Social disadvantage, air pollution, and asthma physician visits in Toronto, Canada

Background — Previous research demonstrates that ambient air pollution exacerbates asthma. Asthma morbidity also varies with socioeconomic position (SEP). Few studies have examined if ambient air pollution has a differential impact on income subgroups of the population. This paper investigates socioeconomic variation in ambulatory physician consultations for asthma and assesses possible effect modification of SEP on the association between physician visits and air pollution for children aged 1–17 and adults aged 18–64 in Toronto, Canada, between 1992 and 2001.

Methods — Generalized additive models and generalized linear models were used to estimate the adjusted risk of asthma physician visits associated with an interquartile range increase in sulfur dioxide (SO2), nitrogen dioxide (NO2), particulate matter (PM2.5), and ozone (O3).

Results — A socioeconomic gradient in the number of physician visits was observed among children and adults and both sexes. SO2, NO2, and PM2.5 had positive associations with physician visits. The risk ratios for the low socioeconomic group were significantly greater than those for the high socioeconomic group in several of the models of SO2 and PM2.5.

Conclusions — These findings suggest increased ambulatory physician visits represent another component of the public health impact of urban air pollution. The burden of this impact may be borne disproportionately by those with lower SEP. Clarifying the role of SEP in altering susceptibility to the effects of air pollution is essential not only to inform revisions of ambient air quality standards, but also to design public health interventions to reduce health impacts on sensitive subgroups of the population.