A Case-Control Study of Airways Obstruction Among Construction Workers: Webinar PPT

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Anna Chen , John Dement , Laura S. Welch , Patricia Quinn , Scott Haas
CPWR - The Center for Construction Research and Training , Duke University Medical Center , Stoneturn Consultants , Zenith American Solutions

Summary Statement

This PowerPoint was presented by John Dement during a CPWR webinar to discuss the results of a study of COPD among construction workers. The study was published in the American Journal of Industrial Medicine (58:1083-1097, 2015) and showed that normal construction exposures to vapors, gases, dusts and fumes increase risk of COPD approximately 18%.
October 2015.

Presentation Overview

  • Review COPD and Risk Factors
  • Present Research Design & Methods
  • Review Study Results
  • Discuss Implications for Prevention


Asthma COPD
Drop in airflow that reverses with inhalers Drop in airflow that does not reverse with inhalers
Onset early in life, often childhood Onset in midlife, typically after age 50
Accompanied by allergies, rhinitis Stongly linked to smoking history
May be without any symptoms between attacks
Symptoms are persistent:
chronic cough
sputum production
shortness of breath

There is considerable overlap between asthma and COPD and individuals can have symptoms of both conditions.

Clinical COPD Diagnosis


  • Chronic cough, sputum production, shortness of breath on exertion.

Spirometry (Lung Function):

  • Post bronchodilator FEV1 < 80% predicted
  • FEV1/FVC ratio <0.70.

(FEV1 is a measure of air flow on lung function testing, FVC is a measure of lung volume)

COPD Disease in US

  • 13 million people in U.S. have diagnosed COPD.
  • >133,000 U.S. deaths due to COPD in 2010. Third leading cause of death in U.S.
  • COPD costs ~ $37.2 billion in 2004.
    • $20.9 billion in health care expenditures.
    • $7.4 billion indirect morbidity costs.
    • $8.9 billion indirect mortality costs.

Many cases of COPD may go undiagnosed for many years.
Some estimates suggest that only about 50% of actual cases in the US population have received a physician diagnosis.

COPD Risk Factors

  • Hereditary deficiency in α1-antitrypsin (ATT), a protein made in the liver.
    • Less than 1% of COPD patients have an ATT deficiency, so the population attributable risk (PAR) <1%.
  • Cigarette Smoking
    • 80-90% of COPD cases caused by smoking
    • Only 15-20% of smokers develop COPD and 10% of COPD deaths occur in lifetime non-smokers.
  • Occupational Exposures
    • 15-30% of COPD cases are estimated caused by occupational exposures overall.
    • Among never smokers, up to 50% of COPD cases estimated to be caused by occupational exposures.

Among non-smokers the occupational attributable fraction ranges from about 30-50%

Occupational Exposures and COPD Risk

  • General exposure to ‘vapors, gases, dusts, and fumes’ (VGDF)
  • Specific exposures known to cause COPD:
    • Coal dust
    • Welding
    • Silica
    • Diesel exhausts
    • Cement dust
    • Spray painting with isocyanate-based paints
    • Wood dust
    • Cadmium

Cigarette smoking is a major risk factor for COPD.

15-30% of COPD cases are estimated to be caused by smoking.

Most studies have considered the combination of all vapors, gases, dusts, and fumes in accessing the risk of COPD.

Some studies have looked at specific exposures and COPD. The materials in this slide show associations with specific agents from the literature.

Case-Control Study Design

This was a case-control study design. Begins with identification of workers with COPD (cases) and those who don’t have COPD (controls). Lifetime exposures are then assessed through various means including records, questionnaires, etc. The outcome measure and the measure of risk is called the odds-ratio. An odds-ratio measures the probability of exposure for cases versus controls. A value of 1.0 means the cases have the same risk as controls and values greater than 1.0 shows increased risk.

Case Control Design Model

Building Trades National Medical Screening Program

The study population for this study was drawn from workers participating in the Building Trades National Medical Screening (BTMed). The Center for Construction Research and Training(CPWR) operates and manages the BTMed program which is funded by the U.S. Department of Energy. The primary objective of BTMed is to provide well designed occupational health examinations former construction trades workers at Department of Energy sites across the US. BTMed has expanded since starting in in 1996 and currently includes over 20 sites across the US.

Map of BTMed centers across the US


Study Population and Case Definition

  • Study Base: Workers with medical exams through the Building Trades National Medical Screening Program (BTMed) through December 2013.
  • COPD Cases: Workers with a FEV1/FVC ratio below the lower limit of normal (LLN) using the prediction equations of Hankinson et al. [1999].

Selection of Controls

  • Controls were drawn from the same BTMed population as COPD cases but without COPD by the spirometry case definition.
  • Controls were randomly selected and frequency matched to the distribution of cases by gender, age (± 5 years), race, and DOE site.
  • Controls were over sampled in order to increase study statistical power.

Controls were not matched on trade as trade is a strong predictor of exposures. Controls were frequency matched by DOE site to allow control for local environmental conditions that might contribute to COPD risk. Statistical power is the ability of a study to detect increased risks that actually exists and takes into consideration random error.

Exposure Assessment Questionnaire

  • Individuals volunteered and participated after giving informed consent.
  • The telephone interview collected information concerning:
    • Jobs held more than 6 months.
    • Frequency (none to daily) of performing 90 construction-related tasks producing exposures to VGDF.
    • Exposures to VGDF in non-construction jobs, in military service, and as a bystander to other worker’s tasks.
    • Frequency of exposure to other materials associated with respiratory diseases from the literature (i.e. coal dust, pesticides, etc.).

The exposure questionnaire was developed an pilot tested in several ways including focus groups for worker input. Cases and controls were randomly assigned to trained interviewers. Interviewers were blind as to case or control status.

Cumulative Exposure Indices

  • Data from the questionnaire were used to develop lifetime cumulative indices for 15 exposures known to cause COPD, plus VGDF.
  • Indices included task frequency, job duration, work hours per week, and task exposure intensity.
  • Task exposure intensity was developed based on scores by 3 experienced industrial hygienists.
  • Indices included construction, non-construction, military, and bystander exposures.

Exposure indices should be considered qualitative estimates of lifetime exposures.

Lifetime Exposures Assessed

Agent or exposure
Reference concentration
for intensity scoring
Asbestos 2 f/cc
Silica 0.1 mg/m3 respirable
Cement dust 5 mg/m3 respirable
Man-made-mineral-fibers 1f/cc
Engine Exhausts 100 µg/m3 respirable elemental carbon
Acids Ceiling 5 ppm as HCL
Caustics Ceiling 2 mg/m3 as sodium hydroxide
Welding, thermal cutting, soldering, or brazing 5 mg/m3 as total aerosol
Metal cutting, grinding, and machining aerosol 5 mg/m3 as total aerosol
Paint-related aerosols 1 mg/m3 as total aerosol 
Isocyanates 0.02ppm
Organic solvents 100 ppm as toluene
Wood dust 1 mg/m3 as total aerosol
Molds and spores Exposure above typical background
Particulates not otherwise regulated (PNOR) 10 mg/m3 as total aerosol

A cumulative measure of all VGDF exposures was developed as the sum of the exposure indices for the 15 a priori agents. Reference concentrations were used to better standardize scoring of exposure intensities by industrial hygienists.

COPD Study Participation Summary

Participation measure Cases Controls
Sent invitation letters 1612 2129
Contacted, completed interview
83 1245
Contacted, declined interview
130 200
Not contacted
648 684
Reason for no contact
238 137
No Telephone contact1
410 547
Overall participation rate among living 60.6% 62.5%
Overall participation rate among those contacted 86.5% 86.3%
1Case and control distribution by site not significantly different, Chi-Square= 7.47, p=0.76

The overall participation rate for workers contacted was over 86%.

COPD Cases and Controls by DOE Site

DOE Site Description1 Cases
Brookhaven National Laboratory 19 29 48
Fernald Feed Materials Production Center (FMPC) 137 18 320
General Electric Company, Cincinnati 23 39 62
Hanford 167 224 391
Idaho National Engineering and Environmental Laboratory 55 66 121
Kansas City Plant 37 53 90
Mallinckrodt Chemical/Weldon Spring 10 14 24
Oak Ridge (All Sites) 114 195 309
Paducah Gaseous Diffusion Plant 44 58 102
Portsmouth Gaseous Diffusion Plant 54 92 146
Rocky Flats Plant 62 101 163
Savannah River Site 112 189 301
1Case and control distribution by site not significantly different, Chi-Square= 7.47, p=0.76
2Two workers were not included in the analyses due to missing data on key a variable.

Cases and controls were drawn from many DOE sites.  As cases and controls were matched by DOE site, the distribution by case of control status among the study participants was similar and not statistically different.

COPD Cases and Controls by Trade

Trade Group or Job1 Cases
Asbestos Worker or Insulator 25 37 62
Boilermaker 16 27 43
Carpenter 55 77 132
Cement Mason/Brick Mason/Plasterer 23 12 35
Electrician 128 226 354
Elevator Constructor 1 5 6
Ironworker 50 64 114
Laborer 115 152 267
Machinist 3 6 9
Mechanical Trades 7 8 15
Millwright 14 19 33
Operating Engineer 53 81 134
Painter 29 30 59
Plumber, Steamfitter, Pipefitter 130 200 330
Roofer 13 9 22
Security 4 5 9
Sheetmetal Worker 45 82 127
Sprinkler Fitter 8 8 16
Teamster 32 34 66
Welder 1 13 14
All Other Construction and Non-Construction 82 148 230
1Case and control distribution by trade significantly different, Chi-Square=33.09, p=0.033

The study included many construction trades, which provided workers with varied exposures. This was important and allowed us to observe exposure contrasts when cases and controls were compared.

Characteristics of Cases and Controls

Characteristic Cases (n=834) Controls (n=1243)2
Mean age (SE) 62.3 (0.37) 62.7 (0.30)
Male sex (%) 764 (91.6) 1152 (92.7)
Non-white race or Hispanic ethnicity (%) 76 (9.1) 118 (9.5)
History of Physician Diagnosed Respiratory Conditions(%)
192 (23.1)* 114 (9.2)
Chronic bronchitis
169 (20.3)* 103 (8.3)
185 (22.2)* 49 (3.9)
242 (29.1)* 241 (19.4)
symptoms (%)
418 (50.1)* 353 (28.4)
393 (47.1)* 337 (27.2)
Shortness of Breath
469 (56.3)* 386 (31.1)
Spirometry, Mean (SE)
% Predicted FVC
81.3 (0.70)* 87.7 (0.46)
% Predicted FEV1
62.9 (0.67)* 89.7 (0.49)
0.58 (0.003)* 0.77 (0.002)
Chest X-ray B-Reader prevalence (%)(N=2057)
Pleural changes only
120 (14.6) 179 (14.5)
Parenchymal changes only (Profusion ≥1/0
20 (2.4) 23 (1.9)
Both Pleural and Parenchymal
23 (2.8) 28 (2.3)
History of hypertension (%) (N=2076) 262 (31.5)* 331 (26.6)
History of congestive
heart disease (%) (N=2074)
27 (2.8)* 23 (2.1)
History of severe
childhood pneumonia (%)
31 (3.7) 47 (3.8)
Smoking Status (%)
Current smoker
236 (28.3)** 138 (11.1)
Past smoker
462 (55.4) 632 (50.8)
Never smoker
136 (16.3) 473 (38.1)
Mean Cigarrette pack-years (SE) 31.3 (0.88)* 15.6 (0.56)
Mean Body Mass Index (SE) 29.2 (0.20)* 30.5 (0.15)
Family history of COPD (%) 212 (25.4)* 230 (15.5)
*Cases and controls significantly different, p<0.05
**Chi square overall measure of association across categories

Cases and controls did not differ significantly with respect to matching variables (age, gender, race/ethnicity).
As expected, controls had a significantly greater history respiratory conditions including asthma, chronic bronchitis, emphysema, and pneumonia as well as respiratory symptoms associated with COPD.
Spirometry followed the COPD case definition.

Study Results – Overall Associations

  • Logistic regression models adjusted for age, gender, race/ethnicity, smoking, BMI, and having a blood relative with COPD.
  • Smoking was a strong risk factor for COPD.
  • Exposures to the 13 of the 15 materials previously reported to cause COPD, and all VGDF combined, were significantly associated with COPD.
    • Exposures to man-made mineral fibers and paint-related aerosols did not reach statistical significance.
  • Workers who entered construction work after 1980 continued to experience increased COPD risk related to the exposures evaluated.

All analyses were based on unconditional logistic regression.

COPD Odds-Ratios Exposure Index

  Odds-ratio (95%CI) by fraction of upper 95th percentile d
Exposure Index
0.25 0.50 0.75 1.00





Silica 1.21
Acids and
Isocyanates 1.09
Molds and
not otherwise
All VGDF 1.19
Logistic regression model adjusted for age, gender, race/ethnicity, smoking status (Current, Past, Never), cigarette pack-years, family history of COPD, and BMI.

Odds-ratios are a measure of risk. A value of 1.0 means no increased risk and values >1.0 indicate increased risk.
All a priori exposures except man-made mineral fibers and paint-related aerosols were significantly associated with COPD risk.
The relationships in the models were best described and linear except for acids and caustics and wood dust. These materials suggested a flattening the of the exposure response at higher cumulative exposures.
All VGDF exposures combined was a strong and consistent predictor of COPD risk.
PNOR exposures were strongly predictive of risk.

Occupational Attributable COPD

  • Overall, 18% (95% CI=2-24%) was attributable to occupational VGDF exposures.
  • Among never smokers 32% (95% CI=6-42%) was attributable to occupational VGDF exposures.
  • Cigarette smoking and occupational exposures were approximately additive.


  • Construction workers are at significantly increased risk of COPD.
  • Workers employed after 1980 continue to be at risk.
  • Construction exposures are complex and COPD risk is strongly related to exposure to all VGDF combined.
  • 18% of COPD cases overall and 32% among never smokers is attributable to VGDF exposures.
  • Regulatory approaches need to consider combined effects of all VGDF exposures.
  • Exposures to PNOR, while correlated with other exposures, increase the risk of COPD.
  • Current regulatory standards in the US for respirable PNOR (5 mg/m3) may not be sufficient to prevent COPD.

Publication Availability

This study is published in the American Journal of Industrial Medicine and is available as an open access (free) publication.

Dement J, Welch L, Ringen K, Quinn P, Chen A, Haas S. 2015. A case-control study of airways obstruction among construction workers. Am J Ind Med. 58:1083-1097.


John Dement, PhD,1 Laura Welch, MD,2 Knut Ringen, Dr. PH,2,3 Patricia Quinn, BA,2 Anna Chen, BS,4 and Scott Haas, MJ4

1 Division of Occupational & Environmental Medicine, Duke University Medical Center
2 The Center for Construction Research and Training(CPWR)
3 Stoneturn Consultants
4 Zenith American Solutions

This study was funded by the National Institute for Occupational Safety and Health (NIOSH)

Grant Number: 5R01OH009943
PI: John M. Dement


We greatly appreciate the many individuals who contributed to this study.

  • Participants who gave of their time to further knowledge of COPD and causes.
  • Our interviewers Ron Bush, Andy Noel, Johnny Ballinger, and Dan Obray.
  • Drs. Carol Rice and Robert Herrick for their assistance with the exposure intensity scoring.
  • Patricia Worthington (DOE) and Mary Fields (DOE) for their support of this project.

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