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

Date Published: May 1, 2014

Publisher: Public Library of Science

Author(s): Hui-Hsien Pan, Chun-Tzu Chen, Hai-Lun Sun, Min-Sho Ku, Pei-Fen Liao, Ko-Hsiu Lu, Ji-Nan Sheu, Jing-Yang Huang, Jar-Yuan Pai, Ko-Huang Lue, Stephania Ann Cormier.


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.

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.

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 ≦10µm (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. There were positive associations between CO levels and childhood inpatient visits as well as NO2, CO and PM10 and outpatient visits.

Partial Text

Asthma is a common chronic inflammatory respiratory disease that affects 300 million people of all ages and all ethnic backgrounds and accounts for about 1 in every 250 deaths worldwide [1]. In Taiwan, the prevalence of asthma increased from 5.07% in 1985 to 11.9% in 2007 [2], [3]. The risk factors for asthma include many external determinants such as mites, dust, mold, indoor and outdoor air pollution, and season variations [4]–[6]. Although air pollution has not been shown as the sole cause of respiratory illnesses, there is evidence that air pollution episodes lead to respiratory irritation, increased use of asthma medications and hospitalizations [7], [8]. Traffic and industry-related pollutants, nitrogen dioxide (NO2) and carbon monoxide (CO), were associated with asthma hospitalizations and outpatient visits [9], [10]. Elevated levels of ozone (O3), sulfur dioxide (SO2) and particulate matter with an aerodynamic diameter ≦10µm (PM10) were reported to be related with increased asthma emergency room visits and admissions [11]–[13]. It has been reported that the rise in air pollution has increased respiratory and cardiovascular complications leading to elevated risk of death [14].

The descriptive statistics for outpatient and inpatient visits and corresponding period and season data are shown in Table 1. Compared with women, the RRs for inpatient and outpatient visits in men were 1.31 (p<0.0001) and 1.15 (p<0.0001), respectively. Furthermore, when divided into 4 age groups, the highest RRs for inpatient and outpatient visits were among the elderly group (i.e. ≥65 years) followed by the child group (0 –18), the adults aged 45–64 group and the adult aged 19–44 group. For the period effect, there were increased outpatient visits (RR: 1.29, P<0.0001) since 2005 and inpatient visits (RR: 3.30, P<0.0001) since 2006 when compared with patient visits in 2000. The peak seasons for asthma inpatient and outpatient visits in Taiwan were spring (5.1/10,000 person-season) and winter (149.6/10,000 person-season), respectively. Among patients with asthma, air pollutant exposure causes increased asthma morbidity. Little is known about changes over time in air pollutant exposure among patients with asthma in a national sample. During the study period, the inpatient and outpatient visits by men were higher than in women. The peak seasons of asthma inpatient and outpatient visits for the total population were spring and winter, respectively. The inpatient and outpatient visits of asthmatics have not reached a plateau and have continued to increase. Inpatient visits for asthma increased with increased levels of CO in children but not for any pollutants in adults in the present study. Our study found that CO, NO2 and PM10 had significant estimated associations on outpatient visits due to asthma and children are more susceptible than other age groups.   Source: