TABLE 1.

Comparison of how work-exacerbated asthma (WEA) cases were identified in the clinical and epidemiological settings

	Clinical cases	Epidemiological cases
Source of cases	Specialty clinic, with cases referred that had experienced persistent problems with asthma symptoms related to work	Working adults with asthma treated at a health maintenance organization and not necessarily referred for any special evaluation
Criteria for asthma	Symptoms consistent with asthma, and also reversible airflow obstruction or PC20 <8 mg/mL	Diagnosis of asthma in medical records, confirmed by self-report on questionnaire
Criteria for WEA	Worsening of asthma symptoms when exposed at workplace and a negative specific inhalation challenge	Based on self-reported worsening of asthma associated with work and judgement by expert panel that relevant exposures existed at work
Method for ruling out occupational asthma	Could not be WEA if specific inhalation challenge was positive	Asthma cases with onset during time period of interest (past 12 months) were not considered to be at risk for WEA

PC₂₀ Provocative concentration of methacholine causing a 20% fall in forced expiratory volume in 1 s