Occupational Medicine Occupational asthma

Occupational asthma may be defined as asthma induced by exposure to an inhaled agent (or agents) in the workplace. Its presentation is sometimes dramatic. Occupational exposure to platinum salts, for example, has been known to induce asthma in over 50% of an exposed workforce. For those affected, the consequences are often devastating, while the economic effects for an industry may be no less profound. Although occupational asthma was barely recognized 30 years ago, its study in recent years has led to much insight into the aetiology and the mechanisms ofasthma in general. A number of comprehensive reviews are available.'`3 It is important to distinguish the induction of asthma from the mere provocation of symptoms in those who are already asthmatic. Any asthmatic worker whose occupation involves moderate exertion might wheeze at work but exercise alone will never induce asthma in the way that chemicals and other occupational agents sometimes do. The concept of airway hyperresponsiveness is useful in understanding this distinction. It refers to the exaggerated responses of the airways to stimuli such as exercise or cold air which are a universal feature of active asthma. If an asthmatic state (airway hyperresponsiveness) has been induced, whether occupationally or not, exposure to these non-specific stimuli gives rise to bronchoconstriction and the symptoms of wheeze, breathlessness and cough. In the case of occupational asthma, there is an additional specific sensitivity to the causative agent in the same way that some, but not all, asthmatics wheeze when exposed to the house dust mite. The quantification of airway responsiveness can be useful in assessing asthmatic activity and in following changes associated with occupational exposures. The overall prevalence ofoccupational asthma is not known with any certainty. Some 3-6% of the adult population in Britain have symptoms of asthma, and of these approximately a third deny being affected in childhood. The prevalence of asthma beginning in adult (working) life is therefore likely to be 1-2% in any workforce but most of these cases will arise coincidentally rather than through a direct effect of occupation. In Japan, it has been estimated that up to 15% of adult onset asthma might have an occupational aetiology, though, for Britain, the figure is considered to be of the order of 2-5%. More accurate information about the epidemiology of occupational asthma in Britain will shortly become available as data from two ongoing investigations are analysed. Under the SWORD (Surveillance of Work-related and Occupational Respiratory Disease) project respiratory and occupational physicians report each month on all new cases of presumed occupational lung disease. In 1989, the first year in which the scheme was operational, asthma proved to be by far the single most commonly reported occupational lung disease. The overall national incidence was of the order of 20 per million employed per year but with very much higher incidences in certain occupations. The second reporting scheme is centred on the West Midlands region and suggests that the local incidence of occupational asthma is appreciably higher.