Pre-employment assessment and health surveillance for employees exposed to occupational asthmagens: overview

The recent publication of an evidence-based review of occupational asthma [1] has highlighted the areas for which there is little evidence to guide the practising occupational physician dealing with workers exposed to occupational asthmagens. In particular, there is little or no evidence for effective management of prospective employees with a pre-existing or current history of asthma. There are few studies of efficacy of health surveillance programmes and an absence of guidance regarding important components and recommended frequency of assessment. This in-depth review sets out to review these important practical subjects for occupational physicians and where there is little evidence gives example of good practice from major employers in a number of different industries. The final paper looks to the future and the emerging areas of knowledge. The paper by Tarlo and Liss [2] sets out areas where good evidence exists for prevention of occupational asthma now thought to account for 10% of adult-onset asthma. Early diagnosis and early removal from exposure are essential to minimize the impact of occupational asthma once it has developed. Following diagnosis, the management of choice is complete removal from exposure, but even with early intervention there will be socio-economic consequences. The evidence for health surveillance is less certain, but one of the major studies [3] in Ontario is discussed in detail. Although there was some evidence of benefit, improvements in incidence were temporarily related to other hygiene changes in the workplace, which may have impacted on the development of occupational asthma. Areas which still need to be addressed include the important components and the optimum frequency of health surveillance assessments. In the paper by Linnet [4] the practice of a major platinum refiner is described. Platinum is a potent sensitizer with between 25–90% of employee populations becoming sensitized. Its refining also involves exposure to a number of irritants. The current practice is to exclude smokers and current active asthmatics on treatment. A previous history of asthma would exclude an employee if he/she were young and had not been tested in an industrial environment. Skin-prick testing with platinum salts is the mainstay of health surveillance and is conducted on a 3-monthly basis in areas of high exposure. The platinum industry does not exclude atopics because it is now recognized that exclusion of this group, prevalent in the general population, would exclude a large proportion of potential employees who would never go on to develop occupational asthma. The paper by Gannon [5] describes a global integrated programme for the prevention, early detection and mitigation of occupational asthma in an industry where employees work with isocyanates. The reason isocyanates cannot often be substituted are discussed. The practical issues of a global company policy which has to integrate with local legal and accepted professional practice are described. The authors suggest that this approach could be a model for other industries. The final paper by Malo [6] looks to future advances. What is the significance of repeated exposure to low-level irritants in the development of occupational asthma? What is the prognosis of pre-existing asthma made worse by exposures in the workplace? What is the mechanism of asthma for the low-molecular-weight asthmagens? Topics such as the protective effect of endotoxins, diagnostic abilities of induced sputum examination and treatment with inhaled corticosteroids are also discussed. Another area of interest is why some employees recover after removal from exposure and others do not. Not all aspects of occupational asthma relevant to the practising occupational physician are known, nor will they be because of problems of ethics, practicality and ability to control real working populations in an experimental fashion. Where this evidence is unavailable then examples of good practice from a range of industries should help to inform our daily work in this area. Ultimately type and frequency of surveillance will be governed by sensitizing agent, level of exposure and local statutory legislation.

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