O2.1 CHRONIC OBSTRUCTIVE PULMONARY DISEASE AND EXPOSURE TO WOOD DUST

P. A. Demers, H. W. Davies, M. Friesen, C. Hertzman, A. Ostry, K. Teschke.School of Occupational & Environmental Hygiene, University of British Columbia, Vancouver, Canada

Many cross sectional studies have observed an increased prevalence of respiratory symptoms and impaired airflow associated with exposure to wood dust. However, cohort studies have generally observed a decreased risk of death due to chronic obstructive pulmonary disease (COPD) and no evidence of a dose–response relationship among workers exposed to wood dust. This could represent a true difference in the risk of disease or be due to differences in comparison populations (other workers versus the general population), disease endpoint (morbidity versus death), or quality of exposure assessment. To further evaluate the relationship between COPD and wood dust, we examined the relationship between hospitalisation for COPD and quantitative indices of exposure in a retrospective study of sawmill workers. The cohort consists of 11 424 workers from 14 lumber mills employed for one or more years after 1978. Hospital discharge records were available for the period 1985−1998. A quantitative exposure assessment was conducted for non-specific dust, wood dust, and tree species. Exposure metrics for cumulative exposure (duration and mg/m³ years) were developed. Relative risks (RR) were adjusted for sex, race, age group, and time period in internal analyses and time at risk for cases was counted until first hospitalisation for COPD. Overall, 133 members of the cohort were hospitalised with a primary diagnosis of COPD during the follow up period. No association was observed with duration of employment, although an excess risk was observed among workers with 10 to 19 years of employment relative to those with <5 years (standardised relative risk (SRR) 1.6; 95% confidence interval (CI) 0.6 to 4.7). A weak negative association was observed with non-specific dust. Higher incidence was observed among workers with 5–9 (SRR 1.4; 95% CI 0.8 to 2.6), 10−19 (SRR 1.6; 95% CI 1.1 to 3.4), and ⩾20 (SRR 1.6; 95% CI 1.0 to 2.8) mg/m³ years of exposure to wood dust relative to those with <5 mg/m³ years. The highest relative risks were observed among workers employed at three mills that processed a combination of spruce, pine, and fir. Although exposure levels were relatively low in this study, an association between wood dust and COPD was observed. The lack of a monotonic increase in risk may be due to a survivor effect.

O2.2 INTERACTION BETWEEN SOLVENT EXPOSURE AND SMOKING AS RISK FACTORS FOR COLD

N. E. Ebbehøj, H. O. Hein, P. Suadicani, F. Gyntelberg.Clinic of Occupational Medicine, H:S Bispebjerg University Hospital, Copenhagen, Denmark

This study was performed in the Copenhagen Male Study, a prospective cohort study including 3387 men aged 53–87 years to assess the interaction between occupational solvent exposure and smoking as risk factors for chronic obstructive lung disease (COLD). The retrospective exposure question addressed “several times a week” exposure to 15 occupational factors at present or former jobs, and the results dichotomised at ⩾5 years of exposure. The men classified themselves as current, previous, or never smokers. COLD was assessed from the British Medical Research Council questionnaire on respiratory symptoms, and addressed present symptoms. Additionally, a number of confounders were assessed from the questionnaire.

Results: Current smoking and the interaction of current smoking and exposure to organic solvents (>5 years), were the factors statistically most strongly associated with prevalence of COLD. Exposure to organic solvents was associated with a significantly increased prevalence of chronic bronchitis in smokers, but not in non-smokers. Age adjusted odds ratios (ORs) and 95% confidence intervals (CI) were 2.2 (1.5 to 3.2), (p<0.001) and 1.2 (0.6 to 2.3) (p = 0.65), respectively. ORs comparing smokers with non-smokers who had been exposed and unexposed to solvents were 7.0 (3.4–14.5) (p<0.001), and 3.7 (2.8–4.8) (p<0.001), respectively. The interaction of smoking and long term organic solvent exposure remained significant after controlling for a number of potential confounders.

Conclusion: The association of smoking with COLD was much stronger among men with a >5 year history of organic solvents exposure compared with those without such exposure.

O2.3 SILICOSIS PREVALENCE AND EXPOSURE RESPONSE RELATIONSHIPS IN SOUTH AFRICAN GOLDMINERS

R. I. Ehrlich¹, G. J. Churchyard², J. M. teWaterNaude¹, L. Pemba², K. Dekker³, M. Vermeis³, N. W. White¹, J. E. Myers¹.¹Occupational and Environmental Health Research Unit, University of Cape Town, South Africa; ²Aurum Health Research, Orkney, South Africa; ³Anglogold, Orkney, South Africa

Objective: To measure the prevalence of silicosis among black, primarily migrant contract workers on a South African goldmine and to investigate exposure response relationships with silica dust (quartz).

Methods: In a cross sectional study, 520 goldminers over 38 years of age were interviewed and had chest radiographs taken. Silicosis was defined as ILO Classification radiological profusion of 1/1 or greater. Cumulative exposure was calculated for each miner using time weighted average respirable dust concentrations from two sources: personal sampling of a separate group of 112 workers and a database of routine surveillance measurements. Quartz fractions were measured by x ray diffraction. The 85 different occupations among the 520 miners were reduced to 23 occupational categories with similar exposures.

Results: Mean length of service was 21.8 years (range 6.3–34.5). The mean intensity of respirable dust exposure was 0.37 mg/m³ (range 0–0.70) and of quartz 0.053 mg/m³ (range 0–0.095). The prevalence of silicosis (reader 1) was 18.3% (95% confidence interval (CI) 15.0 to 21.9) and (reader 2) 19.9% (95% CI 16.5 to 23.6). Significant trends were found between the prevalence of silicosis and length of service, mean intensity of exposure, and cumulative exposure (odds ratio 3.2; 95% CI 1.9 to 5.4).

Conclusions: The results confirm a large burden of silicosis among older migrant contract workers in the South African gold mining industry, which is likely to worsen as such miners spend longer periods in continuous employment in dusty jobs. An urgent need for improved dust control in the industry is indicated. If the assumption of stability of average dust concentrations in this mine over the working life of this group of workers is correct, these workers developed silicosis while exposed to a quartz concentration below the recommended occupational exposure limit (OEL) of 0.1 mg/m³. This accords with a mounting body of evidence that an OEL of 0.1 mg/m³ is not protective against silicosis.

O2.4 CHRONIC OBSTRUCTIVE PULMONARY DISEASE AND OCCUPATIONAL EXPOSURES IN A COMMUNITY BASED STUDY IN MELBOURNE, AUSTRALIA

M. C. Matheson¹, G. Benke¹, J. Raven², M. Sim¹, H. Kromhout³, D. P. Johns⁴, E. H. Walters⁴, M. J. Abramson¹.¹Epidemiology and Preventive Medicine, Monash University; ²Allergy, Immunology & Respiratory Medicine, The Alfred, Melbourne; ³Occupational and Environmental Health, Utrecht University, The Netherlands; ⁴School of Medicine, University of Tasmania, Australia

Introduction: Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality. The major risk factor for COPD is smoking; however, up to 15% of COPD may be attributed to occupational exposure.

Objective: To establish the contribution of occupational exposure to COPD among the general population in Melbourne.

Methods: Participants were part of a cross sectional study of risk factors for COPD. A total of 1232 participants completed a detailed respiratory questionnaire, spirometry, and measurement of gas transfer (T_LCO) by the single breath technique. Job histories were elicited from subjects and coded according to the International Standard Classification of Occupations codes. These codes were then used to establish occupational exposures using a job exposure matrix called ALOHA.

Results: The mean (SD) age of subjects was 57.8 (7.5) years and 51.7% were male. The prevalence of emphysema was 4.0%, chronic bronchitis 1.8%, and COPD 4.8%. Subjects occupationally exposed to biological dusts had increased risk of chronic bronchitis (odds ratio (OR) 3.35; 95% confidence interval (CI) 1.34 to 8.4), emphysema (OR 2.77; 95% CI 1.5 to 5.13), and COPD (OR 2.6; 95% CI 1.48 to 4.51). Overall exposure to any gases/vapours/dusts/fumes at work was associated with an increased risk of chronic bronchitis (OR 4.30; 95% CI 1.25 to 14.6), emphysema (OR 2.16; 95% CI 1.09 to 4.26), and COPD (OR 2.25; 95% CI 1.20 to 4.23).

Conclusion: In this general population sample of adults, we found occupational exposure to biological dusts to be associated with increased risk of COPD. Preventive strategies should be aimed at reducing exposure to these agents in the workplace.

Acknowledgemets: Supported by NHMRC, Windermere Foundation, and VTLA.

O2.5 HRCT ASSESSMENT OF SILICOSIS AND EMPHYSEMA IN CONSTRUCTION WORKERS: A CASE–CONTROL STUDY

E. T. Nij¹, E. Meijer¹, M. van der Drift¹, G. de Meer¹, J. S. van der Zee², T. Kraus⁵, C. van Duivenbooden⁴, J.-WLammers³, D. Heederik¹.¹Institute for Risk Assessment Sciences, University Utrecht; ²AMC Amsterdam; ³UMC Utrecht; ⁴ARBOUW Utrecht, The Netherlands, ⁵IOCOM, Aachen, Germany

Introduction: Mixed dust pneumoconiosis was observed in a baseline study in 1998 among 1335 construction workers.¹ Few workers had rounded opacities, the prevalence of individuals with irregular opacities was high, and agreement between readers was low.

Objective: We therefore wanted to evaluate quartz dust associated radiological changes in construction workers using more advanced diagnostic techniques and re-analyse exposure–response relationships.

Methods: High resolution computed tomography (HRCT) (n = 79), chest x rays (n = 93), and dynamic and static lung volumes and gas diffusion parameters (n = 96) were determined in construction workers with and without radiological abnormalities at baseline.

Results: Rounded opacities on HRCT (n = 13) and chest x ray (n = 11), and pleural abnormalities (n = 29) were clearly associated with elevated cumulative quartz dust exposure, but not with smoking. Odds ratios (95% confidence intervals) were respectively 5.9 (1.0 to 3.5), 4.7 (0.82 to 27), and 4.9 (1.3 to 19) for the highest exposure groups. Reduced FEV₁, T_LCO,sb, and K_CO were mainly associated with emphysematous changes in the lungs, while the presence of irregular opacities on HRCT was associated with obstructive (group based reduction in FEV₁: 9.1%) and restrictive lung function changes, but not with cumulative quartz exposure or smoking. Occurrence of emphysema was strongly associated with smoking habits.

Conclusion: Silicosis in construction workers, as diagnosed by the presence of rounded opacities, could be observed on both HRCT and chest x ray. The presence of mixed dust pneumoconiosis associated with quartz dust as previously observed could not be reconfirmed.

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