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UBC Theses and Dissertations

Lung cancer and COPD among sawfilers and those exposed to endotoxin while working in BC sawmills Chen, Hanchen


Background: Sawfilers are a sub-group of sawmill workers who repair and maintain saw blades, and are exposed to multiple inhalable occupational hazards some of which were carcinogens or have non-malignant respiratory effects. Sawmill workers in general may be exposed to endotoxins from gram-negative bacteria of the wood. Previous studies across different industries have shown that endotoxin would increase the risk of COPD, but may decrease the risk of lung cancer. The main goal of this thesis was to examine the associations between the two exposures (sawfiling employment and endotoxin) and two diseases (lung cancer and COPD) by using an existing cohort of 25,685 BC sawmill workers. Method: Sawfiling exposure was categorized into ever-exposed and never-exposed groups. For endotoxin, we used a previous endotoxin monitoring study of 216 samples in BC sawmills to build a predictive model through forward-stepwise linear regression, based on which we assigned quantitative endotoxin exposure values and calculated cumulative endotoxin exposure levels. Relative risk of lung cancer (ICD9=162) and COPD (ICD9=490,491,492,496) for each exposure group were assessed using Poisson regression, controlling for age, race, calendar period, and time since first exposure, with workers in lowest exposed category as the reference. Results: A total of 523 cases of lung cancer (follow-up period 01/01/1959 to 12/31/1995) and 120 cases of COPD (follow-up period 01/01/1985 to 12/31/1998) were included in the analysis. With respect to sawfiling, risk of lung cancer (lagged 20 years) and COPD (lagged 5 years) were slightly elevated (RR=1.4, 95% CI=0.9-2.2 and RR=1.3, 95% CI=0.6-2.5, respectively) but neither significantly. Decreased risk of lung cancer was observed among subjects with highest endotoxin exposure (RR=0.8, 95% CI=0.5-1.1), and the dose-response trend was borderline significant (p=0.059). Increased risk of COPD was observed among subjects with highest endotoxin exposure (RR=1.9, 95% CI=1.0-3.7), and the dose-response relationship was again borderline significant (p=0.065). Conclusion: This study provided evidence of a link between cumulative endotoxin exposure and a decreased trend of lung cancer and an increased trend of COPD. However, the association between lung cancer, COPD and sawfiling employment remained unclear.

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