A 24 year cohort study of mortality in slate workers in North Wales

Aim To study mortality in slate workers in North Wales. Methods A cohort study, with a contemporaneous control group (quasi-experimental study) with follow-up from 1975 to 1998. The date and cause of death in those who had died were identified from the Office of National Statistics. Results Seven hundred twenty six slate workers and 529 age matched controls took part in the survey. We found a clear excess of death rate among slate workers compared with controls, having adjusted for age and smoking habit. This was largely restricted to those ages less than 75. Hazard ratio for all deaths was 1.24 [95% Confidence Interval (CI)=1.04-1.47, P=0.015]. The excess was mainly due to respiratory disease and pneumoconiosis. The hazard ratio for respiratory deaths was 1.85 (95% CI=1.21-2.82). Conclusion It is likely that the excess deaths in the exposed group was due to exposure to slate dust. The accuracy of pneumoconiosis as a cause of death is questionable, but we lack radiographs close to death to confirm it.