title: The course of asthma activity: a population study.
abstract: BACKGROUND
  Unlike most chronic diseases, which tend to progress over time, asthma is known to persist, possibly resolve, and/or present with any combination of remissions and relapses. As a result, its course has been difficult to characterize and its prognosis difficult to predict.
  
  
  OBJECTIVE
  To quantify the proportion of individuals with asthma who have active disease and, of those, the proportion who experience significant gaps in their asthma activity; and to determine factors associated with asthma activity.
  
  
  METHODS
  Universal population health administrative databases were used to identify all individuals with asthma living in Ontario, Canada, in 1993 and follow them for 15 years. Active asthma was indicated by 1 or more physician claims for asthma.
  
  
  RESULTS
  Of 613,394 individuals with asthma in 1993, 504,851 (82.3%) had active disease in subsequent years. Of those who had complete follow-up, 74.6% experienced a gap of 2 or more years in their asthma activity. Previous asthma claims, older and younger age, and a codiagnosis of chronic obstructive pulmonary disease correlated with greater asthma activity.
  
  
  CONCLUSIONS
  Over 15 years, most individuals with asthma in Ontario, Canada, had active disease that was interspersed by periods of inactivity when they did not require medical attention and were likely in remission. These analyses offer insight into the natural course of asthma activity that may help improve the ability to predict an individual's course of disease.
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada. andrea.gershon@ices.on.ca
authors.forename: Andrea
authors.initials: A
authors.lastname: Gershon
authors.forename: Jun
authors.initials: J
authors.lastname: Guan
authors.forename: J Charles
authors.initials: JC
authors.lastname: Victor
authors.forename: Chengning
authors.initials: C
authors.lastname: Wang
authors.forename: Teresa
authors.initials: T
authors.lastname: To
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology* / Q000503:physiopathology; D002170:Canada; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007345:Insurance Claim Review; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology* / Q000503:physiopathology; D012008:Recurrence; D012189:Retrospective Studies; D012307:Risk Factors; D012959:Socioeconomic Factors; D013997:Time Factors; D055815:Young Adult