Abstract
RATIONALE: Severe asthma is a public health problem with limited information regarding preventable causes. Although occupational exposures have been implicated as important risk factors for asthma and asthma exacerbations, associations between occupational exposures and asthma severity have not been reported. OBJECTIVE: To examine associations between occupational exposures and asthma severity. METHODS: The Epidemiological Study on the Genetics and Environment of Asthma combines a case-control study with a family study of relatives of patients with asthma. Adult patients (n = 148) were recruited in chest clinics and control subjects without asthma (n = 228) were population-based. Occupational exposures to nonasthmogenic irritants and asthmogens (classified as "any asthmogen" including three broad groups: high-molecular-weight agents, low-molecular-weight agents, and mixed environments) were assessed by an asthma-specific job exposure matrix. Asthma severity was defined from an 8-grade clinical score (frequency of attacks, persistent symptoms, and hospitalization). Patients with severe (score >or= 2) and mild asthma were compared with control subjects using nominal logistic regression. MAIN RESULTS: Significant associations were observed between severe adult-onset asthma and exposure to any occupational asthmogen (odds ratio [OR], 4.0; 95% confidence interval [CI], 2.0-8.1), high-molecular-weight agents (OR, 3.7; CI, 1.3-11.1), low-molecular-weight agents (OR, 4.4; CI, 1.9-10.1), including industrial cleaning agents (OR, 7.2; CI, 1.3-39.9), and mixed environments (OR, 7.5; CI, 2.4-23.5). No significant associations were found between nonasthmogenic irritants and asthma severity, nor between asthmogens and childhood-onset asthma or mild adult-onset asthma. CONCLUSIONS: Our results suggested a strong deleterious role of occupational asthmogens in severe asthma. Clinicians should consider occupational exposures in patients with moderate to severe asthma.