Air quality impacts mortality in acute medical admissions

Air quality degraded by black smoke (particulate matter, PM10), sulphur dioxide (SO2) and nitrogen oxide (NO(x)) affects human health. Improvements following national legislation have lowered death rates. Whether background air pollution levels continue to affect human health remains unclear.

To determine impact of air pollutant concentrations (PM10, SO2 and NO(x)) on in-hospital mortality for acute medical admissions to St James's Hospital over a decade (2002-11).

All emergency admissions (55,596 episodes in n = 32,581 patients) were tracked prospectively and mortality assessed. Daily levels of PM10, SO2 and NO(x) were obtained from monitoring stations in our catchment area.

Univariate and multivariate logistic regression was employed to examine relationships between pollutant concentration and odds ratio (OR) for death following adjustment for other mortality predictors.

Mortality related to each pollutant variable assessed (as quintiles of increasing atmospheric concentration) was significantly predictive. For PM10 and SO2, mortality in the highest three quintile concentrations (compared with base quintile) was significantly increased (P < 0.001) with univariate ORs of 1.24, 1.36 and 1.25 for PM10 and 1.43, 1.54 and 1.58 for SO2, respectively. Mortality in all quintile concentrations (compared with base quintile) was significantly increased (P < 0.05) for NO(x) with univariate ORs of 1.14, 1.18, 1.28 and 1.35, respectively. Following adjustment for other mortality predictors such as acute illness severity, all three air pollutants were independently predictive of mortality.

Despite improvement to air quality in Dublin, the prevailing background pollutant concentrations continue to affect human health at levels considered safe and below that previously recognized.