RADIOGRAPHIC ABNORMALITIES AND MORTALITY IN SUBJECTS WITH EXPOSURE TOCROCIDOLITE

Plain chest radiographs from a one in six random sample of the workfor ce of the asbestos industry at Wittenoom, Western Australia between 19 43 and 1966 have been classified for degree of profusion and pleural t hickening by two independent observers according to the 1980 UICC-ILO Classification of Radiographs for the pneumoconioses to clarify the ef fect of degree of radiological abnormality on survival. A total of 110 6 subjects were selected. Each subject's age, cumulative exposure to c rocidolite, and time since first exposure were determined from employm ent records, the results of a survey of airborne concentrations of fib res >5 mu in length conducted in 1966, and an exposure rating by an in dustrial hygienist and an ex-manager of the mine and mill at Wittenoom . By the end of 1986 193 subjects had died. Conditional logistic regre ssion was used to model the relative risk of death in five separate ca se-control analyses in which the outcomes were deaths from: (1) all ca uses, (2) malignant mesothelioma, (3) lung cancer, (4) asbestosis, and (5) other causes excluding cancer and asbestosis. Up to 20 controls p er case were randomly chosen from all men of the same age who were not known to have died before the date of death of the index case. After adjustment for exposure and time since first exposure, there were sign ificant and independent effects of radiographic profusion and pleural thickening on all cause mortality. The effect of profusion was largely a result of the effect on mortality from malignant mesothelioma and a sbestosis but not lung cancer. The effect of pleural thickening was gr eatest on mortality from other causes, mainly ischaemic heart disease. This study has shown that degree of radiographic abnormality has an i ndependent effect on mortality from malignant mesothelioma, asbestosis , and all causes even after allowing for the effects of age, degree of exposure, and time since first exposure.