Lung and bladder cancer among Danish urban bus drivers and tramway employees: a nested case-control study

Background The combustion of fossil fuels produces small amounts of mutagenic and carcinogenic compounds. We investigated the association between employment and lung and bladder cancer in Danish bus drivers and tramway employees. Methods We carried out a nested case-control study of 153 lung and 84 bladder cancer cases, and 606 controls sampled in a cohort of 18 174 bus drivers or tramway employees employed in Copenhagen during the period 1900-1994. The cases and controls or their next of kin were interviewed about smoking, along with occupational and residential history. An exposure index based on which bus routes the bus drivers had mainly been driving was established. Relative risks (RRs) were estimated by conditional logistic regression. Results The analysis showed decreasing risk for lung cancer with increasing years of employment as a bus driver (RR=0.97 for each added year, 95% confidence interval=0.96-0.99). The air pollution index based on main bus for the bus drivers showed no positive correlation with risk.