Routes of asbestos exposure and the development of mesothelioma in an English region

Our plain-English summary of Routes of asbestos exposure and the development of mesothelioma in an English region, by D. Howel, L. Arblaster, L. Swinburne, et al (Occupational and Environmental Medicine, 1997).

The study

• Authors: D. Howel, L. Arblaster, L. Swinburne, M. Schweiger, E. Renvoize, P. Hatton
• Journal: Occupational and Environmental Medicine
• Published: 1997;54(6):403-9
• Cited by: 57 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To investigate the contribution of exposure to asbestos through different routes in the development of mesothelioma.

Methods: Case-control study. 185 confirmed cases of mesothelioma and 160 controls were identified, when death had occurred between 1979 and 1991 in four health districts in Yorkshire. The surviving relatives were interviewed to ascertain lifetime exposure to asbestos. Adjusted odds ratios (ORs) of exposure to asbestos (through occupational, paraoccupational, and residential routes) were calculated for cases and were compared with controls.

Results: Likely or possible occupational exposure to asbestos was more common in cases than in controls (OR 5.6, 95% confidence interval (95% CI) 3.1 to 10.1). After excluding those with likely or possible occupational exposure, likely or possible paraoccupational exposure was more common in cases than controls (OR 5.8, 95% CI 1.8 to 19.2). Only six cases of mesothelioma were identified as being solely exposed to asbestos through their residence, compared with nine controls. The OR for residential exposure to asbestos varied between 1.5 and 6.6, depending on which potential industrial sources were included, but the 95% CIs were so wide that slightly reduced or greatly increased odds comparing cases with controls could not be excluded.

Conclusion: Study results support previous evidence that occupational and paraoccupational exposure to asbestos is associated with developing mesothelioma. Despite a rigorous search, purely residential exposure seemed to account for only 3% of identified cases. No firm conclusion can be drawn about the risks from residential exposure alone, as many of the study subjects could also have been occupationally or paraoccupationally exposed to asbestos.

In plain English

This matched case-control study looked at people who died between 1979 and 1991 in parts of Yorkshire, England. It compared 185 people with confirmed mesothelioma with 159 people who died of other causes, matched by sex, age and year of death. Relatives, or coroners' records for some cases, supplied life histories. These were coded for exposure at work, exposure from household members' asbestos work (called paraoccupational), and living within 0.5 km of factories thought to use asbestos. Likely or possible occupational exposure was found in 150 cases (81%) and 80 controls (50%), an odds ratio of 5.6 (95% CI 3.1 to 10.1). Among people without likely or possible occupational exposure, paraoccupational exposure was more common in cases, but the authors could not say precisely by how much. Only 3% of cases seemed exposed solely through where they lived. Odds ratios for residential exposure ranged from 1.5 to 6.6, with confidence intervals too wide to rule out reduced or greatly increased odds. The authors concluded that this study alone could not show whether residential exposure is a risk factor and that a larger study was needed.

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: Matched case-control study using life histories obtained mainly from interviews with next of kin, analysed with conditional logistic regression
• Who was studied: 185 people with mesothelioma confirmed by pathologists' review of tissue, and 159 controls drawn from necropsy records. Controls were matched by sex, age at death and year of death. All died between January 1979 and December 1991 with an address at death in Leeds, Calderdale, York, Wakefield or Pontefract (Yorkshire, England). Of 316 potential cases, 226 were confirmed; information was obtained for 185 of them (133 by interview with relatives, 52 from coroners' records).
• Exposure: Lifetime asbestos exposure, excluding the last 15 years of life, by several routes. Occupational and household (paraoccupational) exposure were coded as likely, possible or unlikely. Residential exposure was coded as likely if the person had lived within 0.5 km of any of 278 factories in north and west Yorkshire thought to use asbestos (83 had a study subject living nearby). The fibre type used was not known for many factories; the authors report that the Leeds factory mainly used crocidolite and the Calderdale factory used crocidolite and amosite.
• Main results:
  • Likely or possible occupational exposure: 150 cases (81%) and 80 controls (50%). Adjusted OR for likely or possible versus unlikely occupational exposure: 5.6 (95% CI 3.1 to 10.1).
  • Adjusted OR for likely versus possible or unlikely occupational exposure, as read from the table: 9.1 (95% CI 4.8 to 17.1).
  • Paraoccupational exposure after excluding people with likely occupational exposure (81 cases, 124 controls): odds were higher in cases. When the 'possible' group was combined with the 'likely' group, the confidence interval (OR 1.8, 95% CI 0.87 to 3.6 as read from the table) was also consistent with equal odds.
  • Paraoccupational exposure after excluding people with likely or possible occupational exposure (34 cases, 58 controls): ORs were 61.7 (95% CI 3.4 to 1104) for likely versus other, and 5.8 (95% CI 1.7 to 19.2) for likely or possible versus unlikely, as read from the table. The authors said they could not state precisely how much the odds were raised.
  • Residential exposure: adjusted ORs ranged from 1.5 to 6.6 depending on which subjects and factory sources were included. The confidence intervals were so wide that slightly reduced or greatly increased odds could not be excluded.
  • Only 3% of cases (6 of 185) were associated solely with residential exposure. 5% of cases and 27% of controls seemed to have no asbestos exposure, a category that included people with missing information.
  • 45% of exposure histories reported asbestos exposure by more than one route.
• The authors' conclusion: The authors concluded that the results support previous evidence linking occupational and paraoccupational exposure with mesothelioma. Only 3% of cases were associated solely with residential exposure, and this study alone could not show whether residential exposure is a risk factor; a larger study is needed.
• Limitations the authors state:
  • Far fewer cases than planned lacked occupational or paraoccupational exposure: 9.7% instead of the assumed one third. This left few subjects for the residential analysis.
  • The 0.5 km radius is an arbitrary proxy for exposure from a particular source.
  • Identifying asbestos-using premises from trade directories and local knowledge may be imprecise.
  • The type of asbestos used could not be determined for many factories.
  • Exposure histories came from relatives and were of uneven quality; some informants were vague about periods of the person's life.
  • The authors assumed that occupational exposure outweighed other routes, which may not hold for every subject.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Mesothelioma, Case-Control Study, Odds Ratio, Occupational Exposure, confidence interval.

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