What is occupational asthma?
Occupational asthma is a type of chronic inflammatory disease of the airways associated with allergens or irritants in the workplace that leads to reduced air flow through the respiratory passages. It is a type of asthma that should be considered in adult asthmatics, especially if the asthma commenced or recurred when working in a specific environment.
Unlike the many other occupational respiratory diseases, like silicosis and asbestosis, some cases of occupational asthma may not have developed entirely in the work environment but exposure to certain irritants or allergens simply caused a recurrence of a pre-existing condition. Discontinuing work or avoiding exposure to trigger factors may allow the condition to resolve spontaneously, without any treatment in some cases, or drastically reduce the severity of the asthma. In chronic cases, particularly severe and poorly controlled cases, there may be lung remodeling with life-long implications.
Pathophysiology of Occupational Asthma
How does occupational asthma occur?
Asthma of any type is a condition associated with significant inflammation of the bronchi and bronchioles – the air tubes that lead to the lungs. This causes the walls of the airways to swell (edema) and there may also be excessive mucus production. Both these processes narrow the bronchial tree. The more pronounced factor, however, is the narrowing caused by contraction of the smooth muscle in the walls of the bronchi. This narrows the lumen even further and may occur in attacks thereby restricting the flow of air significantly.
This inflammation may be due to allergens triggering inflammation due to a hypersensitivity to the particular allergen. Alternatively the inflammation may be a result of irritation by airborne irritants which can irritate any person’s airways but causes a more pronounced effect in some people. The narrowing is often reversible, either partially or completely, with or even without treatment.The characteristic feature in occupational asthma is that the airways are hyper-responsive as with other types of asthma. This means that the response to an allergen or irritant is abnormal and/or unnaturally pronounced. Therefore not every person exposed to these allergens or irritants will develop asthma or experience symptoms.
Types of Occupational Asthma
Occupational asthma can be broadly divided into two categories :
- Hypersensitivity-induced occupational asthma
- Irritant-induced occupational asthma
In the hypersensitivity-induced type of occupational asthma, the patient has an exacerbated immune-mediated reaction which then causes the inflammation. Every time the person is exposed to the allergen, the immune system ‘mistakens’ it for a harmful substance and triggers immune cells and chemical mediators that then promote inflammation. It essentially means that the immune system ‘drives’ the entire inflammatory process in response to allergen exposure in the workplace. A person may have a history of allergies (atopic constitution) with childhood asthma or other atopic conditions like allergic rhinitis or atopic dermatitis (allergy eczema) earlier in life. It can, however, occur in a person with no personal or family history of allergies.
In the irritant-induced type of occupational asthma, exposure to some irritant (usually airborne) inflames the respiratory passages. It may have no association with allergies or a history of atopy and can even be seen in people out of the workplace who live with cigarette smokers or in heavily polluted areas where it is referred to as non-atopic asthma. The airways are still hyperresponsive although the exact reason is uncertain and may affect some people yet not others exposed to the same trigger factors like gases, fumes, organic dusts and chemicals.
Symptoms of Occupational Asthma
The signs and symptoms of occupational asthma are similar to those in other types of asthma. Read more on asthma symptoms. The intensity of the signs and symptoms may vary depending on the severity of the asthma. It is not uncommon for patients to be asymptomatic for long periods while away from work or even for the hours out of the workplace.
Due to medico-legal implications, a diagnosis of occupational asthma has to be carefully made after thorough investigation that clearly establishes a relationship between the onset of signs and symptoms and time in the workplace. It is not uncommon for an asthmatic to experience an exacerbation in the workplace with less severe symptoms out of the workplace. This may not be considered as occupational asthma since it was not induced but simply aggravated by workplace exposure.
Causes of Occupational Asthma
It is difficult to clearly identify causative factors as not all workers are affected by certain allergens and irritants despite longer hours or greater exposure to the same trigger factors seen in those with occupational asthma. While workplace asthma is more frequently seen with certain occupations and the exposure to certain compounds, individual risk factors have to also be taken into account, like cigarette smoking and a history of asthma or atopy.
Allergens and irritants that may cause occupational asthma
- Wood dust
- Animal hair
- Flour and grain dust
- Flux used for soldering and welding
These compounds have been identified as the most common causative factors, of which flour and grain dust and isocyanates account for the higher proportion of occupational asthma.
Types of jobs associated with occupational asthma
- Timber workers
- Paint sprayers
- Bakers and pastry-makers
- Food processing workers
- Chemical workers
- Animal handlers and farmers