BACKGROUND--Several studies have assessed the association between urban air pollutants and hospital admissions or emergency room visits for asthma with inconsistent results. The objective of this study was to assess the relation between levels of black smoke, sulphur dioxide, nitrogen dioxide, and ozone and adult emergency room visits for asthma in Barcelona, Spain during the five year period 1985-9. METHODS--The daily number of emergency room visits for asthma was obtained from a register of respiratory emergencies designed to study the asthma outbreaks occurring in Barcelona. The association between asthma visits and levels of pollutants was assessed separately for summers and winters with Poisson regression models controlling for meteorological and time related variables. RESULTS--Black smoke was associated with asthma visits in summer but not in winter. The relative risk (RR) of asthma visits for a 25 micrograms/m3 increase of current day concentrations of black smoke was 1.082 (95% CI 1.011 to 1.157). The mean current and previous three day levels of black smoke led to a stronger association (RR = 1.114 (95% CI 1.010 to 1.160). In addition, nitrogen dioxide was associated with asthma visits in both summer (RR = 1.045, 95% CI 1.009 to 1.081) and winter (RR = 1.056, 95% CI 1.011 to 1.104). These associations were slightly higher for the previous day's level of nitrogen dioxide. No associations were found for sulphur dioxide or for ozone. CONCLUSIONS--This study provides further evidence of the effect of particulate pollution on asthma, and it suggests that nitrogen dioxide may have a role in the exacerbation of bronchial asthma in adults.
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