A study of the relationship between vehicle emissions and respiratory health in an urban area

A multi-group ecologic study design is used to investigate the relationship between exposure to particulate matter from vehicle emissions and the rate of respiratory hospital admissions. The study is performed at the level of the census enumeration area (EA) in Southeast Toronto. This 16-km² urban area contains 335 EAs ranging in population from 45 to 1255 people. Overall, the area contains 122 830 people and has a diverse socio-demographic profile. The response variable is the indirectly age-adjusted three-year (1990-1992) respiratory hospitalization rate and the exposure variable is the 12-hour average (1987-1991) exposure to particulate matter (PM). Hospitalization rates are calculated from discharge summary data, and PM exposure is modeled from traffic count data with a geographical information system. A modified Jarman social disadvantage index calculated from the 1991 census is modeled as a covariate. Univariate maps are used to describe spatial distributions. Multiple linear regression and Poisson regression are used to examine relationships between variables. Findings provide limited support for previous observations that vehicle emissions may adversely affect the respiratory health of humans. Study design and measurement issues limit the ability of this study to further characterize the observed relationship.