Ascertaining the risk of chronic obstructive pulmonary disease in relation to occupation using a case-control design

Recent community surveys have reported a risk of chronic obstructive pulmonary disease (COPD) in occupations involving exposure to organic dust and gas/vapour. Aims Our aim was to confirm these results using a case-control design on 131 COPD cases (FEV(1) < 80% of predicted value, minimally reversible with bronchodilators) and 298 controls, selected from registers for patients admitted to our Institute of Occupational Medicine.

Surrogates of past exposure were occupation, exposure assigned by a job-exposure matrix, and years spent in a given occupation. The odds ratio (OR) and 95% confidence interval (CI) for COPD were calculated using logistic regression models with office workers as the reference.

Age-smoking-adjusted ORs (and CIs) were: 15.1 (3.2-71.6) in farmers; 7.2 (1.3-41.1) in cotton workers; 6.4 (1.6-25.5) in welders; 4.7 (1.3-16.4) in painters; 12.1 (1.3-108) in foundry workers; 6.50 (1.14-37.0) in refractory brick workers; and 3.1 (1.0-9.5) in construction workers. In farmers, cotton workers, welders and painters, the adjusted ORs significantly increased (by 6-9%) for each extra year of work, while in other occupations any such increase was of borderline significance. Adjusted ORs were 3.80 (1.21-12.0), 5.83 (1.82-18.6) and 8.86 (2.29-34.3) in workers exposed to high levels of mineral dust, gas/vapour/fume and biological dust, respectively. Consistent risk estimates were obtained for farmers, textile workers, painters and welders.

Our findings confirm previous epidemiological evidence and are supported by recent observations that cigarette smoke, cotton and organic farm dust contain the same powerful pro-inflammatory agents, and that organic dust and irritant gas induce bronchitis by triggering the same effector molecules as cigarette smoke.