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Online Depository
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Factors Influencing Duration of Exposure with Symptoms
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and Direct Costs of Occupational Asthma
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David Miedinger, M.D., Jean-Luc Malo, M.D., Herberto Ghezzo, Ph.D.
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Jocelyne L’Archevêque, R.T., Maria-Victoria Zunzunegui, Ph.D.
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Methods
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This is a cross-sectional study investigating subjects who claimed compensation for
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occupational asthma (OA) at the Workers’ Compensation Board of Quebec
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(Commission de la santé et sécurité du travail du Québec; CSST) between the years
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2004 to 2006. Subjects were exposure-free from the offending allergens causing OA
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for two years or more and were evaluated by two of the four Quebec CSST medical
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committees in Montreal (Montreal Chest Institute and Hôpital du Sacré-Coeur) for
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permanent disability indemnity. In Québec, all subjects who claim compensation for
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OA undergo specific inhalation testing for evaluation. All claimants scheduled for
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evaluation by the committees were asked to participate in this study on a voluntary
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basis. We added questions regarding current employment status, participation in past
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rehabilitation programs and other socioeconomic factors as well as validated
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psychological and quality-of-life questionnaires to in our investigation. Subjects were
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assured that the medical committee would not be informed of their acceptance or
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refusal to participate in this study nor of the results of these tests. Subjects were
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granted compensation to cover expenses like loss of salary and transportation and/or
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parking fees. All study subjects gave written consent for their participation. The
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research protocol was approved by the Research Ethics Committee of our hospital.
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The data is reported in accordance with STROBE guidelines[1].
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All subjects answered a questionnaire on chest and upper airway symptoms,
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medication use, home allergen exposure and tobacco consumption. Furthermore,
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subjects were asked to fill out a questionnaire about the type of agent causing the
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occupational asthma and if in fact, they were still being exposed to it. A questionnaire
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about socioeconomic outcomes like current employment, salary, schooling, country
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of origin, number of dependent children and family members relying on the
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household income, information about the Workers’ Compensation Board’s Social
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Rehabilitation Program (job education, full or partial participation in the Job Education
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Program, use of the employment agency) and the WCB records were consulted to
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obtain information concerning costs for compensation for loss of income and
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compensation for functional impairment.
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The number of years of exposure in the workplace with symptoms before
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removal from exposure (YWS) was determined by consulting the Workers’
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Compensation Board file. We recorded the time period as noted by the local medical
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committee in the initial official report. The cut-off values for low income have been
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issued by Statistics Canada and take into account the individual’s place of residency
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and the number of dependent family members[2]. We defined low income as having
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an income at diagnosis that was less than 110% of the cut-off value for low income
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according to the definition laid out by Statistics Canada.
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All subjects underwent spirometry according to ATS guidelines before and
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after receiving bronchodilator medication to determine forced expiratory volume for
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one second (FEV1) and forced vital capacity (FVC)[3]. Reference values for FEV1
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and forced vital capacity (FVC) were calculated according to the formulas derived by
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Knudson and co-workers[4]. Methacholine challenge tests were performed according
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to a previously published protocol[5]. In brief, subjects inhaled methacholine in
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increasing concentrations using a Wright’s nebuliser (output=0.14 mL*min -1; Aerosol
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Medical Ltd., Colchester, UK) with a maximum concentration of 32mg*mL -1. The test
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was ended when a significant fall of FEV1 greater or equal to 20% compared to the
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baseline measurement occurred. Normal responsiveness was set at a provocative
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concentration of methacholine causing a 20% fall (PC20) in FEV1 of greater than 16
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mg*mL-1[6]. Changes in PC20 were considered significant when there was a 3.2-fold
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or greater difference from the value obtained at the time of diagnosis[7].
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Skin prick tests were performed to assess atopic status according to the
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method described by Pepys[8]. For sputum induction, subjects inhaled increasing
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concentrations (3%, 4%, and 5%) of hypertonic saline and the samples were
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processed according to a previously published protocol[9, 10].
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The asthma severity at diagnosis, at re-evaluation and the proportion of
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permanent disability that was allocated were calculated according to the Quebec
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Workers’ Compensation Board Scale for OA: 0% low severity, 100% Maximum
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severity)[11]. This scale incorporates three factors in the same way as the one
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proposed by the American Medical Association[12]: level of bronchial calibre, degree
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of bronchial responsiveness and need for medication to control asthma [13]. We
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estimated the change in asthma severity by substracting the score at re-evaluation
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from that at diagnosis. For some analysis we dichotomized the data by using a cut-off
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of 18%. This severity reflects mild obstruction (FEV1%predicted 71-85%), mild
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bronchial hyperresponsiveness (PC20 2-16 mg*mL-1) and regular of if needed
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bronchodilatator use.
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We consulted the participant’s file at the Québec Workers’ Compensation
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Board to determine the compensation costs for OA. The compensation for loss of
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income and compensation for functional impairment as well as total costs are
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reported in this study. Compensation for loss of income corresponds mainly to
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compensation for lost salary during the rehabilitation period (up to two years) after a
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worker is removed from the workplace harbouring the offending work agent.
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Compensation for functional impairment is allocated at the time of re-evaluation by
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the orkers’ Compensation Board, i.e., about two years after diagnosis and after
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subsequent removal from the workplace and is calculated according to the orkers’
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Compensation Board Scale for OA.
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Results
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Change of objective measurements between diagnosis and re-evaluation
There was no significant change in spirometric results between diagnosis and
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re-evaluation. 50 subjects (83%) underwent methacholine challenge testing at
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diagnosis and at re-evaluation. The proportion of subjects with hyperresponsiveness
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(PC20≤16mg/ml) decreased significantly (at diagnosis 57 (98%) vs. 36 (69%),
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p<0.001). When considering the change in airway responsiveness, 35 (70%) had an
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increase of ≥2-fold, 10 (20) a increase <2-fold and 5 (10) a decrease in PC20. Thirty-
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four subjects (57%) were able to produce interpretable induced sputum
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measurement at diagnosis and 46 (77%) at re-evaluation. Eosinophil, neutrophil and
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total cell count did not change significantly between diagnosis and re-evaluation.
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The proportion of those receiving no treatment for asthma, being on treatment with
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only a short-acting bronchodilator, being on inhaled steroids and the dose of inhaled
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steroids administered did not change significantly between diagnosis and re-
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evaluation. There was an increase in the proportion of subjects inhaling long-acting
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bronchodilators (12 (20%) at diagnosis vs. 25 (42%) at re-evaluation, p=0.004). The
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distribution of subjects according to smoking status remained unchanged, but one
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smoker had stopped smoking and one former smoker had resumed smoking.
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Overall, the amount of improvement in asthma severity in this cohort was only
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moderate (improvement 3.1% mean ±14.3%, 5% median (Q1;Q3:-2.0%;9.5%).
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Sixteen subjects (27%) saw a worsening of their asthma, in 29 subjects (48%)
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asthma severity remained unchanged or the improvement was less than 9% and 15
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subjects (25%) experienced an improvement of 10% or more at re-evaluation.
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We classified subjects according to the results of the methacholine challenge
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test at re-evaluation as either hyperreactive or normoreactive. Those classified as
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hyperreactive had a significantly higher hyperreactivity to methacholine at diagnosis,
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a higher asthma severity score at re-evaluation (16% (Q1;Q3: 13%;28%) vs. 11%
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(Q1;Q3: 8%;20%), p=0.041), longer exposure in the workplace with symptoms before
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removal from exposure (2.6 years (Q1;Q3: 0.5 years;7.8 years) vs. 0.6 (Q1;Q3: 0.1
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years;1.3 years), p=0.040) and were more often from a higher income bracket than
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CAD 30,000.— (25 (78%) vs. 7 (22%), p= 0.050).
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References
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