Abstract

Background
Cobalt has been shown to induce mainly asthma, allergic contact dermatitis and hard metal disease. The data on cobalt asthma are mainly based on case reports.

Aims
To characterize all the cases of occupational cobalt asthma encountered in a cobalt plant at the time of diagnosis and 6 months later. We also evaluated the incidence of cobalt asthma in different departments on the basis of data on occupational exposures.

Methods
We identified cases of cobalt asthma confirmed with specific bronchial challenge tests in the Kokkola cobalt plant in Finland where exposure levels have been regularly monitored.

Results
Between 1967 and 2003, a total of 22 cases of cobalt asthma were diagnosed in the cobalt plant. On challenge tests, mostly late or dual asthmatic reactions were observed. The incidence of cobalt asthma was the highest in the departments with the highest cobalt exposure levels. All cases of cobalt asthma were encountered in departments where irritant gases were present in the ambient air in addition to cobalt. At the time of the follow-up examination 6 months later, non-specific hyperreactivity had mostly remained at the same level or increased.

Conclusions
The incidence of cobalt asthma correlated with the exposure levels of cobalt in corresponding departments. An irritating effect of gaseous compounds may enhance the risk of cobalt asthma and even the smallest amounts of cobalt may be harmful to susceptible workers. Symptoms of asthma may continue despite the fact that occupational exposure to cobalt has ceased.

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