title: Air pollution is associated with primary health care visits for asthma in Sweden: A case-crossover design with a distributed lag non-linear model.
abstract: Air pollution can increase the symptoms of asthma and has an acute effect on the number of emergency room visits and hospital admissions because of asthma, but little is known about the effect of air pollution on the number of primary health care (PHC) visits for asthma.
  
  
  
  To investigate the association between air pollution and the number of PHC visits for asthma in Scania, southern Sweden.
  
  
  
  Data on daily PHC visits for asthma were obtained from a regional healthcare database in Scania, which covers approximately half a million people. Air pollution data from 2005 to 2010 were obtained from six urban background stations. We used a case-crossover study design and a distributed lag non-linear model in the analysis.
  
  
  
  The air pollution levels were generally within the EU air quality guidelines. The mean number of daily PHC visits for asthma was 34. The number of PHC visits increased by 5% (95% confidence interval (CI): 3.91-6.25%) with every 10µg m(-3) increase in daily mean NO2 lag (0-15), suggesting that daily air pollution levels are associated with PHC visits for asthma.
  
  
  
  Even though the air quality in Scania between 2005 and 2010 was within EU's guidelines, the number of PHC visits for asthma increased with increasing levels of air pollution. This suggests that as well as increasing hospital and emergency room visits, air pollution increases the burden on PHC due to milder symptoms of asthma.
authors.affiliation: Laboratory Medicine, Occupational and Environmental Medicine, Lund University, Lund, Sweden. . Electronic address: tahir.taj@med.lu.se.
authors.forename: Tahir
authors.initials: T
authors.lastname: Taj
authors.affiliation: Laboratory Medicine, Occupational and Environmental Medicine, Lund University, Lund, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Jakobsson
authors.affiliation: Laboratory Medicine, Occupational and Environmental Medicine, Lund University, Lund, Sweden. ; Occupational and Environmental Medicine, Umeå University, 90187 Umeå, Sweden.
authors.forename: Emilie
authors.initials: E
authors.lastname: Stroh
authors.affiliation: Occupational and Environmental Medicine, Umeå University, 90187 Umeå, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Oudin
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D000397:Air Pollution / Q000706:statistics & numerical data*; D001249:Asthma / Q000453:epidemiology*; D018592:Cross-Over Studies; D006801:Humans; D017711:Nonlinear Dynamics; D009819:Office Visits / Q000706:statistics & numerical data*; D011320:Primary Health Care / Q000706:statistics & numerical data*; D013548:Sweden / Q000453:epidemiology; D014505:Urban Population
chemical_list: D000393:Air Pollutants
keywords: Air pollution; Asthma; Primary Health Care