Non-occupational exposure to asbestos and risk of pleural mesothelioma: review and meta-analysis

Our plain-English summary of Non-occupational exposure to asbestos and risk of pleural mesothelioma: review and meta-analysis, by G.M. Marsh, A.S. Riordan, K.A. Keeton, et al (Occupational and Environmental Medicine, 2017).

The study

• Authors: G.M. Marsh, A.S. Riordan, K.A. Keeton, S.M. Benson
• Journal: Occupational and Environmental Medicine
• Published: 2017;74(11):838-846
• Type of article: Meta-analysis, Review
• Cited by: 47 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To conduct an updated literature review and meta-analysis of studies of pleural malignant mesothelioma (PMM) risk among persons exposed to asbestos non-occupationally (household and neighbourhood).

Methods: We performed a literature search for articles available in the National Center for Biotechnology Information's PubMed database published between 1967 and 2016. Meta-analyses were conducted to calculate pooled PMM risk estimates, stratifying for household or neighbourhood exposure to asbestos and/or predominant asbestos fibre type (chrysotile, amphibole or mixed).

Results: Eighteen studies in 12 countries comprising 665 cases met the meta-analysis inclusion criteria. We identified 13 estimates of PMM risk from neighbourhood exposures, 10 from household and one from mixed exposure, and combined the estimates using random-effects models. The overall meta-relative risk (meta-RR) was 5.9 (95% CI 4.4 to 8.7). The meta-RRs for household and neighbourhood exposures were 5.4 (95% CI 2.6 to 11.2) and 6.9 (95% CI 4.2 to 11.4), respectively. We observed trends in risk in relation to fibre type for both household and neighbourhood studies. For chrysotile, mixed and amphibole fibres, respectively, meta-RRs for neighbourhood studies were 3.8 (95% CI 0.4 to 38.4), 8.4 (95% CI 4.7 to 14.9) and 21.1 (95% CI 5.3 to 84.5) and meta-RRs for household studies were 4.0 (95% CI 0.8 to 18.8), 5.3 (95% CI 1.9 to 15.0) and 21.1 (95% CI 2.8 to 156.0).

Conclusions: PMM risks from non-occupational asbestos exposure are consistent with the fibre-type potency response observed in occupational settings. By relating our findings to knowledge of exposure-response relationships in occupational settings, we can better evaluate PMM risks in communities with ambient asbestos exposures from industrial or other sources.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

In plain English

This review and meta-analysis pooled earlier studies. The authors searched PubMed (1967 to 2016) and included 18 studies from 12 countries, with 665 pleural mesothelioma cases, on asbestos exposure outside work. This covered household exposure, including take-home dust from asbestos jobs, and neighbourhood exposure near industrial or natural sources. Across all 24 estimates the pooled relative risk was 5.9 (95% CI 4.1 to 8.7 in the results; 4.4 to 8.7 in the abstract). It was 5.4 (95% CI 2.6 to 11.2) for household and 6.9 (95% CI 4.2 to 11.4) for neighbourhood exposure. For neighbourhood exposure, pooled risks were 3.8 for chrysotile (95% CI 0.4 to 38.4, not statistically elevated), 8.4 for mixed fibres (95% CI 4.7 to 14.9) and 21.1 for amphibole (95% CI 5.3 to 84.5). For household exposure, mixed fibres gave 5.3 (95% CI 1.9 to 15.0). Chrysotile and amphibole had one study each, so they were not pooled. The authors concluded these risks were consistent with the fibre-type pattern seen at work. They noted large between-study differences, few pure-fibre studies, and possible exposure misclassification and misdiagnosis.

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: Literature review and meta-analysis of published epidemiological studies (ecological, case-control and cohort studies), combined using random-effects models
• Who was studied: 18 published studies from 12 countries, together comprising 665 pleural mesothelioma cases, found in PubMed for 1967 to 2016 (4 ecological, 10 case-control, 4 cohort studies)
• Exposure: Non-occupational asbestos exposure, grouped by predominant fibre type (chrysotile, amphibole or mixed). Household exposure covered products in the home or take-home dust from family members' jobs. Neighbourhood exposure covered living close to industrial or environmental sources.
• Main results:
  • All 24 effect estimates combined gave a meta-RR of 5.9, statistically significant. The 95% CI is 4.1 to 8.7 in the results section; the abstract gives 4.4 to 8.7.
  • Household exposure: meta-RR 5.4 (95% CI 2.6 to 11.2). Neighbourhood exposure: meta-RR 6.9 (95% CI 4.2 to 11.4).
  • Neighbourhood studies by fibre type: mixed fibres meta-RR 8.4 (95% CI 4.7 to 14.9), chrysotile 3.8 (95% CI 0.4 to 38.4), amphibole 21.1 (95% CI 5.3 to 84.5).
  • Household studies with mixed fibres: meta-RR 5.3 (95% CI 1.9 to 15.0), statistically significant.
  • Household chrysotile and household amphibole each had only one study, so no pooled figure was calculated. The single-study results reported were chrysotile OR 4.0 (95% CI 0.8 to 18.8; McDonald and McDonald) and amphibole OR 21.1 (95% CI 2.8 to 156.0; Yazicioglu et al).
  • Pooled risk for amphibole-only exposure was 2.5 to 3.2 times that for mixed fibres and 5.3 to 5.6 times that for chrysotile alone (neighbourhood and household respectively).
  • Chrysotile fibres did not show a statistically elevated risk of pleural mesothelioma.
  • Leaving out the crude (unadjusted) estimates or the ecological studies did not change the overall findings.
• The authors' conclusion: The authors concluded that pleural mesothelioma risks from non-occupational asbestos exposure are consistent with the fibre-type potency pattern seen in occupational settings. They also noted considerable heterogeneity between studies and small numbers of pure-fibre studies.
• Limitations the authors state:
  • There were few studies of pure fibre types, so the fibre-type meta-analyses were based on small numbers.
  • Seven crude (unadjusted) effect estimates were included.
  • Seven effect estimates rested on 10 or fewer cases.
  • Some studies did not confirm mesothelioma diagnoses histologically, and misdiagnosis could inflate risk estimates.
  • Few studies measured actual exposure levels, so exposure may have been misclassified.
  • Recall bias is possible, because most case-control studies did not interview the cases directly.
  • The pooled estimates most likely overestimate risk from non-occupational exposure, because the groups studied had higher exposure than people in places without specific asbestos sources.
  • Comparison with national or world rates could bias some studies' estimates.
  • Ecological studies were included.

Topics

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

Medical terms in this study, explained in our Lexicon: Non-Occupational Exposure, Pleural Mesothelioma, Meta-Analysis, Malignant Mesothelioma, Chrysotile, Amphibole Group, Relative Risk, Asbestos Exposure.

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