Background and Objective:
Many epidemiological studies have shown short-term associations between air pollutants and respiratory illnesses by considering the daily hospital admissions. However, for respiratory diagnoses hospital admissions are decreasing and emergency department visits are more frequent even if the cost per case is lower. The objective was to study the relation between air pollution levels, especially for traffic related pollutants, and respiratory emergency department visits in Greater Stockholm over a 5 year period, 2001–2005. In particular we were interested in the association for the daily number of visits for asthma (mv = 22.17, min = 0, max = 71) and asthma not specified as allergic (ICD10: J45.1 and J45.9, mv = 12.8, min = 0, max = 41).
The effect of short-term changes in air pollutants on emergency department visits were studied by using additive Poisson regression models. Models included air pollutants (lag01), terms to describe the seasonal patterns in the emergency department visits, their dependence on weather conditions, and their associations with holiday periods and influenza and pollen episodes. Pollutants included were urban background 24h mean (μg/m3) of PM10 (mv = 18, min = 4, max = 90), PM2.5 (mv = 11, min = 3, max = 47), coarse PM (PM10-PM2.5) (mv = 7, min = 0, max = 57), NOx (mv = 22, min = 4, max = 175), and 8h maximum ozone (mv = 61, min = 5, max = 127). Both single and several pollutant models (two-pollutant models with PM variables or NOx + ozone and three-pollutant models with coarse PM and PM2.5 or NOx + ozone simultaneously in the model) were considered.
For asthma and its subgroups we generally found significant associations for coarse PM and PM10, while other variables show less of an association with emergency visits for asthma. Several pollutant models showed robust effects for coarse PM.
We conclude that coarse particles, in Stockholm originating mainly from road dust, seem to worsen asthma and increase respiratory emergency department visits. There is also support for an effect of vehicle exhaust indicated by NOx.