Severity of pulmonary asbestosis as classified by International Labour Organisation profusion of irregular opacities in 8749 asbestos-exposed American workers. Those who never smoked compared with those who ever smoked.

The profusion of irregular opacities on chest roentgenograms by International Labour Organisation pneumoconiosis criteria was used to assess the severity of asbestosis in 8749 asbestos-exposed active and retired American workers. Seventy-eight percent had no asbestosis (category 0/0 or 0/1), 18.6% had slight asbestosis (1/0 to 1/2), 3% had moderate asbestosis (2/1 to 2/3), and 0.3% had advanced disease (3/2 or greater). Significantly more current smokers had asbestosis than did those who had never smoked, and their average profusion of opacities was higher. The mean age of current smokers with asbestosis was 60 years, whereas subjects with the disease who had never smoked had a mean age of 64 years, a significant difference. Cigarette smoking and asbestosis appear to act synergistically to produce irregular opacities on chest roentgenograms of asbestos-exposed American workers.