Occupational Asthma

 

• Background

  Asthma due to an occupational exposure.

  Causes

  • High molecular mass substances: flour, wood dust, lab animal allergens. May have specific, detectable IgE.
  • Low molecular mass substances – e.g. isocyanates (furniture foam, paint spray), welding fumes, oil mists – which act as haptens and bind to human proteins. Often hard to detect specific IgE.

  Epidemiology

  • 15% of asthma, though only identified as such in 2%.
  • Commonest cause of new-onset occupational respiratory disease. Commoner than 'occupational lung diseases' i.e. occupational pneumoconiosis or hypersensitivity pneumonitis.
  • But remember that, even in adults, only a minority of new asthma is occupational.

• Presentation

  • Typical asthmatic/hypersensitivity symptoms: cough, SOB, wheeze, rhinitis, conjunctivitis.
  • Onset within 1 year of starting job.
  • Initial latent interval without symptoms – weeks to months – while hypersensitivity develops.
  • Symptoms may occur at work, or hours post-exposure in the evening or night, reflecting a delayed response.
  • Symptoms worsen throughout week, but improve at weekends and holidays.

• Risk factors

  • Work involving exposure to known causes, especially if in high volume.
  • Atopy
  • FH of atopy or asthma.
  • Smoking
  • Pre-existing asthma.

• Investigations

  • Serial peak flow is the best way to determine a relationship, know as a 'workplace challenge'. May involve repeated measurements over 24 hours or a week.
  • Skin prick testing or allergen-specific serum IgE. Not available for most causes.
  • Inhalation challenge (aka bronchial provocation) test of possible cause in lab. Rarely done due to potential risks.

• Management

  Change or stop work:

  • If work stopped within 2 years of symptoms onset, it usually improves.
  • If stopped after 2 years, it often persists.
  • Eligible for Industrial Injury Benefit if symptoms continue post-work.

  Employer responsibilities for employee safety:

  • Must inform HSE of any death, injury causing 3 days off, near misses, or occurrence of a reportable disease. Several respiratory conditions are reportable, including occupational asthma, hypersensitivity pneumonitis, and pneumoconiosis.
  • 1st line response should be removing the causative agent, or failing that, reducing exposure.