Modelling prevalence and incidence of fibrosis and pleural plaques in asbestos-exposed populations for screening and follow-up: a cross-sectional study

Our plain-English summary of Modelling prevalence and incidence of fibrosis and pleural plaques in asbestos-exposed populations for screening and follow-up: a cross-sectional study, by C. Paris, A. Martin, M. Letourneux, et al (Environmental Health, 2008).

The study

• Authors: C. Paris, A. Martin, M. Letourneux, P. Wild
• Journal: Environmental Health
• Published: 2008;7:30
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: CT-Scan is currently under assessment for the screening of asbestos-related diseases. However, to date no consensus exists as to how to select high-risk asbestos-exposed populations suitable for such screening programs. The objective of this study is to select the most relevant exposure variables for the prediction of pleural plaques and asbestosis in order to guide clinicians in their use of CT-Scan.

Methods: A screening program of non malignant asbestos-related diseases by CT-scan was conducted among asbestos-exposed volunteers in France. Precise assessments of asbestos exposure were obtained by occupational hygiene measurements and a job-exposure matrix. Several parameters were calculated (time since first exposure, duration, intensity and cumulative exposure to asbestos). Predictive parameters of prevalence and incidence were then estimated by standard logistic and a complementary log-log regression models.

Results: 1011 subjects were recruited in this screening program among them 474 (46.9%) presented with pleural plaques and 61 (6.0%) with interstitial changes compatible with asbestosis on CT-scan. Time since first exposure (p < 0.0001) and either cumulative or mean exposure (p < 0.0001) showed independent associations with both pleural plaques and asbestosis prevalence and pleural plaques incidence. Modelling incidence of pleural plaques showed a 0.8% to 2.4% yearly increase for a mean exposure of 1 f/ml.

Conclusion: Our findings confirmed the role played by time since first exposure and dose but not duration in asbestos-related diseases. We recommend to include these parameters in high-risk populations suitable for screening of these diseases. Short-periodicity of survey of pleural plaques by CT-Scan seemed not to be warranted.

In plain English

This French study analysed 1,011 asbestos-exposed volunteers, mainly from asbestos textile, friction materials, insulation and energy production plants, screened by CT scan in a Normandy program begun in 1991. CT scans showed pleural plaques in 474 people (46.9%) and interstitial changes compatible with asbestosis in 61 (6.0%). The odds of having pleural plaques rose with time since first exposure (odds ratio 1.075 per year, 95% confidence interval 1.059 to 1.092) and with average exposure level (1.114 per fibre/ml, 95% CI 1.077 to 1.153). Duration of exposure did not predict plaques after adjusting for time since first exposure. For asbestosis, the best-fitting model included age and average exposure. Modelling estimated that yearly plaque incidence rose from 0.8% at 10 years to 2.4% at 30 years after first exposure, for an average exposure of 1 fibre/ml. The authors concluded that time since first exposure and dose, but not duration, should be included in high-risk definitions for screening. They also concluded that short-interval CT follow-up for plaques seemed not warranted. They noted the volunteers were not representative of the general population.

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: Cross-sectional study of participants in a CT-scan screening program. Prevalence was modelled with logistic regression, and incidence was inferred with complementary log-log regression.
• Who was studied: 1011 asbestos-exposed volunteers (over 50 years, including retirees) in a screening program begun in 1991 in Normandy, France. They came from plants with past heavy asbestos use: mainly asbestos textile and friction materials fabrication, insulation and energy production.
• Exposure: Occupational asbestos exposure; fiber types not specified. Exposure was estimated from a job-exposure matrix built on airborne measurements (1959 to 1999) in an asbestos textile and friction material plant, or from published measurements in the French Evalutil database. The exposure descriptors analysed were:
• time since first exposure
• duration of exposure
• cumulative exposure index (fibers/ml.years)
• mean exposure (cumulative exposure divided by duration)
• Main results:
  • Among the 1011 subjects screened by CT-scan, 474 (46.9%) had pleural plaques and 61 (6.0%) had interstitial changes compatible with asbestosis.
  • Pleural plaque prevalence, time since first exposure: odds ratio per year 1.075 (95% CI 1.059, 1.092) in Model 1 and 1.067 (95% CI 1.051, 1.083) in Model 2.
  • Pleural plaque prevalence, mean exposure (Model 1): odds ratio per fibre/ml 1.114 (95% CI 1.077, 1.153).
  • Duration of exposure was not a significant predictor of pleural plaque prevalence after adjusting for time since first exposure.
  • In the incidence model with mean exposure, yearly pleural plaque incidence increased from 0.8% 10 years after onset of exposure to 2.4% 30 years after onset, for a mean exposure of 1 fibre/ml.
  • In the pleural plaque incidence model, the relative risk for a 10 f/ml mean exposure compared with a 2 f/ml mean exposure was 1.74.
  • The shortest observed latency for a subject with pleural plaques was 16 years.
  • For asbestosis prevalence, time since first exposure and cumulative exposure were statistically significant together. However, the best-fitting model included age and mean exposure, with odds ratio 1.09 per f/ml (95% CI 1.04, 1.14) for mean exposure.
  • No estimate could be obtained for the incidence of asbestosis.
  • Based on the incidence model, the authors suggested a CT-scan follow-up interval for pleural plaques of 5 to 10 years.
• The authors' conclusion: The authors concluded that their findings confirmed the role of time since first exposure and dose, but not duration, in asbestos-related diseases. They recommended including these parameters when defining high-risk populations for screening. They also concluded that short intervals between CT scans for pleural plaques seemed not warranted.
• Limitations the authors state:
  • The population was not representative of the general population, as only asbestos-exposed volunteers were included.
  • Participation rates were not assessed for all plants, so no analyses by industrial sector were done.
  • Only presumably healthy subjects were enrolled. The most severe asbestosis cases were likely diagnosed beforehand and excluded, which, with the small number of cases, may explain the difficulty modelling asbestosis incidence.
  • The incidence model assumes that inclusion did not depend on disease status. The authors said this is likely not a problem for pleural plaques but is one for asbestosis.
  • Atmospheric exposure measurements like those used in this study are rarely available, which limits how clinicians can apply the results.

Topics

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

Medical terms in this study, explained in our Lexicon: Fibrosis, Pleural Plaques, Asbestos Exposure, Cumulative Exposure, Interstitial.

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