UNUSUAL PULMONARY OBSERVATIONS AND EXPOSURE TO COALMINE DUST: A CASE-CONTROL STUDY

Abstract

A study of five doctors' classifications of 4330 miners' serial chest radiographs identified 45 cases of unusually rapid development of simple pneumoconiosis (the criterion being that at least three of the doctors judged that the increase in profusion of small rounded opacities during approx. 10-yr intervals between films amounted to two or more steps of change on the 12-point simple pneumoconiosis scale). Forty-one matched controls were selected from the same nine collieries using analogous criteria to determine the absence of any increase in the profusion of small rounded opacities. The cases had worked 926 more hours on average during the 10 yr than the controls, and their mean exposures to respirable mixed coalmine dust were also slightly higher, by 0.2 mgm'3. However, the only statistically significant differences between cases and controls in the environmental variables considered were for indices reflecting exposures to quartz in the mixed dust. The highest standardized mean difference referred to the percentages of quartz in the exposures which were 6% on average for the cases and 5% for the controls. The median quartz level in the 10-yr exposures of all 4330 men studies was 4.6%. Average rates of decline in lung function over the 10-yr intervals did not differ significantly. Smoking and breathlessness were both slightly more prevalent among the cases, but a standardized measure of timed Forced Expiratory Volume at the earlier radiological surveys was better for the cases. Progressive Massive Fibrosis (PMF) was seen on the later films from 10 cases and three controls. Attacks or progression of PMF were recorded for nine cases and one control. The disproportionately high number of attacks or progression of massive fibrosis among the cases is statistically significant at the 5% level. It is concluded that unusually rapid progression of simple pneumoconiosis accompanied by the occurrence of massive fibrosis is associated with relatively high percentages of quartz in exposures to mixed coalmine dust, but it is clear that exposure to quartz is not the sole factor responsible for the development of PMF.