title: Occupational COPD and job exposure matrices: a systematic review and meta-analysis.
abstract: BACKGROUND
  The association between occupational exposure and COPD reported previously has mostly been derived from studies relying on self-reported exposure to vapors, gases, dust, or fumes (VGDF), which could be subjective and prone to biases. The aim of this study was to assess the strength of association between exposure and COPD from studies that derived exposure by job exposure matrices (JEMs).
  
  
  METHODS
  A systematic search of JEM-based occupational COPD studies published between 1980 and 2015 was conducted in PubMed and EMBASE, followed by meta-analysis. Meta-analysis was performed using a random-effects model, with results presented as a pooled effect estimate with 95% confidence intervals (CIs). The quality of study (risk of bias and confounding) was assessed by 13 RTI questionnaires. Heterogeneity between studies and its possible sources were assessed by Egger test and meta-regression, respectively.
  
  
  RESULTS
  In all, 61 studies were identified and 29 were included in the meta-analysis. Based on JEM-based studies, there was 22% (pooled odds ratio =1.22; 95% CI 1.18-1.27) increased risk of COPD among those exposed to airborne pollutants arising from occupation. Comparatively, higher risk estimates were obtained for general populations JEMs (based on expert consensus) than workplace-based JEM were derived using measured exposure data (1.26; 1.20-1.33 vs 1.14; 1.10-1.19). Higher risk estimates were also obtained for self-reported exposure to VGDF than JEMs-based exposure to VGDF (1.91; 1.72-2.13 vs 1.10; 1.06-1.24). Dusts, particularly biological dusts (1.33; 1.17-1.51), had the highest risk estimates for COPD. Although the majority of occupational COPD studies focus on dusty environments, no difference in risk estimates was found for the common forms of occupational airborne pollutants.
  
  
  CONCLUSIONS
  Our findings highlight the need to interpret previous studies with caution as self-reported exposure to VGDF may have overestimated the risk of occupational COPD.
authors.affiliation: Institute of Occupational and Environmental Medicine, University of Birmingham, Edgbaston, Birmingham.
authors.forename: Steven
authors.initials: S
authors.lastname: Sadhra
authors.affiliation: Nuffield Department of Population Health, Clinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, Oxford, UK.
authors.forename: Om P
authors.initials: OP
authors.lastname: Kurmi
authors.affiliation: Institute of Occupational and Environmental Medicine, University of Birmingham, Edgbaston, Birmingham.
authors.forename: Sandeep S
authors.initials: SS
authors.lastname: Sadhra
authors.affiliation: Nuffield Department of Population Health, Clinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, Oxford, UK.
authors.forename: Kin Bong Hubert
authors.initials: KB
authors.lastname: Lam
authors.affiliation: Institute of Occupational and Environmental Medicine, University of Birmingham, Edgbaston, Birmingham.
authors.forename: Jon G
authors.initials: JG
authors.lastname: Ayres
mesh_terms: D000395:Air Pollutants, Occupational / Q000009:adverse effects*; D015982:Bias; D004391:Dust; D005260:Female; D005740:Gases; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects*; D008297:Male; D009784:Occupational Diseases / Q000175:diagnosis / Q000209:etiology*; D016273:Occupational Exposure / Q000009:adverse effects*; D016272:Occupational Health; D009790:Occupations; D016017:Odds Ratio; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000209:etiology*; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors
chemical_list: D000395:Air Pollutants, Occupational; D004391:Dust; D005740:Gases
keywords: COPD; airborne substances; job exposure matrices; occupation