Stydying of Occupational Asthma and Work-Exacerbated Asthma

The Research Ethics Board, the University Health Network, and the University of Toronto provided study approval. Patients with suspected WRA from a occupational lung disease clinic of a teaching hospital, with clinical visits from 2002 to 2004, and additional Ontario WSIB claimants from the same time period completed a questionnaire, which was slightly modified from that used in our pilot study. The questionnaire included age, education level, self-perception of work conditions, and physician factors related to diagnosis. It was administered during the study period by a research assistant to those attending the clinic, just before a clinic visit, and by telephone for the additional WSIB claimants. File extraction included dates and outcomes of physician visits, diagnostic investigations, and exposure agents.


The term sensitizer-induced OA refers to asthma that started during the patient’s working life, with symptoms improving on weekends or holidays off work, pulmonary function evidence of asthma (ie, at least 12% postbronchodilator improvement in FEV1, or a provocative concentration of methacholine causing a 20% fall in FEV1 < 8 mg/mL), and exposure to a known or presumed work sensitizer. Subcategories included the following: definite OA, including at least one positive work-related test result, work-related changes on serial peak flow readings, at least a threefold improvement in the provocative concentration of methacholine causing a 20% fall in FEV1 during a period away from work vs during a work period, a positive skin test response to a relevant sensitizer or positive specific challenge response to a workplace sensitizer, and the absence of conflicting findings; probable OA, including a positive work-related test result but also negative response to another test (eg, positive serial peak flow findings but no significant improvement in methacholine response); and possible OA, a negative result for one objective work-related test, but other tests were not performed or had not been performed by the time of the review.


The term WEA refers to physician-diagnosed asthma, in which symptoms are worse at work, and in which there is workplace exposure to respiratory irritants such as dusts, smoke, fumes, or sprays (Inhalers are the most common method of asthma treatment. To know more you may here Excluded from analyses were the following: unrelated asthma (ie, two or more work-related test results were negative); and irritant-induced asthma (based on criteria reported by Brooks et al or modified).

Statistical Analysis

The outcomes of the analyses (ie, diagnostic milestones) were the time from the onset of work-attributed asthma symptoms to the time of (1) the first physician visit (for OA and WEA), (2) the first physician suspicion of WRA (for OA and WEA), and (3) the final diagnosis (for OA). Personal and workplace variables were examined as possible predictors of outcomes.

Asthma is most common occupational lung disease:

Data analysis was performed using a statistical software package (SAS, version 9; SAS Institute; Cary, NC). Comparisons between OA and WEA groups for the demographic characteristics, individual and workplace factors, and diagnostic tests were assessed using the t test and the x2 test, or, when appropriate, the Wilcoxon test and the Fisher exact test. In univariate analyses, relationships between each response variable and each explanatory variable were examined with the x2 test for binary variables and with logistic regression analysis for continuous variables. Associations of outcomes with covariates were investigated controlling for age and gender. Since the distributions of the time period durations were skewed, we dichotomized them at the median and considered which predictors were associated with a longer duration (greater than median) [additional details are provided in supplemental material on the Web]. Analyses were repeated with subgroups of those patients with probable or definite OA and in WEA subjects who had been assessed by a specialist (results not shown due to similar trends).