The incidence of work-related asthma-like symptoms and dust exposure in Norwegian smelters

Rationale: The prevalence of respiratory symptoms amongemployees 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 ¼ 2,476) was 8,469 years, and the median follow-up time for participantswas 4.0 years.During the follow-up, 91employees 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 ofWASTH increased significantly (P ¼ 0.0001)with dust exposure in the middle andhighcategories (1.0–2.9 and>3.0mg/m3). Stratifiedanalyses showedthat theeffect ofcurrent dust exposure varied with both previous exposure (PE) to dust and fumes (P ¼ 0.006) and airflow limitation (AFL) (P ¼ 0.033). The final analyses showedthat the risk ratios forWASTHper 1mg/m3...