title: Serological response in RT-PCR confirmed H1N1-2009 influenza a by hemagglutination inhibition and virus neutralization assays: an observational study.
abstract: BACKGROUND
  We describe the serological response following H1N1-2009 influenza A infections confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR).
  
  
  RESULTS
  The study included patients admitted to hospital, subjects of a seroepidemiologic cohort study, and participants identified from outbreak studies in Singapore. Baseline (first available blood sample) and follow-up blood samples were analyzed for antibody titers to H1N1-2009 and recently circulating seasonal influenza A virus strains by hemagglutination inhibition (HI) and virus micro-neutralization (VM) assays. 267 samples from 118 cases of H1N1-2009 were analyzed. Geometric mean titers by HI peaked at 123 (95% confidence interval, CI 43-356) between days 30 to 39. The chance of observing seroconversion (four-fold or greater increase of antibodies) was maximized when restricting analysis to 45 participants with baseline sera collected within 5 days of onset and follow-up sera collected 15 or more days after onset; for these participants, 82% and 89% seroconverted to A/California/7/2009 H1N1 by HI and VM respectively. A four-fold or greater increase in cross-reactive antibody titers to seasonal A/Brisbane/59/2007 H1N1, A/Brisbane/10/2007 H3N2 and A/Wisconsin/15/2009 H3N2 occurred in 20%, 18% and 16% of participants respectively.
  
  
  CONCLUSIONS
  Appropriately timed paired serology detects 80-90% RT-PCR confirmed H1N1-2009; Antibodies from infection with H1N1-2009 cross-reacted with seasonal influenza viruses.
authors.affiliation: Clinical Epidemiology, Tan Tock Seng Hospital, Singapore, Singapore. Mark_IC_Chen@ttsh.com.sg
authors.forename: Mark I
authors.initials: MI
authors.lastname: Chen
authors.forename: Ian G
authors.initials: IG
authors.lastname: Barr
authors.forename: Gerald C H
authors.initials: GC
authors.lastname: Koh
authors.forename: Vernon J
authors.initials: VJ
authors.lastname: Lee
authors.forename: Caroline P S
authors.initials: CP
authors.lastname: Lee
authors.forename: Robert
authors.initials: R
authors.lastname: Shaw
authors.forename: Cui
authors.initials: C
authors.lastname: Lin
authors.forename: Jonathan
authors.initials: J
authors.lastname: Yap
authors.forename: Alex R
authors.initials: AR
authors.lastname: Cook
authors.forename: Boon Huan
authors.initials: BH
authors.lastname: Tan
authors.forename: Jin Phang
authors.initials: JP
authors.lastname: Loh
authors.forename: Timothy
authors.initials: T
authors.lastname: Barkham
authors.forename: Vincent T K
authors.initials: VT
authors.lastname: Chow
authors.forename: Raymond T P
authors.initials: RT
authors.lastname: Lin
authors.forename: Yee-Sin
authors.initials: YS
authors.lastname: Leo
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000032:analysis / Q000276:immunology; D015331:Cohort Studies; D003429:Cross Reactions; D005260:Female; D006385:Hemagglutination Inhibition Tests / Q000379:methods*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000502:physiology*; D007251:Influenza, Human / Q000175:diagnosis* / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests / Q000379:methods*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral
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