SeriesOccupational asthma
Section snippets
Causative agents
About 250 agents capable of causing occupational asthma have been reported.6 Some of the more common agents are shown in the panel. They can be classified into three groups according to the possible pathogenetic mechanisms. In many instances, several mechanisms may be involved.
Pathological changes
Whatever the nature of the agent and its pathogenetic mechanism, the resultant changes in the airways are inflammation with airway hyperresponsiveness. Bronchial biopsy samples from patients with occupational asthma caused by compounds of high and low molecular weight show similar changes, with denudation of airway epithelium, subepithelial fibrosis, and infiltration of the mucosa with inflammatory cells—similar to the changes found in patients with non-occupational asthma.8 Immunostaining
Clinical features
The clinical picture of occupational asthma depends on the agents and the pathogenetic mechanism involved. Occupational asthma mediated through immunological mechanisms is characterised by a latency period between first exposure and onset of symptoms; only a proportion of exposed workers develop asthma; and re-exposure to very low concentrations of the causative agent provokes symptoms. Inhalation challenge tests with agents that produce specific IgE antibodies commonly provoke an isolated
Epidemiology
Occupational asthma is common. The frequency may be very high in some industrial settings. For example, an early study in the platinum-refining industry suggested that 46% of workers had occupational asthma.12 30 years later, about 25% of a cohort of platinum-refinery workers developed occupational asthma during 4 years of follow-up, most within the first year.13 In other industries, only sporadic cases may be reported, but an apparently isolated case may be the first sign of a much more
Natural history
The risk of occupational asthma appears to be highest soon after first exposure, but the latent interval can vary from months to years.27 Occupational asthma is a potentially fatal condition. Necropsy information on a patient with occupational asthma caused by an isocyanate has been reported.28 A fatal case of asthma in a baker has been reported.29
Withdrawal from exposure may or may not lead to improvement in asthma or bronchial hyper-responsiveness.27 The total duration of exposure, the
Diagnosis
The diagnosis of occupational asthma should be considered in every case of adult-onset asthma or worsening asthma in adult life. In immunologically mediated asthma, the characteristic symptoms are of asthma that improves during weekends and holidays. Improvement may take several days, and the patients feel best in the second week of a 2-week holiday or on Monday morning after Saturday and Sunday off work. Nocturnal or early-morning asthma may occur after a shift working with the causal agent.
Management
Avoidance of exposure is the mainstay of patient management. Ideally, patients should withdraw from the causal exposure permanently, retraining if necessary for alternative employment. In practice, patients may reject this advice for economic reasons. Larger companies may be able to relocate the patient to reduce exposure and provide respiratory protection. If there is a possibility of low or occasional exposure, the patient should remain under medical supervision and peak-flow records and
Impairment/disability assessment
Patients with asthma are characterised by variable airflow obstruction and airway hyperresponsiveness. They have to avoid exposure to dust, gases, and fumes, and they may be at a disadvantage in their future employment. The results of their lung function tests may be normal with the use of drugs. The guidelines for assessment of impairment and disability for patients with chronic irreversible disease are inappropriate for patients with asthma. The guidelines recommended by the American Thoracic
Prevention
Primary prevention includes elimination of the agent from the workplace by substitution or process change. Reduction of exposure can also be achieved through isolation, enclosure, and improved local exhaust. Good housekeeping, maintenance, waste disposal, and sanitation practice are important. Exclusion of susceptible individuals from high-risk workplaces after preemployment examination is another method. However, very little is known about host susceptibility factors, with the exception of
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