Occupational asthma in aluminium potroom workers related to pre-employment eosinophil count

Occupational asthma still occurs in aluminium potroom workers despite pre-employment medical selection. The purpose of our study was to identify workers with an increased risk of developing "potroom asthma". A nested, case-control study was carried out in two Dutch aluminium producing plants. Pre-employment data of 364 potroom workers (182 cases and 182 controls) were analyzed. Cases were workers unable to work because of work-related respiratory disease, meeting the criteria for potroom asthma. The selected controls were matched for age, year of starting employment and working conditions. Pre-employment eosinophil count was significantly related to the occurrence of potroom asthma, even though the mean number of the eosinophils in cases was within the normal range (< 275 cells.mm-3; 0.28 cells x 10(9).L-1). Hence, 39 of the 45 individuals with blood eosinophil counts in the upper range of normal (> 220 cells.mm-3; 0.22 cells x 10(9).L-1) developed potroom asthma with time. We conclude that workers without respiratory symptoms, with normal lung function and normal bronchial responsiveness before employment developed potroom asthma. Fluoride exposure, combined with an elevated eosinophil count, might induce an immunological or cytotoxic process.