Prevalence and incidence of benign asbestos pleural effusion in a working population

Our plain-English summary of Prevalence and incidence of benign asbestos pleural effusion in a working population, by G.R. Epler, T.C. McLoud, E.A. Gaensler (JAMA, 1982).

The study

• Authors: G.R. Epler, T.C. McLoud, E.A. Gaensler
• Journal: JAMA
• Published: 1982;247(5):617-22
• Cited by: 157 articles, as counted by NIH iCite
• Read it: PubMed
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000668).

Abstract

Benign asbestos effusion was defined by (1) exposure to asbestos, (2) confirmation by roentgenograms or thoracenteses, (3) no other disease related to pleural effusion, and (4) no malignant tumor within three years. There were 34 benign effusions among 1,135 exposed workers compared with no otherwise unexplained effusions among 717 control subjects. Prevalence was dose related with 7.0%, 3.7%, and 0.2% effusions with severe (III), indirect (II), and peripheral (I) exposure, respectively. The latency period was shorter than for other asbestos-related disorders. Benign effusion was the most common asbestos-related abnormality during the first 20 years after exposure. Incidence studies showed 9.2 effusions per 1,000 person-years for level III exposure, 3.9 for level II, and 0.7 for level I. Most effusions were small; 28.6% recurred, and 66% were asymptomatic. There was one mesothelioma six years after effusion. Asbestos exposure should be carefully searched for in patients with "idiopathic" pleural effusion.

In plain English

The authors studied how often benign (non-cancerous) pleural effusion, fluid around the lungs, occurred in asbestos-exposed workers. They reviewed serial chest X-rays and medical records of 1,135 employees, including 45 women, from six workplaces (shipyards, a fireproofing product plant and specialty paper mills). They compared them with 717 male university employees. Workers were grouped by peripheral (level I), indirect (level II) or direct (level III) exposure. The authors counted 35 benign asbestos effusions among exposed workers (3.1%) and no otherwise unexplained effusions among controls. Prevalence was 7.0%, 3.7% and 0.2% at levels III, II and I. The yearly rate was about nine per 1,000 workers at level III, four at level II and fewer than one at level I. In workers with level II or III exposure, effusion was the most common asbestos-related abnormality in the first 20 years after exposure. Most effusions were small, two thirds reported no symptoms, and ten workers (28.6%) had recurrences. One person developed mesothelioma six years after the effusion. The authors said 3.1% was probably an underestimate, and that follow-up was too short to measure later mesothelioma.

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: Survey of serial chest roentgenograms and medical records of asbestos-industry employees compared with a control group (cross-sectional prevalence plus incidence over person-years of observation)
• Who was studied: Survey group: 1,135 employees, including 45 women, from six plants (two shipyards, a fireproofing product manufacturer, and three specialty paper mills), seen at industrial sites. Control group: 717 male university employees whose X-rays were available on a recall list. Initial X-rays dated back to 1935 for asbestos workers and to 1940 for the university group.
• Exposure: Asbestos exposure in shipyard, fireproofing and paper-mill work. One paper mill included employees heavily exposed to crocidolite while making filter paper during a special project between 1952 and 1956. Employees were assigned to level I (peripheral, such as administrators, clerks, secretaries), level II (indirect, such as certain electricians, welders, mechanics, shipfitters, machine operators) or level III (direct, such as pipecoverers, asbestos mixers, sweepers).
• Main results:
  • Pleural effusions of all kinds were five times more common in the survey group (4.8%) than in control subjects (1.0%), P<.001.
  • The survey group had 35 workers with benign asbestos effusion, a prevalence of 3.1%. The control group had no otherwise unexplained effusions.
  • Prevalence of asbestos effusion in the survey group was 7.0% at exposure level III, 3.7% at level II and 0.2% at level I.
  • By job, asbestos effusions were most common among asbestos pipecoverers (7.3%).
  • Annual occurrence was about nine asbestos effusions per 1,000 employees exposed at level III, four at level II, and fewer than one per 1,000 at level I.
  • The latency analysis included only persons exposed at level II or III, because only for them was onset of exposure precisely known. In this group, benign asbestos effusion was the most common asbestos-related abnormality during the first 20 years after exposure. No asbestosis, pleural plaques or calcifications were seen in the first ten years after initial exposure.
  • The latent period was shorter for the 23 level III workers (13.3 years) than for the 11 level II workers (15.2 years), but this difference was not statistically significant.
  • Most effusions were small. Two thirds of the workers reported no symptoms during their effusion. Recurrent effusions developed in ten persons (28.6%).
  • Of the 35 workers with asbestos effusion, 54% had residual diffuse pleural thickening.
  • Mean follow-up after the first effusion was 9.7 years. In the survey group, one person was found to have a mesothelioma six years after the initial benign effusion. Three persons in the survey group died: two from asbestosis and one from that mesothelioma.
• The authors' conclusion: The authors concluded that a 3.1% prevalence of benign effusions in the asbestos exposed should alert physicians to this disorder when diagnosing 'idiopathic' (unexplained) pleural effusion.
• Limitations the authors state:
  • The 3.1% prevalence was probably an underestimate. First X-rays were sometimes taken many years after initial exposure, lateral or oblique films were often missing, and some effusions may have cleared without trace between films.
  • Control subjects had fewer X-rays, usually every third year, so effusions in the control group could also have been underestimated.
  • Some of the 35 effusions may have had other causes than asbestos.
  • The university environment of the control group differed from that of large shipyards or factories.
  • Some control subjects had previous asbestos exposure. 13 controls (1.8%) had typical pleural plaques.
  • Follow-up was not long enough to determine the incidence of mesothelioma after asbestos effusion.

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: Benign Asbestos Pleural Effusion, Pleural Effusion, Latency, Mesothelioma, Asbestos Exposure, Idiopathic.

Related studies

• Symptomatic benign pleural effusions among asbestos insulation workers: residual radiographic abnormalities — R. Lilis, Y. Lerman, et al. (1988)
• Retrospective investigation on diagnostic process for benign asbestos pleural effusion (BAPE) using checklist — T. Kishimoto, N. Fujimoto, et al. (2020)
• Benign asbestos pleural effusion associated with pulmonary aspergilloma — J. Hiyama, M. Marukawa, et al. (1998)
• Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners — W.O. Cookson, N.H. De Klerk, et al. (1985)
• MicroRNA and mRNA features of malignant pleural mesothelioma and benign asbestos-related pleural effusion — G. Ak, S.C. Tomaszek, et al. (2015)
• Benign asbestos pleural effusion: diagnosis and course — B.W. Robinson, A.W. Musk (1981)

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