Effects of air pollution on asthma hospitalization rates in different age groups in Hong Kong

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Abstract
Aims To assess the relationship between levels of ambient air pollutants and hospitalization rates for asthma in Hong Kong (HK). Methods This is a retrospective ecological study. Data of daily emergency hospital admissions to 15 major hospitals in HK for asthma and indices of air pollutants [sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), particulates with an aerodynamic diameter of 10) and 2.5 μm (PM2.5)] and meteorological variables from January 2000 to December 2005 were obtained from several government departments. Analysis was performed by the generalized additive models with Poisson distribution. The effects of time trend, season, other cyclical factors, temperature and humidity were adjusted. Autocorrelation and overdispersion were corrected. Results Altogether, 69 716 admissions were assessed. Significant associations were found between hospital admissions for asthma and levels of NO2, O3, PM10 and PM2.5. The relative risks (RR) for hospitalization for every 10 μg/m3 increase in NO2, O3, PM10 and PM2.5 were 1.028, 1.034, 1.019 and 1.021, respectively, at a lag day that ranged from cumulative lag 0–4 to 0–5. In a multi-pollutant model, O3 was significantly associated with increased admissions for asthma. The younger age group (0–14 years) tended to have a higher RR for each 10 μg/m3 increase in pollutants than those aged 15–65 years. The elderly (aged 65 years) had a shorter ‘best’ lag time to develop asthma exacerbation following exposure to pollutants than those aged <65 years. Conclusion Adverse effects of ambient concentrations of air pollutants on hospitalization rates for asthma are evident. Measures to improve air quality in HK are urgently needed.