title: Estimated cumulative incidence of pandemic (H1N1) influenza among pregnant women during the first wave of the 2009 pandemic.
abstract: BACKGROUND
  Hospitalization and lab confirmed cases of H1N1 have been reported during the first wave of the 2009 pandemic but these are not accurate measures of influenza incidence in the population. We estimated the cumulative incidence of pandemic (H1N1) influenza among pregnant women in the province of Manitoba during the first wave of the 2009 pandemic.
  
  
  METHODS
  Two panels of stored frozen serum specimens collected for routine prenatal screening were randomly selected for testing before (March 2009, n = 252) and after (August 2009, n = 296) the first wave of the pandemic. A standard hemagglutination inhibition assay was used to detect the presence of IgG antibodies against the pandemic (H1N1) 2009 virus. The cumulative incidence of pandemic (H1N1) influenza was calculated as the difference between the point prevalence rates in the first and second panels.
  
  
  RESULTS
  Of the specimens collected in March, 7.1% were positive for the IgG antibodies (serum antibody titre ≥ 1:40). The corresponding prevalence was 15.7% among the specimens collected in August. The difference indicated a cumulative incidence of 8.6% (95% confidence interval [CI] 3.2%-13.7%). The rate differed geographically, the highest being in the northern regions (20.8%, 95% CI 7.9%-31.8%), as compared with 4.0% (95% CI 0.0%-11.9%) in Winnipeg and 8.9% (95% CI 0.0%-18.8%) in the rest of the province.
  
  
  CONCLUSIONS
  We estimated that the cumulative incidence of pandemic (H1N1) influenza among pregnant women in Manitoba during the first wave of the 2009 pandemic was 8.6%. It was 20.8% in the northern regions of the province.
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, Man. salah.mahmud@gmail.com
authors.forename: Salaheddin M
authors.initials: SM
authors.lastname: Mahmud
authors.forename: Marissa
authors.initials: M
authors.lastname: Becker
authors.forename: Yoav
authors.initials: Y
authors.lastname: Keynan
authors.forename: Lawrence
authors.initials: L
authors.lastname: Elliott
authors.forename: Laura H
authors.initials: LH
authors.lastname: Thompson
authors.forename: Keith
authors.initials: K
authors.lastname: Fowke
authors.forename: Lisa
authors.initials: L
authors.lastname: Avery
authors.forename: Paul
authors.initials: P
authors.lastname: Van Caeseele
authors.forename: Sande
authors.initials: S
authors.lastname: Harlos
authors.forename: James
authors.initials: J
authors.lastname: Blanchard
authors.forename: Magdy
authors.initials: M
authors.lastname: Dawood
mesh_terms: D000293:Adolescent; D000328:Adult; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D008350:Manitoba / Q000453:epidemiology; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000453:epidemiology*; D011295:Prenatal Care; D016036:Seroepidemiologic Studies
chemical_list: D007074:Immunoglobulin G
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