title: Evidence of a causal role of winter virus infection during infancy in early childhood asthma.
abstract: BACKGROUND
  Bronchiolitis during infancy is associated with an increased risk of childhood asthma. Whether winter viral infections cause asthma or are a manifestation of a predisposition to asthma development is unknown.
  
  
  OBJECTIVE
  To study the relationship of winter virus infection during infancy and the development of childhood asthma.
  
  
  METHODS
  We studied over 95,000 infants born between 1995 and 2000 and followed through 2005 who were enrolled in the Tennessee Medicaid program from birth through early childhood to determine whether infant birth in relationship to the winter virus peak alters the risk of developing early childhood asthma.
  
  
  RESULTS
  Among 95,310 children studied during five winter virus seasons from birth through early childhood, the risk of developing asthma tracked with the timing of infant birth in relationship to the winter virus peak. Infant birth approximately 4 months before the winter virus peak carried the highest risk, with a 29% increase in odds of developing asthma compared with birth 12 months before the peak (adjusted odds ratio, 1.29; 95% confidence interval, 1.19-1.40). Infant age at the winter virus peak was comparable to or greater than other known risk factors for asthma.
  
  
  CONCLUSIONS
  Timing of birth in relationship to winter virus season confers a differential and definable risk of developing early childhood asthma, establishing winter virus seasonality as a causal factor in asthma development. Delay of exposure or prevention of winter viral infection during early infancy could prevent asthma.
authors.affiliation: Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8300, USA.
authors.forename: Pingsheng
authors.initials: P
authors.lastname: Wu
authors.forename: William D
authors.initials: WD
authors.lastname: Dupont
authors.forename: Marie R
authors.initials: MR
authors.lastname: Griffin
authors.forename: Kecia N
authors.initials: KN
authors.lastname: Carroll
authors.forename: Edward F
authors.initials: EF
authors.lastname: Mitchel
authors.forename: Tebeb
authors.initials: T
authors.lastname: Gebretsadik
authors.forename: Tina V
authors.initials: TV
authors.lastname: Hartert
mesh_terms: D001249:Asthma / Q000209:etiology*; D001990:Bronchiolitis, Viral / Q000150:complications*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D016017:Odds Ratio; D010850:Picornaviridae Infections / Q000150:complications*; D018357:Respiratory Syncytial Virus Infections / Q000150:complications; D012229:Rhinovirus; D012307:Risk Factors; D012621:Seasons
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