Occupational Asthma

Occupational asthma is a respiratory condition characterised by new onset asthma or recurrence of previously quiescent asthma, directly caused by exposure to specific agents in the workplace. It is classified as an occupational lung disease and a type of work-related asthma.

The causative agents can be divided into sensitizers and irritants. Sensitizer-induced asthma is immunologic and occurs after a latency period, while irritant-induced asthma is non-immunologic and occurs due to high dose exposure to irritants.

Signs and Symptoms

Like other forms of asthma, occupational asthma is marked by airway inflammation, reversible airway obstruction, and bronchospasm. Common symptoms include shortness of breath, chest tightness, coughing, sputum production, and wheezing. Upper airway symptoms such as itchy eyes, tearing, sneezing, nasal congestion, and rhinorrhea may also occur. Symptoms can develop over years for sensitizer-induced asthma or rapidly after a single high-concentration exposure in cases like Reactive Airway Dysfunction Syndrome (RADS).

Risk Factors

Over 400 workplace substances have been identified with asthmagenic or allergenic properties. Common agents include flour, diisocyanates, latex, persulfate salts, metals, and wood dusts. The distribution of these agents varies geographically based on industrial activities. For example, bakeries and cake-shops in France, wood dust in Canada, and isocyanates in the automotive industry are notable sources. Occupations at high risk include bakers, millers, animal handlers, healthcare workers, hairdressers, and woodworkers.

Examples of High-Risk Occupations and Agents

• Grains, Flours, Plants, and Gums: Bakers and millers (wheat), farmers (grain dust), tea packers (tea dust).
• Animals, Insects, and Fungi: Bird fanciers (avian proteins), laboratory workers (rats, mice), mushroom cultivators (mushroom spores).
• Chemicals/Materials: Aircraft fitters (triethyltetramine), healthcare workers (glutaraldehyde, latex), hairdressers (persulfate salts).
• Isocyanates and Metals: Car sprayers (hexamethylene diisocyanate), welders (stainless steel fumes), rubber workers (naphthalene diisocyanate).
• Drugs and Enzymes: Pharmaceutical workers (penicillins), detergent manufacturers (Bacillus subtilis), poultry workers (amprolium hydrochloride).
• Woods: Carpenters and timber millers (western red cedar, iroko), wood machinists (kejaat).

Diagnosis

Diagnosing occupational asthma requires confirming asthma symptoms and establishing a causal link to the work environment. Various diagnostic tools are used:

• Spirometry: Measures timed expired and inspired volumes.
• Peak Flow Metre: Measures peak expiratory flow rate (PEFR), comparing values at work and in controlled environments.
• Bronchial Hyperreactivity Test: Involves methacholine or mannitol exposure to assess airway responsiveness through forced expiratory volume (FEV-1).
• Specific Inhalation Challenges: Exposing subjects to suspected agents and monitoring for asthma symptoms and FEV1 reduction.
• Additional Tests: Skin prick tests, serum immunologic testing, and measurement of sputum eosinophils.

Prevention

Preventive measures for occupational asthma include comprehensive programmes, education, training, medical examinations, medications, reducing exposures, and eliminating exposures. Studies indicate that removal or reduction of exposure improves asthma symptoms and lung function, though removal may lead to job loss and decreased income. Early restriction from exposure is advisable to prevent long-term symptoms.

Management

Medication

Medications for occupational asthma are similar to other asthma types, including short-acting beta-agonists (salbutamol, terbutaline), long-acting beta-agonists (salmeterol, formoterol), and inhaled corticosteroids. Immunotherapy may be used for sensitizer-induced asthma cases.

Epidemiology

Occupational asthma is one of the most common occupational lung diseases, accounting for approximately 17% of adult-onset asthma cases. About one-fourth of adults with asthma have work-exacerbated asthma. Those with work-related asthma are more likely to experience severe symptoms and require emergency medical attention compared to other asthma patients.

Society and Culture

Compensation

Diagnosing occupational asthma can lead to significant socio-economic consequences for both workers and employers. Workers may face job loss, unemployment, and compensation issues, while employers deal with hiring and training new personnel. Adhering to safety standards could potentially save costs related to occupational asthma. In the United States, the total cost of occupational asthma in 1996 was estimated at $1.6 billion, highlighting the economic impact of this condition.

---

Self-assessment MCQs (single best answer)

What characterises occupational asthma?

Which of the following is a common symptom of occupational asthma?

Which occupation is at high risk due to exposure to persulfate salts?

What type of test involves exposing subjects to suspected agents to monitor for asthma symptoms and FEV1 reduction?

Which of the following agents is commonly associated with occupational asthma in healthcare workers?

What is a preventive measure for occupational asthma?

Which medication is commonly used to manage occupational asthma?

What percentage of adult-onset asthma cases is attributed to occupational asthma?

Which diagnostic tool measures the peak expiratory flow rate (PEFR)?

What can be a socio-economic consequence of diagnosing occupational asthma?