Occupational asthma: causes, symptoms, diagnosis and treatment

By Cristiano Antonino On Apr 11, 2023

Occupational asthma is a disease characterised by diffuse, intermittent and reversible airway obstruction caused by a specific allergen present in the work environment

Occupational asthma is different from bronchoconstriction in a person with idiopathic asthma exposed to an irritant

Many irritants encountered in the work environment can exacerbate idiopathic asthma, but such reactions do not constitute occupational asthma.

Occupational asthma usually begins after an exposure of at least 18 months to 5 years; it does not occur before one month of activity unless sensitisation has occurred previously.

Once sensitised to a specific allergen, a person invariably responds to much lower concentrations of allergen than those that normally elicit a response (measured in ppm or ppb).

Occupational asthma affects only a minority of workers.

Causes of occupational asthma

Occupational allergens include castor beans, cereal seeds, proteolytic enzymes used in detergent production and in the brewing and leather industries, western red cedar wood, isocyanates, formalin (rarely), antibiotics (e.g. ampicillin and spiramycin), epoxy resins and tea.

The list is constantly growing.

Although it is tempting to attribute most forms of asthma to a type I (IgE-mediated) or a type III (IgG-mediated) immunological response, such a simplistic approach is not justified.

Reactions may vary and bronchospasm may occur shortly after exposure or later, e.g. up to 24 h later with nocturnal recurrence for a week or more without further exposure.

Symptoms and signs of occupational asthma

Patients typically complain of wheezing, chest tightness, wheezing and coughing, often with upper respiratory tract symptoms such as sneezing, rhinorrhoea and lacrimation.

Symptoms may occur during working hours after exposure to dust or specific vapours, but often occur several hours after work stops, making the association with occupational exposure less obvious.

Night-time wheezing may be the only symptom. Symptomatology often disappears at weekends or during holidays.

Diagnosis

Diagnosis is based on recognition of exposure to the aetiological agent in the working environment and immunological tests (e.g. skin tests) conducted with the suspected antigen.

An increase in bronchial hyperreactivity after exposure to the suspected antigen also helps in making the diagnosis.

In more difficult cases, a positive inhalation provocation test, performed in the laboratory and carefully controlled, confirms the cause of airway obstruction.

Pulmonary function tests, which show a reduction in ventilatory capacity during work, are further confirmation that occupational exposure plays a causal role.

The differential diagnosis with idiopathic asthma is generally based on the symptom picture and the relationship to allergen exposure.

Therapy

Treatment of bronchial asthma (usually involving an oral or aerosol bronchodilator, theophylline and, in severe cases, corticosteroids) improves symptoms.

Prophylaxis

In industries where allergenic or bronchoconstrictive substances have been identified, the elimination of dust is essential; however, the elimination of all opportunities for sensitisation and clinical disease is not feasible.

If possible, a particularly sensitive individual should be removed from the environment that causes him or her asthmatic symptoms. If exposure continues, symptoms tend to persist.