Association of ambient air-pollution levels with acute asthma exacerbation among children in Singapore

Background: Air-pollution levels have been shown to be associated with increased morbidity of respiratory diseases. Methods: Data for ambient air-pollutant levels, meteorologic factors, and hospitalization or emergency room (ER) visits for acute asthma in Singapore children over a 5-year period (1990-4) were obtained and analyzed for associations by time-series methods. Results: Throughout this period, the annual mean and 24-h mean levels for sulfur dioxide (SO2), nitrogen dioxide (NO2), and total suspended particles (TSP) and maximum 1-h daily average for ozone were generally within the air-quality guidelines established by the World Health Organization (WHO). However, positive correlation between levels of each of these pollutants and daily ER visits for asthma was observed in children aged 3-12 years, but not among adolescents and young adults (13-21 years old). The association with SO2 and TSP persisted after standardization for meteorologic and temporal variables. An adjusted increase in 2.9 ER visits for every 20 mu g/m(3) increase in atmospheric SO2 levels, lagged by 1 day, was observed on days when levels were above 68 mu g/m(3). With TSP, an adjusted increase of 5.80 ER visits for every 20 mu g/m(3) increase in its daily atmospheric levels, lagged by 1 day, was observed on days with levels above 73 mu g/m(3). Similar results were also obtained after controlling for autocorrelation by time-series analysis. Conclusions: These associations were observed even though the overall levels of all pollutants were generally within the air-quality guidelines established by the WHO. These findings suggest that asthmatic children are susceptible to increased levels of air pollutants, particularly SO2 and TSP, although the ambient levels are generally within "acceptable" ranges.