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

Our plain-English summary of US prevalence of occupational pleural thickening. A look at chest X-rays from the first National Health and Nutrition Examination Survey, by W.J. Rogan, B.C. Gladen, N.B. Ragan, et al (American Journal of Epidemiology, 1987).

The study

• Authors: W.J. Rogan, B.C. Gladen, N.B. Ragan, H.A. Anderson
• Journal: American Journal of Epidemiology
• Published: 1987;126(5):893-900
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000347).

Abstract

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.

In plain English

The authors estimated how common occupational pleural thickening was in the United States in the mid-1970s, and from this how many people had been exposed to asbestos. Three certified readers independently reread chest x-rays from the 1971-1975 first National Health and Nutrition Examination Survey. They reread all 289 x-rays originally reported as showing pleural abnormalities and a matched series, three times as large, reported as showing none. An x-ray counted as positive if at least two readers agreed. Of 1,103 usable x-rays, 59 were positive. Weighted to the US population aged 25-74, estimated rates were 2.31 per cent for males, 0.21 per cent for females and 1.21 per cent overall, or about 1.29 million people. Rates in white males rose after age 40. Assuming that all cases came from occupational asbestos exposure, which they said was not exactly correct, and using rates in shipyard workers, the authors approximated about 8 million exposed workers alive then, a figure they expected to be somewhat conservative. The authors considered it reasonable that occupational asbestos exposure accounted for most positive findings. They noted a single x-ray is not the most sensitive tool.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Population prevalence study: chest x-rays from a national health survey were reread by three certified readers using International Labour Office criteria. The survey's sampling weights were then used to project the results to the US population.
• Who was studied: Chest x-rays from the 1971-1975 first National Health and Nutrition Examination Survey, a sample of the civilian, non-institutionalized US population. The 1,156 reread x-rays were 289 originally reported as showing pleural abnormalities and 867 originally reported as not showing pleural abnormalities (a 3-to-1 series matched for race, sex and closest age). Of these, 1,103 were usable. Estimates cover people aged 25-74.
• Exposure: Exposure was not measured directly. Pleural thickening read as consistent with pneumoconiosis was used as a marker of occupational exposure, which the authors attributed largely to asbestos. No fiber types were named.
• Main results:
  • Of the 59 positive x-rays (out of 1,103 usable), 46 were called positive by all three readers.
  • The estimated prevalence of occupational pleural thickening was 0.21 per cent (standard error 0.07) in females and 2.31 per cent (standard error 0.47) in males.
  • The estimated prevalence for the population as a whole was 1.21 per cent (standard error 0.22).
  • Applied to the US population aged 25-74, this gave an estimated 1.29 (standard error 0.24) million people with pleural thickening consistent with asbestos exposure: 1.17 million males and 0.12 million females.
  • Among white males, prevalence increased strongly with age, with rates rising after age 40.
  • The three readers differed in how many x-rays they called positive: 57 of 1,094, 58 of 1,103, and 103 of 1,103.
  • The authors assumed that all cases resulted from occupational asbestos exposure, which they said was not exactly correct. They also took figures from other studies of shipyard workers and assumed one person with x-ray abnormalities represented about six occupationally exposed people. On that basis they approximated about 8 million occupationally exposed workers alive in 1971-1975.
  • Of the 283 usable films that the original reading had shown as having any pleural abnormality, only 50 met the study's criteria.
• The authors' conclusion: The authors considered it reasonable that occupational exposure to asbestos accounted for most of the positive findings. They also said the data show that pleural thickening consistent with asbestos exposure is widespread in the general population.
• Limitations the authors state:
  • Oversampling of strata with original abnormalities left younger ages undersampled. This produced a high but unstable estimate for nonwhite males aged 40-44.
  • Five strata under age 40 were not sampled and were assumed to have zero prevalence. Assuming 5 per cent in each instead raised the overall estimate to 1.39 per cent.
  • There was nonresponse at all levels of the original survey, and its effect on the estimates is difficult to estimate.
  • The originally negative comparison x-rays came from people who had pulmonary function tests. These people tended to be younger and included fewer nonwhites.
  • Readers could not be blinded to age and sex, which raises the possibility of observer bias.
  • The authors could not fully rule out pleural abnormalities due to other causes such as infection or trauma.
  • Readers had only a single film and no history or other data, so some films would have been diagnosed differently with more information.
  • A single posterior-anterior x-ray is not the most sensitive way to detect pleural abnormalities, so true numbers are likely underestimated.
  • The estimate of 8 million exposed workers assumed that all cases resulted from occupational asbestos exposure, which the authors said is not exactly correct. The error introduced by this assumption could not be quantified.
  • The relation of pleural thickening to smoking was not examined.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Thickening, Chest X-Ray, Asbestos Exposure.

Related studies

• Re: "US prevalence of occupational pleural thickening: a look at chest x-rays from the first National Health and Nutrition Examination Survey" — W.C. Cooper (1989)
• Relationship of mortality, occupation, and pulmonary diffusing capacity to pleural thickening in the First National Health and Nutrition Examination Survey — D.P. Loomis, G.W. Collman, et al. (1989)
• X-ray evidence of increased asbestos exposure in the US population from NHANES I and NHANES II, 1973-1978. National Health Examination Survey — W.J. Rogan, N.B. Ragan, et al. (2000)
• Assessment of physicians' proficiency in reading chest radiographs for pneumoconiosis, based on a 60-film examination set with two factors constituting eight indices — T. Tamura, Y. Kusaka, et al. (2018)
• A survey of pleural thickening: its relation to asbestos exposure and previous pleural disease — (1972)
• The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group — L.S. Welch, D. Michaels, et al. (1994)

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