title: Does eczema in infancy cause hay fever, asthma, or both in childhood? Insights from a novel regression model of sibling data.
abstract: BACKGROUND
  The atopic march hypothesis proposes that eczema precedes the development of asthma and allergic rhinitis.
  
  
  OBJECTIVE
  We sought to assess the evidence for a causal effect of infantile eczema on childhood hay fever, asthma, or both.
  
  
  METHODS
  We used parental reports on infantile eczema and childhood asthma and hay fever for 3778 pairs of 7-year-olds matched to their sibling closest in age within 2 years from the Tasmanian Longitudinal Health Study. We analyzed paired sibling data using a logistic regression model that allowed inference about a causal effect of a familial predictor on a child's outcome by examining the change in association with their cosibling's predictor after adjusting for their own predictor status.
  
  
  RESULTS
  Siblings were concordant for infantile eczema (tetrachoric correlation, 0.40). For having both hay fever and asthma by age 7 years, the association with cosibling's eczema was an odds ratio (OR) of 1.98 (95% CI, 1.37-2.86), which reduced after adjusting for own eczema to an OR of 1.65 (95% CI, 1.17-2.34). For having hay fever only, the association with cosibling's eczema was an OR of 1.68 (95% CI, 1.22-2.31) before and an OR of 1.59 (95% CI, 1.19-2.14) after adjusting for own eczema. There was no association between having asthma only and cosibling's eczema (OR, 1.00; 95% CI, 0.77-1.30).
  
  
  CONCLUSIONS
  Eczema in infancy might have a causal effect on hay fever in children with and perhaps without asthma. The association of infantile eczema on asthma in children without hay fever, which might be early transient wheeze, is unlikely to be causal or familial. These findings have implications for hay fever prevention.
authors.affiliation: Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, School of Population Health, University of Melbourne, Melbourne, Australia. j.hopper@unimelb.edu.au
authors.forename: John L
authors.initials: JL
authors.lastname: Hopper
authors.forename: Quang M
authors.initials: QM
authors.lastname: Bui
authors.forename: Bircan
authors.initials: B
authors.lastname: Erbas
authors.forename: Melanie C
authors.initials: MC
authors.lastname: Matheson
authors.forename: Lyle C
authors.initials: LC
authors.lastname: Gurrin
authors.forename: John A
authors.initials: JA
authors.lastname: Burgess
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Lowe
authors.forename: Mark A
authors.initials: MA
authors.lastname: Jenkins
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Abramson
authors.forename: E Haydn
authors.initials: EH
authors.lastname: Walters
authors.forename: Graham G
authors.initials: GG
authors.lastname: Giles
authors.forename: Shyamali C
authors.initials: SC
authors.lastname: Dharmage
mesh_terms: D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D002648:Child; D003198:Computer Simulation; D004485:Eczema / Q000150:complications / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D012044:Regression Analysis; D006255:Rhinitis, Allergic, Seasonal / Q000453:epidemiology* / Q000209:etiology; D012307:Risk Factors; D035781:Siblings; D013648:Tasmania / Q000453:epidemiology