title: Seroprevalence of pandemic influenza H1N1 in Ontario from January 2009-May 2010.
abstract: BACKGROUND
  We designed a seroprevalence study using multiple testing assays and population sources to estimate the community seroprevalence of pH1N1/09 and risk factors for infection before the outbreak was recognized and throughout the pandemic to the end of 2009/10 influenza season.
  
  
  METHODS
  Residual serum specimens from five time points (between 01/2009 and 05/2010) and samples from two time points from a prospectively recruited cohort were included. The distribution of risk factors was explored in multivariate adjusted analyses using logistic regression among the cohort. Antibody levels were measured by hemagglutination inhibition (HAI) and microneutralization (MN) assays.
  
  
  RESULTS
  Residual sera from 3375 patients and 1024 prospectively recruited cohort participants were analyzed. Pre-pandemic seroprevalence ranged from 2%-12% across age groups. Overall seropositivity ranged from 10%-19% post-first wave and 32%-41% by the end of the 2009/10 influenza season. Seroprevalence and risk factors differed between MN and HAI assays, particularly in older age groups and between waves. Following the H1N1 vaccination program, higher GMT were noted among vaccinated individuals. Overall, 20-30% of the population was estimated to be infected.
  
  
  CONCLUSIONS
  Combining population sources of sera across five time points with prospectively collected epidemiological information yielded a complete description of the evolution of pH1N1 infection.
authors: Department of Surveillance and Epidemiology, Public Health Ontario, Toronto, Ontario, Canada.
authors: Camille
authors: C
authors: Achonu
authors: Laura
authors: L
authors: Rosella
authors: Jonathan B
authors: JB
authors: Gubbay
authors: Shelley
authors: S
authors: Deeks
authors: Anu
authors: A
authors: Rebbapragada
authors: Tony
authors: T
authors: Mazzulli
authors: Don
authors: D
authors: Willison
authors: Julie
authors: J
authors: Foisy
authors: Allison
authors: A
authors: McGeer
authors: Ian
authors: I
authors: Johnson
authors: Marie
authors: M
authors: LaFreniere
authors: Caitlin
authors: C
authors: Johnson
authors: Jacqueline
authors: J
authors: Willmore
authors: Carmen
authors: C
authors: Yue
authors: Natasha S
authors: NS
authors: Crowcroft
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D058873:Pandemics / Q000706:statistics & numerical data*; D012307:Risk Factors; D012621:Seasons; D016036:Seroepidemiologic Studies; D055815:Young Adult