Effects of Coarse Particulate Matter on Emergency Hospital Admissions for Respiratory Diseases: A Time-Series Analysis in Hong Kong

BACKGROUND: Many epidemiological studies have linked daily counts of hospital admissions to particulate matter (PM) with an aerodynamic diameter <= 10 mu m (PM10) and <= 2.5 mu m (PM2.5), but relatively few have investigated the relationship of hospital admissions with coarse PM (PMc; 2.5-10 mu m aerodynamic diameter). OBJECTIVES: We conducted this study to estimate the health effects of PMc on emergency hospital admissions for respiratory diseases in Hong Kong after controlling for PM2.5 and gaseous pollutants. METHODS: We conducted a time-series analysis of associations between daily emergency hospital admissions for respiratory diseases in Hong Kong from January 2000 to December 2005 and daily PM2.5 and PMc concentrations. We estimated PMc concentrations by subtracting PM2.5 from PM10 measurements. We used generalized additive models to examine the relationship between PMc (single-and multiday lagged exposures) and hospital admissions adjusted for time trends, weather conditions, influenza outbreaks, PM2.5, and gaseous pollutants (nitrogen dioxide, sulfur dioxide, and ozone). RESULTS: A 10.9-mu g/m(3) (interquartile range) increase in the 4-day moving average concentration of PMc was associated with a 1.94% (95% confidence interval: 1.24%, 2.64%) increase in emergency hospital admissions for respiratory diseases that was attenuated but still significant after controlling for PM2.5. Adjusting for gaseous pollutants and altering models assumptions had little influence on PMc effect estimates. CONCLUSION: PMc was associated with emergency hospital admissions for respiratory diseases in Hong Kong independent of PM2.5 and gaseous pollutants. Further research is needed to evaluate health effects of different components of PMc.