The Incidence of Work-related Asthma-like Symptoms and Dust Exposure in Norwegian Smelters

Rationale: The prevalence of respiratory symptoms among employees in smelters is positively associated with dust exposure. Objectives: To investigate the association between the incidence of work-related asthma-like symptoms (WASTH) and dust exposure. Methods: All the employees were invited to participate in a 5-year longitudinal study. The outcome of WASTH was defined as the combination of dyspnea and wheezing improving on rest days or vacation in an individual who had no asthma previously. Information about smoking and occupational status was obtained from a questionnaire. A job exposure matrix of total dust was developed. Multivariate data analyses were performed using Cox regression. Measurements and Main Results: The total follow-up time of the employees (n = 2,476) was 8,469 years, and the median follow-up time for participants was 4.0 years. During the follow-up, 91 employees developed WASTH, and the corresponding incidence rate for WASTH per 1,000 person-years was 8.9 (7.3-10.9) (95% confidence interval in parentheses). The risk ratio of WASTH increased significantly (P = 0.0001) with dust exposure in the middle and high categories (1.0-2.9 and >= 3.0 mg/m(3)). Stratified analyses showed that the effect of current dust exposure varied with both previous exposure (PE) to dust and fumes (P = 0.006) and airflow limitation (AFL) (P = 0.033). The final analyses showed that the risk ratios for WASTH per 1 mg/m(3) increase in current dust exposure were 1.1 (0.93-1.2), 1.4 (1.1-1.8), 1.6 (1.1-2.3), and 1.9 (1.2-3.0) for the categories (PE+/AFL-), (PE-/AFL-), (PE+/AFL+, and (PE-/AFL+). Conclusions: In conclusion, dust exposure was associated with an increased incidence of WASTH.