A historical mortality study among bus drivers and bus maintenance workers exposed to urban air pollutants in the city of Genoa, Italy

Objective A historical mortality cohort study was conducted in Genoa, Italy among public transport workers ever employed between 1949 and 1980, to estimate overall and cause-specific mortality from January 1970 to December 2005 and to examine associations between exposure to urban air pollutants and overall and cause-specific mortality. Methods Causes of death for 9267 males (6510 bus drivers, 2073 maintenance workers and 601 white collar workers) were coded according to ICD-9. Standardised mortality ratios (SMRs) and 95% CIs were computed by applying Italian and regional male death rates to person-years of observation for the entire cohort and following stratification by longest held job title and length of and time since first employment using the Poisson regression model. Results There were 2916 deaths and 230 009 person-years of observation; 17 subjects were lost to follow-up. SMRs for all causes, diseases of the circulatory, respiratory, digestive and genitourinary systems, and for accidents were lower than expected. SMRs (95% CI) were increased for lung cancer (1.16, 1.05 to 1.28), non-Hodgkin's lymphoma (1.23, 0.85 to 1.78), Hodgkin's lymphoma (2.14, 1.19 to 3.87) and diabetes mellitus (1.16, 1.05 to 1.28). The SMR for leukaemia was 0.77 (0.51 to 1.16). Hodgkin's lymphoma mortality was significantly increased among bus drivers (1.62, 1.37 to 5.04). Lung cancer risk was significantly increased among all workers after 30 years' employment and among maintenance workers. Conclusions The study failed to show any increased risk for leukaemias. The increased mortality from Hodgkin's lymphoma and lung cancer may be associated with long-term exposure to urban air pollution.