Work-related asthma: the occupational question that changes the picture

An adult patient whose asthma will not settle is a familiar problem in general practice. The usual checks follow: inhaler technique, adherence, triggers at home, perhaps a step up in treatment. One question tends to get less attention than it deserves, and it is a simple one. What do you do for work?

The answer matters more often than many clinicians expect. According to the Australian Asthma Handbook, approximately one in four adults with asthma experience asthma symptoms due to their work. An official statement from the American Thoracic Society and the European Respiratory Society put the occupational population attributable fraction for asthma at 16%.

A 2020 position paper from the Thoracic Society of Australia and New Zealand and the National Asthma Council Australia describes work-related asthma as under-recognised and under-reported. It cites estimates of roughly 1,000 to 3,000 new cases of asthma caused by work in Australia each year.

Two conditions under one label

Work-related asthma covers two situations. Occupational asthma is new-onset asthma, or a recurrence after a period of remission, caused by irritants or sensitisers in the workplace. Work-exacerbated asthma is existing asthma that worsens because of airborne triggers at work.

The handbook says sensitisers cause an estimated 90% of occupational asthma, and the TSANZ and NAC paper notes a latency of days to years before symptoms appear. A patient with sensitiser-induced occupational asthma needs early and complete avoidance of the agent. The paper also says workers with work-exacerbated asthma may be able to stay in their job if exposure is controlled.

Who is exposed

The 2014 Australian Workplace Exposure Study estimated that 47% of men and 40% of women were exposed to at least one asthmagen at work, about 2.8 million men and 1.7 million women. The most common exposures were bioaerosols (29%) and metals (27%) among men, and latex (25%) and industrial cleaning and sterilising agents (20%) among women.

More than 300 workplace agents have been described as causes of occupational asthma, but some jobs come up again and again. The TSANZ and NAC paper links isocyanates to spray painters, adhesive workers, polyurethane foam manufacturers, insulation workers and the automotive industry. It links grains and flour to farmers, bakers and millers, wood dust to carpenters, sawmill workers, arborists and sanders, and latex to healthcare workers.

Cleaning products tend to surprise people. The paper notes growing recognition of asthma linked to cleaning agents and disinfectants, naming formaldehyde, glutaraldehyde, hypochlorite bleach, hydrogen peroxide and enzymatic cleaners. That puts cleaners and hospital staff in the frame, not only people in heavy industry.

What to ask

The TSANZ and NAC paper suggests asking whether symptoms differ during weekends or holidays as a useful initial screening question. A patient whose chest is better by Sunday and worse again by Tuesday has handed the clinician a lead worth following. The paper also notes that this pattern fades as asthma becomes more prolonged or severe, so a patient with longstanding disease may not describe it.

From there, the detail matters. The paper recommends asking about the work schedule, tasks, exposures and control measures, including respiratory protection and ventilation. Patients can ask their employer for safety data sheets, although these may not identify a substance’s potential to cause asthma.

The paper adds that work should be considered in every working-age adult with asthma, particularly when asthma starts in adult life or has been difficult to control, and work-related nasal symptoms often come before the asthma, especially with agents such as flour or animal allergens.

Objective testing while the patient is still in the job

The paper says clinical history alone is insufficient for diagnosis. Investigations should start as soon as work-related asthma is suspected, while the worker is still in the role. Relocation during investigation is only necessary if asthma is severe.

Every worker with suspected work-related asthma should have spirometry with bronchodilator reversibility, although normal spirometry does not rule out asthma. Bronchial provocation testing should be done while the patient is still exposed, because airway hyperreactivity can return to normal rapidly once exposure stops.

To link asthma to the workplace, the paper describes serial peak expiratory flow as helpful. It sets out four readings a day (on waking, at noon, at the end of the working day and before bed) for four weeks, including two weeks away from work. Computer analysis with OASYS software has greater specificity than visual inspection (91% vs 69%), according to the paper.

When to refer

The handbook recommends immediate referral to a specialist with expertise in work-related asthma when new-onset symptoms in an adult appear to be triggered by workplace irritants or sensitisers, because the investigation is complex.

The stakes run both ways. The TSANZ and NAC paper notes that missing work-related asthma may worsen asthma control, while an inaccurate diagnosis may lead to unnecessary absence from work and economic hardship. Because leaving a job is likely to carry a significant socio-economic cost, the paper says a specialist should objectively confirm occupational asthma before that decision.

Why speed matters

The handbook states that prompt diagnosis and identification of causal exposures is critical to avoid rapid and potentially irreversible decline in lung function. It also notes that inhaled corticosteroid and long-acting beta agonist treatment has not been shown to prevent long-term worsening in people who remain exposed to the sensitiser.

Removal from exposure is necessary, but it is not a guaranteed cure. A systematic review in Thorax pooled outcomes after avoidance of the causative agent and estimated complete symptomatic recovery at 32%, with persistent bronchial hyperresponsiveness in 73%. Within individual studies, a shorter duration of symptoms was associated with a higher rate of recovery. The authors cautioned that the data were not consistent enough for confident advice to patients. Australian guidance still treats early diagnosis and complete avoidance of the sensitiser as the priority.

The workplace side of the equation

The TSANZ and NAC paper describes a new diagnosis of occupational asthma as a sentinel event. It says the managing clinician has an ethical responsibility to communicate with the workplace, with the patient’s consent, so that co-workers are protected. That can mean reviewing controls and introducing or modifying a health surveillance program for exposed workers, and the paper notes that involving an occupational physician may be warranted. It also recommends early referral to the employer’s workers’ compensation insurer.

The law sets a floor for some exposures. Under the model WHS Regulations, a business must provide health monitoring where a worker’s ongoing work creates a significant risk from a chemical listed in Schedule 14, and isocyanates are on that list. For isocyanates, monitoring covers a demographic, medical and occupational history, a standardised respiratory questionnaire, a physical examination of the respiratory system and skin, and standardised respiratory function tests such as FEV1, FVC and FEV1/FVC. Because the model regulations have no legal effect on their own, the law in force in each state or territory is what applies.

Monitoring must be carried out by or under the supervision of a registered medical practitioner with experience in health monitoring. The report must include any advice that the worker may have developed a work-related disease and any recommendation on whether the worker can continue that work. The business must give the worker a copy, send it to the regulator when it contains either, and keep it confidential for at least 30 years.

Asking the question

An occupational history does not have to be long. The job title, the substances handled and whether symptoms ease away from work will often tell a clinician whether to look further. When the answers point towards the workplace, the next steps are well defined, from serial peak flow while the patient is still working to specialist referral. The hard part is remembering to ask.