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Occupational Asthma   Back to Occupational Health Theme page

2. Nice to Know:

Occupational Asthma (OA) is the most common occupational lung disease in Canada.  It refers to asthma caused by exposure to an agent found in the workplace.

Investigating and Diagnosing Occupational Asthma

Investigation of OA is a stepwise procedure that usually requires early referral to a specialist.  It includes a combination of tests for each patient that are most likely to lead to a definitive diagnosis.  The steps are:

  1. Suspect OA when adult-onset asthma is seen among patients who work
  2. Take history
    • Ask about improvement on weekends or during holidays
    • Explore exposure history
    • Review data sheets on material safety
  3. Confirm asthma
    • Take history and perform physical examination
    • Assess spirometry before and after bronchodilator use
    • Determine airway responsiveness by histamine or methacholine challenge
  4. If history suggests possible sensitizer-induced OA, assess the likelihood of exposure at work
    • Perform serial peak flow or spirometry monitoring during working weeks and during 2 to 4 weeks off work
    • Perform methacholine or histamine challenges at end of work week and after several weeks off work
    • Offer skin tests with workplace allergen if possible and specific laboratory exposure challenge

Management of OA

Based on all the above, the guidelines suggest the following management of occupational asthma:

  1. Treat the asthma
    • Control non-occupational triggers
    • Test asthma medications
    • Offer patient education
  2. Assess work exposure
    • For sensitizer-induced OA, avoid any further exposure by workplace modifications or moving patient
    • If avoidance is impossible, then reduce exposure as much as possible
    • For irritant-induced OA, protect against further high-level exposure
  3. Assist patient in relevant compensation claim and in rehabilitation
  4. Consider co-workers; notify public health and company
  5. Monitor patient’s course objectively