Re: "Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry"

Our plain-English summary of Re: "Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry", by G.W. Gibbs (American Journal of Epidemiology, 1998).

The study

• Author: G.W. Gibbs
• Journal: American Journal of Epidemiology
• Published: 1998;148(3):307; author reply 308-9
• Type of article: Comment, Letter
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

In this letter, the author commented on an updated mortality study of diatomaceous earth workers by Checkoway et al. (Am J Epidemiol 1997). He argued that misclassification of asbestos exposure and asbestos-silica interactions may have influenced its results and interpretation. An earlier reanalysis had excluded workers employed before 1930, because asbestos was definitely used in the facility then but specific jobs and exposure levels could not be identified. The update included these workers and extrapolated 1930 job-specific estimates to earlier years. The author stated that no asbestos was used in the facility in 1930 and that asbestos exposure was assigned only to maintenance workers. As a result, pre-1930 production workers were treated as nonexposed, although some may have had high asbestos exposure, which carries its own lung cancer risk. He noted that the only non-asbestos-exposed group with a rate ratio above 1.00 was the highest silica category (13 deaths, rate ratio 2.03). He asked how much of this excess was due to the five lung cancer deaths among pre-1930 hires. Citing the reanalysis, he reported standardized mortality ratios from 1.34 in non-asbestos-exposed silica workers to 4.4 (CI 1.20-11.3) with more than 6.8 fibers/ml-years of asbestos, and 8.32 (CI 1.71-24.3) for the highest asbestos and silica category. He concluded that the update's asbestos categories (>0-1.2 and >1.2 fibers/ml-years) may have diluted effects at higher asbestos levels and influenced the conclusion of no asbestos effect.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This is a letter to the editor, not a new study. The author commented on a 1997 update by Checkoway et al. of deaths among diatomaceous earth workers, arguing that asbestos exposure misclassification and asbestos-silica interactions may have influenced it. The author stated that no asbestos was used in the facility in 1930 and that asbestos exposure was assigned only to maintenance workers. As a result, production workers hired before 1930 were treated as unexposed, although some may have had high asbestos exposure. The author noted that in that paper, the only workers without asbestos exposure whose lung cancer rate ratio exceeded 1.00 were in the highest silica category (13 deaths, rate ratio 2.03), and that five lung cancer deaths occurred among pre-1930 hires. The author cited an earlier 1996 reanalysis, also by Checkoway et al., in which standardized mortality ratios reached 8.32 (CI 1.71-24.3) for the highest asbestos and silica category. The author argued that the update's asbestos categories may have diluted effects at higher concentrations and influenced its conclusion of no asbestos effect.

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: Letter to the editor commenting on a published cohort mortality study (Checkoway et al. 1997); not original research
• Who was studied: No population was studied by the author. The letter discusses the diatomaceous earth worker cohort analysed by Checkoway et al. The author's reference list names the Manville diatomaceous earth plant, Lompoc, California.
• Exposure: Crystalline silica and asbestos (fiber type not specified) in the diatomaceous earth industry, with asbestos measured in fibers/ml-years
• Main results:
  • The author stated that no asbestos was used in the facility in 1930 and that asbestos exposure measures were assigned to maintenance workers only. The source cited for this is a 1994 report by the author and Christensen, prepared for the International Diatomite Producers Association.
  • The author argued that production workers employed before 1930 were treated as unexposed to asbestos, although some may have had high asbestos exposure.
  • The author stated that the earlier reanalysis examined confounding by asbestos only in workers whose main asbestos exposure occurred after 1950, when levels were lower.
  • Citing table 7 of Checkoway et al., the author noted that the only non-asbestos-exposed workers with a lung cancer rate ratio above 1.00 were those in the highest silica exposure category (13 deaths, rate ratio = 2.03). The author also noted that five lung cancer deaths occurred among pre-1930 hires.
  • Citing the 1996 reanalysis, the author listed standardized mortality ratios for silica workers by asbestos exposure: 1.34 with no asbestos exposure, 1.15 for 0 to less than 2.7 fibers/ml-years, and 1.99 for 2.7 to less than 6.8 fibers/ml-years.
  • In the same cited reanalysis, the standardized mortality ratio was 4.4 (CI 1.20-11.3) for workers exposed to silica and more than 6.8 fibers/ml-years of asbestos.
  • In the same cited reanalysis, the standardized mortality ratio was 2.00 (CI 0.73-4.35) for workers with no asbestos exposure and the highest silica exposure.
  • In the same cited reanalysis, the standardized mortality ratio was 8.32 (CI 1.71-24.3) for the highest category of exposure to both asbestos and silica.
  • The author noted that the 1997 update used asbestos exposure categories of more than 0 to 1.2 and more than 1.2 fibers/ml-years.
• The authors' conclusion: The author concluded that the update's choice of asbestos exposure categories may have diluted effects at higher asbestos concentrations and influenced its conclusion that asbestos had no effect.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Dose-response relationship, Lung Cancer, Asbestos Exposure, rate ratio, standardized mortality ratio (SMR).

Related studies

• Re: "Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry" — M.J. Mirliss (1998)
• Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry — H. Checkoway, N.J. Heyer, et al. (1997)
• Extended follow-up of lung cancer and non-malignant respiratory disease mortality among California diatomaceous earth workers — L.G. Gallagher, R.M. Park, et al. (2015)
• Reanalysis of mortality from lung cancer among diatomaceous earth industry workers, with consideration of potential confounding by asbestos exposure — H. Checkoway, N.J. Heyer, et al. (1996)
• Mortality from non-malignant respiratory disease in the fibreglass manufacturing industry — L. Chiazze, D.K. Watkins, et al. (2002)
• Radiographic evidence of silicosis risk in the diatomaceous earth industry — J.M. Hughes, H. Weill, et al. (1998)

Browse more research in American Journal of Epidemiology, or return to medical research.