Epidemiology and risk factors of occupational repiratory asthma and occupational sensitization.

Information on the occurrence of occupational asthma comes from different sources; disease registries, general population studies and workforce-based studies. Each source has its strengths and weaknesses. For multi-causal diseases such as asthma, reliable information from wel-designed epidemiological studies is to be preferred. However, a complication is that occupational asthma is not directly measured (diagnosed) in general population studies and an attributable risk is usually calculated on the basis of crude information about exposure. The exposure information is usually derived from questionnaire responses to questions on exposure to gases, fumes or dusts, or is based on so-called 'job exposure matrices'. Disease registry data, from occupational disease registries, allows direct estimation of the occurrence of the occupational asthma. However, the information is often incomplete or difficult to interpret because of diagnostic criteria which vary and can also be dependent on compensation and insurance criteria, more related to severity of disease rather than to occurence of disease. As a result, registries may give only crude estimates of the occurence of diesase, but at the same time allow evalution of trends over time. Workforce-based studies have given most information about determinants of work-related asthma and allergy. An important determinant of asthma and allergy is the exposure intensity and for high-molecular-weight sensitizers atopy clearly modifies the risk. It is expected that improved phenotypical characterization of occupational asthma together with genotyping and detailed exposure assessment will give more insight in the occurence and determinants of disease and prognosis.