Occupational asthma is caused by an immune reaction to specific agents that are inhaled in the workplace. There are around 400 causative agents, although a small number of these cause most cases. It is different from work-aggravated asthma.
Frequently affected professions include:
- Bakers/pastry makers
- Animal workers (including in the laboratory)
- Detergent powder manufacturers
- Fish and seafood processors
- Other food processing workers
- Paint sprayers
- Foam manufacturers
- Electronic solderers
Rhinitis is always a feature, usually preceding chest symptoms. Asthma symptoms start mild, then worsen.
Occupational rhinitis and asthma typically start between 6 and 18 months after the first exposure or change in exposure. This latency period is one of the things that make the diagnosis difficult. However, it is important to make the diagnosis early as removing the trigger can improve or eliminate symptoms, and delay in doing so makes it more likely that the patient will be left with persistent asthma symptoms, with fixed airflow obstruction in a worst-case scenario.
Making the diagnosis
In all patients with new-onset rhinitis, wheeze, or airflow obstruction symptoms, ask whether they’re better on days away from work and during holidays. If either is the case, consider referral to a specialist occupational respiratory unit (unfortunately, the article didn’t list where these are, which wasn’t very helpful).
Initial investigation is with serial peak flows measured at least four times daily (preferably 2 – 3-hourly) for at least three weeks, covering days at work and days away. This investigation has a sensitivity of around 80% and a specificity of around 90%. Interpretation of the results is best done by specialists, but it can be initiated in primary care pending an appointment. Further investigation, in secondary care, may include skin prick tests/specific IgE assays.
Management is with avoidance of further exposure to the causative antigen. In many cases, this may be possible to achieve without changing jobs, by use of substitution of the agent in question, redeployment of the employee to another area, and/or use of respiratory protective equipment. About 25% of employees can continue working in their current job.
People with occupational asthma are eligible to claim industrial injuries disabilities benefit in the UK.
Source: BMJ article ‘Occupational asthma’, BMJ 2016;353:i2658, plus SIGN guidelines referenced in article.