title: Trends in the age of diagnosis of childhood asthma.
abstract: BACKGROUND
  The cause of rising asthma incidence over time remains unexplained. Examining trends in the age of diagnosis across successive birth cohorts may offer insights into asthma etiology.
  
  
  OBJECTIVE
  To examine trends in the age at asthma diagnosis and the age and proportion of children hospitalized at first asthma diagnosis in Ontario, Canada.
  
  
  METHODS
  Eight consecutive birth cohorts of children (1993-2000) were observed using administrative data from a universal health insurance plan in Ontario, Canada (population 13 million). Trends in the need for hospitalization and age at asthma diagnosis were examined with descriptive and survival analyses.
  
  
  RESULTS
  The records of 1,059,511 children were examined, of whom 201,958 developed asthma in the first 8 years of life, with an average cumulative incidence of 19.1%. Mean age at asthma diagnosis decreased from 4.7 ± 1.5 years in birth year 1993 to 2.6 ± 2.0 years in birth year 2000 (P < .0001), with a higher adjusted risk of asthma diagnosis (hazard ratio, 6.7; 95% CI, 6.5-6.9) in the first 3 years of life for children born after 1996 versus children born in the period 1993 to 1995 (hazard ratio, 1.4; 95% CI, 1.3-1.4). The proportion of children hospitalized at asthma diagnosis stayed stable while the age at first asthma hospitalization decreased over time (P < .0001).
  
  
  CONCLUSIONS
  This study demonstrates a significant increase in asthma incidence and a decrease in the age of asthma diagnosis across multiple birth cohorts. Changes in asthma incidence over time are primarily explained by variations in asthma rates in children younger than 3 years.
authors.affiliation: Children's Hospital, London Health Sciences Centre, London, Ontario, Canada; Department of Pediatrics, Western University, London, Ontario, Canada; Institute for Clinical Evaluative Sciences, London, Ontario, Canada. Electronic address: dhenuka@gmail.com.
authors.forename: Dhenuka Kannan
authors.initials: DK
authors.lastname: Radhakrishnan
authors.affiliation: Division of Respiratory Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Sharon D
authors.initials: SD
authors.lastname: Dell
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada; Division of Pediatric Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
authors.forename: Astrid
authors.initials: A
authors.lastname: Guttmann
authors.affiliation: Institute for Clinical Evaluative Sciences, London, Ontario, Canada.
authors.forename: Salimah Z
authors.initials: SZ
authors.lastname: Shariff
authors.affiliation: Institute for Clinical Evaluative Sciences, London, Ontario, Canada.
authors.forename: Kuan
authors.initials: K
authors.lastname: Liu
authors.affiliation: Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada; Child Health Evaluative Sciences, Hospital for Sick Children, Toronto, Ontario, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Teresa
authors.initials: T
authors.lastname: To
mesh_terms: D017668:Age of Onset; D001249:Asthma / Q000175:diagnosis* / Q000453:epidemiology* / Q000628:therapy; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009864:Ontario / Q000453:epidemiology; D012189:Retrospective Studies
keywords: Asthma; administrative data; child; epidemiology; incidence; prevalence; rate