title: Association between Air Pollutants and Asthma Emergency Room Visits and Hospital Admissions in Time Series Studies: A Systematic Review and Meta-Analysis.
abstract: BACKGROUND
  Air pollution constitutes a significant stimulus of asthma exacerbations; however, the impacts of exposure to major air pollutants on asthma-related hospital admissions and emergency room visits (ERVs) have not been fully determined.
  
  
  OBJECTIVE
  We sought to quantify the associations between short-term exposure to air pollutants [ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter ≤10 μm (PM10) and PM2.5] and the asthma-related emergency room visits (ERV) and hospitalizations.
  
  
  METHODS
  Systematic computerized searches without language limitation were performed. Pooled relative risks (RRs) and 95% confidence intervals (95%CIs) were estimated using the random-effect models. Sensitivity analyses and subgroup analyses were also performed.
  
  
  RESULTS
  After screening of 246 studies, 87 were included in our analyses. Air pollutants were associated with significantly increased risks of asthma ERVs and hospitalizations [O3: RR(95%CI), 1.009 (1.006, 1.011); I2 = 87.8%, population-attributable fraction (PAF) (95%CI): 0.8 (0.6, 1.1); CO: RR(95%CI), 1.045 (1.029, 1.061); I2 = 85.7%, PAF (95%CI): 4.3 (2.8, 5.7); NO2: RR(95%CI), 1.018 (1.014, 1.022); I2 = 87.6%, PAF (95%CI): 1.8 (1.4, 2.2); SO2: RR(95%CI), 1.011 (1.007, 1.015); I2 = 77.1%, PAF (95%CI): 1.1 (0.7, 1.5); PM10: RR(95%CI), 1.010 (1.008, 1.013); I2 = 69.1%, PAF (95%CI): 1.1 (0.8, 1.3); PM2.5: RR(95%CI), 1.023 (1.015, 1.031); I2 = 82.8%, PAF (95%CI): 2.3 (1.5, 3.1)]. Sensitivity analyses yielded compatible findings as compared with the overall analyses without publication bias. Stronger associations were found in hospitalized males, children and elderly patients in warm seasons with lag of 2 days or greater.
  
  
  CONCLUSIONS
  Short-term exposures to air pollutants account for increased risks of asthma-related ERVs and hospitalizations that constitute a considerable healthcare utilization and socioeconomic burden.
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Xue-yan
authors.initials: XY
authors.lastname: Zheng
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Ding
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Li-na
authors.initials: LN
authors.lastname: Jiang
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Shao-wei
authors.initials: SW
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, Guangzhou Institute of Respiratory Disease, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou Medical University, Guangzhou, China.
authors.forename: Jin-ping
authors.initials: JP
authors.lastname: Zheng
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Min
authors.initials: M
authors.lastname: Qiu
authors.affiliation: Department of Biostatistics, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Ying-xue
authors.initials: YX
authors.lastname: Zhou
authors.affiliation: Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangdong, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, Guangzhou Institute of Respiratory Disease, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou Medical University, Guangzhou, China.
authors.forename: Wei-jie
authors.initials: WJ
authors.lastname: Guan
mesh_terms: D000368:Aged; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis; D000553:Ambulatory Care / Q000706:statistics & numerical data*; D001249:Asthma / Q000453:epidemiology* / Q000628:therapy; D002648:Child; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D052638:Particulate Matter / Q000032:analysis*; D010343:Patient Admission / Q000706:statistics & numerical data*; D012621:Seasons; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter