title: Prolonged episodes of persistent asthma: A distinct clinical pattern with characteristic clinical features.
abstract: OBJECTIVE
  To investigate a clinical pattern of unexplained persistent asthma that is episodic in nature and lasts for months to years. This pattern of prolonged episodes of unexplained, persistent asthma was not defined previously.
  
  
  METHODS
  Investigating the clinical features using a retrospective cohort design.
  
  
  METHODS
  Eighteen subjects (ages, 13 to 64 years) from an allergy practice in a large prepaid health maintenance organization who had two or more prolonged episodes of unexplained persistent asthma lasting >/= 2 months during a 12-year period.
  
  
  RESULTS
  These subjects accounted for 39 asthmatic episodes lasting from 2 to 74 months (median, 7 months). The duration of the episodes positively correlates with the severity of asthma (p = 0.02) at the initial part of the episodes. All episodes demonstrated a similar pattern, with symptom severity greatest at the onset and gradually diminishing until recovery. The relatively symptom-free intervals between the episodes ranged from 1.5 to 63 months (median, 13 months). Fifty-six percent of the episodes (95% confidence interval [CI], 40% to 72%) were associated with symptoms very suggestive or suggestive of an infection of the upper respiratory tract at the onset of the episodes; 33% of the episodes (95% CI, 19% to 50%) had possible symptoms suggestive of an infection; whereas only 10% of the episodes (95% CI, 3% to 24%) had questionable or no symptoms suggestive of an infection of the upper respiratory tract. Thirty-four episodes had the onset between September and March, whereas only 5 episodes occurred between April and August (p < 0. 001).
  
  
  CONCLUSIONS
  These observations indicate that prolonged episodes of unexplained, persistent asthma lasting for months to years constitute a distinct clinical pattern of asthma with characteristic clinical features.
authors.affiliation: Department of Allergy and Immunology, Kaiser Permanente Northwest Region, Portland, OR 97227, USA. kuo.chang@kp.org
authors.forename: K C
authors.initials: KC
authors.lastname: Chang
authors.forename: W M
authors.initials: WM
authors.lastname: Vollmer
authors.forename: M J
authors.initials: MJ
authors.lastname: Barrett
authors.forename: R
authors.initials: R
authors.lastname: Lawrence
authors.forename: K M
authors.initials: KM
authors.lastname: Ettinger
authors.forename: J M
authors.initials: JM
authors.lastname: Carney
authors.forename: F F
authors.initials: FF
authors.lastname: Gill
mesh_terms: D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D002908:Chronic Disease; D015331:Cohort Studies; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000150:complications / Q000175:diagnosis; D008297:Male; D008875:Middle Aged; D012129:Respiratory Function Tests; D012141:Respiratory Tract Infections / Q000150:complications* / Q000175:diagnosis; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D012720:Severity of Illness Index