The prevalence of asbestos-related lung abnormalities was examined among workers and the spouses of workers formerly employed at a large ceiling tile plant in Minnesota. Between 1958 and 1974, asbestos was utilized in the production of mineral board and ceiling tile. Chest radiographs and other measures of respiratory morbidity were obtained for 995 workers and 444 spouses of workers. Radiographs were evaluated independently by two experienced readers using the 1980 International Labour Organization (ILO) classification of the pneumoconioses. This study also evaluated whether interreader variability in classifying pneumoconioses could be improved through a modification of the ILO protocol.
Screened workers averaged 53 years of age and 26 years latency. The prevalence of parenchymal abnormalities (profusion ${\ge}1/0$) as seen by either reader was 6.4% and was strongly associated with age and marginally with smoking. The prevalence of bilateral pleural changes seen by either reader was 14.2% and was associated with latency, work history, body mass index, and gender. Overall, 28% showed parenchymal profusion ${\ge}1/0$ and/or any pleural changes by at least one reader. This confirms that this cohort had significant exposures to asbestos.
The average age among screened spouses was 55 and the average latency was 28 years. The prevalence of parenchymal profusion ${\ge}1/0$ by at least one reader was 2.3%, while the prevalence of bilateral pleural changes was 0.9%. Overall, the prevalence of parenchymal profusion ${\ge}1/0$ and/or any pleural changes by at least one reader was 5.2%. The low prevalence among spouses and the absence of a control group limit the conclusions that can be drawn from these findings.
Following the ILO classification, readers were shown a brief medical history of the subject and then asked to express the degree of certainty that any radiographic changes were due to a pneumoconiosis. Reader agreement was not improved for either parenchymal or pleural changes by use of this modification. Parenchymal certainty was not associated with smoking nor any other history, while pleural certainty was associated with age, laterality, calcification, plaques, congestive heart failure, and comments on muscle/fat shadows.
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