pH1N1 was carried out. Serum samples from 9022 participants in the survey were subjected to the hemagglutination inhibition assay.
  
  
  RESULTS
  Among the 9022 participants, the overall rate of seropositivity against pH1N1 was 22.6%. The weighted rate, adjusted for gender, age, and region, was estimated to be 18.7%. Among 8340 subjects who did not report previous vaccination, the rate was 16.7%, as compared to 50.9% among 682 subjects reporting previous vaccination (p < 0.001). Within the unvaccinated population, the rate of seropositivity among 16-24 and 6-15 y-old subjects was 31.8% and 29.9%, respectively, as compared to 9.6% among subjects aged ≥ 60 y (p < 0.001) and 23% in the 0-5 y age group (p < 0.001). Those aged 6-15 y and aged 16-24 y had higher odds of seropositivity than those aged 0-5 y (odds ratio 1.53 and 1.48, respectively).
  
  
  CONCLUSIONS
  These study findings help enhance our understanding of pH1N1 epidemiology and provide valuable information for the vaccination strategy for the influenza season.
authors.affiliation: Shandong Center for Disease Control and Prevention, Shandong Provincial Key Laboratory of Infectious Diseases Control and Prevention, Shandong University Institute for Prevention Medicine, Jinan, Shandong, China.
authors.forename: Ti
authors.initials: T
authors.lastname: Liu
authors.forename: Zhong
authors.initials: Z
authors.lastname: Li
authors.forename: Shaoxia
authors.initials: S
authors.lastname: Song
authors.forename: Shengyang
authors.initials: S
authors.lastname: Zhang
authors.forename: Yulu
authors.initials: Y
authors.lastname: Wang
authors.forename: Lanying
authors.initials: L
authors.lastname: Wang
authors.forename: Aiqiang
authors.initials: A
authors.lastname: Xu
authors.forename: Xianjun
authors.initials: X
authors.lastname: Wang
authors.forename: Zhenqiang
authors.initials: Z
authors.lastname: Bi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral