Objectives: There is little information on the changes in the pattern of occupational asthma (OA) over time. The objective of this study was to evaluate the time trends in the incidence and causes of immunological OA in Belgium using workers' compensation data.
Methods: Cases of OA were identified through a retrospective review of all claims submitted by salaried workers to the Belgian Workers' Compensation Board from 1993 to 2002. The likelihood of OA was categorized as definite, probable, or possible based upon the results of from diagnostic procedures. Time trends were evaluated using Spearman's rank correlation for crude numbers of cases and through the negative binomial regression for incidence rates of OA per industry.
Results: From a total of 1852 claims, 971 were categorized as having definite, probable, or possible OA. There was a downward trend in the annual number of cases due to the main causes of OA (i.e. flour, isocyanates, woods, and enzymes) and an apparent increase in cases of latex-induced OA. The estimated average annual incidence of OA was 29.4 (95% CI: 27.6-31.3) new cases per million salaried workers during the 1993-2002 period. There was a significant decline in the overall incidence rate of OA throughout the study period from 35.5 new cases per million salaried workers in 1993 to 25.8 in 2002.
Conclusions: These compensation-based data indicate that there has been a global downward trend in the incidence of OA during the nineties, although the factors that determined this reduced incidence should be further investigated.
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