Comparison of the Effects of Air Pollution on Outpatient and Inpatient Visits for Asthma: A Population-Based Study in Taiwan

BACKGROUND A nationwide asthma survey on the effects of air pollution is lacking in Taiwan. The purpose of this study was to evaluate the time trend and the relationship between air pollution and health care services for asthma in Taiwan. METHODS Health care services for asthma and ambient air pollution data were obtained from the National Health Insurance Research database and Environmental Protection Administration from 2000 through 2009, respectively. Health care services, including those related to the outpatient and inpatient visits were compared according to the concentration of air pollutants. RESULTS The number of asthma-patient visits to health-care facilities continue to increase in Taiwan. Relative to the respective lowest quartile of air pollutants, the adjusted relative risks (RRs) of the outpatient visits in the highest quartile were 1.10 (P-trend  = 0.013) for carbon monoxide (CO), 1.10 (P-trend  = 0.015) for nitrogen dioxide (NO2), and 1.20 (P-trend <0.0001) for particulate matter with an aerodynamic diameter ≦ 10 µm (PM10) in the child group (aged 0-18). For adults aged 19-44, the RRs of outpatient visits were 1.13 (P-trend = 0.078) for CO, 1.17 (P-trend = 0.002) for NO2, and 1.13 (P-trend <0.0001) for PM10. For adults aged 45-64, the RRs of outpatient visits were 1.15 (P-trend = 0.003) for CO, 1.19 (P-trend = 0.0002) for NO2, and 1.10 (P-trend = 0.001) for PM10. For the elderly (aged ≥ 65), the RRs of outpatient visits in were 1.12 (P-trend  = 0.003) for NO2 and 1.10 (P-trend  = 0.006) for PM10. For inpatient visits, the RRs across quartiles of CO level were 1.00, 1.70, 1.92, and 1.86 (P-trend  = 0.0001) in the child group. There were no significant linear associations between inpatient visits and air pollutants in other groups. CONCLUSIONS There were positive associations between CO levels and childhood inpatient visits as well as NO2, CO and PM10 and outpatient visits.