US prevalence of occupational pleural thickening. A look at chest X-rays from the first National Health and Nutrition Examination Survey.

The prevalence of occupational pleural thickening in the United States in the mid-1970s was estimated; since asbestos often produces pleural thickening, this estimate in turn was used to estimate the prevalence of asbestos exposure. Chest x-rays obtained by the 1971-1975 National Health and Nutrition Examination Survey were reread by three readers using the International Labour Office criteria for diagnosis of pleural thickening consistent with dust exposure. All 289 x-rays showing any pleural abnormalities plus a 3-to-1 age-, sex-, and race-matched control series were reread. Using two of three readings as "positive," and extrapolating to the US population from this defined sample, the authors showed that 2.3% of males and 0.2% of females had occupational pleural thickening on x-ray, with a strong increase with age in white males. This provides a US population estimate of 1.3 million people with occupational pleural thickening and approximately 8 million people with asbestos exposure in the mid-1970s. This cohort might make a substantial contribution to cancer mortality into the next century.