Controversies in epidemiology of occupational asthma.

Epidemiology is the study of the distribution, determinants and outcome of disease. In this article, the recently acquired knowledge of the epidemiology of occupational asthma is described, as well as current areas of controversy. Incidence figures obtained from field studies in high-risk workplaces, medicolegal statistics and sentinel programmes indicate that approximately 10% of adult-onset asthma is attributable to the workplace. The strategy to identify cases through questionnaires and tools that address functional, immunological and physiopathological issues needs to be improved. Although few in number and limited to a handful of workplaces, cohort studies found that the risk of developing occupational asthma is determined less by individual susceptibility (e.g. atopy, tobacco smoking, human leukocyte antigen phenotype) and more by the level of exposure to its causes; in general, the higher the exposure, the greater the risk, and, by implication, lowering the level of exposure reduces the incidence of disease. Occupational asthma can be used as a satisfactory model for the development of adult-onset asthma. There is a great need to develop intervention strategies through adequate surveillance programmes in high-risk workplaces.