Monday, December 12, 2005

Asbestos x-ray findings increase with latency

Am J Ind Med. 1994 May;25(5):635-48.

The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group.

Welch LS, Michaels D, Zoloth SR.

George Washington School of Medicine, Washington, D.C.

This report presents data gathered from a series of asbestos disease screening examinations of 9,605 United States sheet metal workers who were first employed in the trade at least 20 years before the examination. The overall prevalence of asbestos-related radiographic changes was 31.1%: 18.8% had pleural abnormalities alone, 6.6% had parenchymal abnormalities (International Labour Office (ILO) score of 1/0 or higher) alone, and 5.7% had both. Among those with 40 years or more since entering the trade, 41.5% had radiographic signs of asbestos-related disease, 24.2% pleural alone, 7.7% parenchymal alone, and 9.6% both pleural and parenchymal abnormalities. After controlling for several surrogates for asbestos exposure level, cigarette smoking was found to increase risk of parenchymal, and more modestly, pleural abnormalities. Each pack-year was associated with a 1% increased prevalence odds ratios for parenchymal abnormalities (ILO category 1 compared to category 0), and 0.4% increased prevalence odds ratios for pleural abnormalities. A history of shipyard employment also produced significantly increased prevalence odds ratios for each radiographic category. More that 90% of chest radiographs were classified by A or B readers; after adjustment for other risk factors, A readers were more likely to report parenchymal abnormalities of category 1, but not more likely to report category 2 or pleural abnormalities, than B readers.

BrooklynDodger comments: This abstract came up as the Dodger was thinking about a reheating of asbestos compensation legislation.

A notable feature of union based asbestos screening programs was involvement of quality occupational health scientists who could put the results into the peer reviewed literature. These results provide real useful data for public health purposes.

A key dispute is whether a lung cancer victim with asbestos exposure gets compensated in the absence of x-ray evidence of asbestos effect. This paper sheds important light on the importance of latency in observing x-ray evidence of asbestos effect. The Dodger doesn't have access to the full text of the paper, so these comments are based on the abstract. To get into the study, you needed 20 years of latency, years since hired. Overall, there were 31% with x-ray abnormalities, but with 40 years latency there were 41%, suggesting a near doubling in rate from 20 to 40 years. The appearance of x-ray findings appears a combination of ripening of scarring from past exposure with increasing scarring from more exposure with longer duration.

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