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 [...]