title: Short-Term Fluctuations in Air Pollution and Asthma in Scania, Sweden. Is the Association Modified by Long-Term Concentrations?
abstract: OBJECTIVE
  Asthma is one of the most common respiratory diseases in the world. Research has shown that temporal increases in air pollution concentrations can aggravate asthma symptoms. The aim of this study was to assess whether individuals living in areas with higher air pollution concentrations responded differently to short-term temporal exposure to air pollution than those living in lower air pollution areas.
  
  
  METHODS
  The study was designed as a case-crossover study in Scania, Sweden. Outcome data was visits to primary health care clinics with asthma as the main complaint during the years 2007 to 2010. Nitrogen dioxide levels were obtained from 21 different air pollution monitoring stations. Short-term exposure was defined as the average concentration four days prior to the visit. Data was pooled for areas above and below a two-year average NO2 concentration of 10 μg/m3, dispersion modelled with an emission database.
  
  
  RESULTS
  The short-term association between NO2 and asthma visits seemed stronger in areas with NO2 levels below 10 μg/m3, with an odds ratio (OR) of 1.15 (95% confidence interval (CI): 1.08-1.23) associated with a 10 μg/m3 increase in NO2 compared to areas above 10 μg/m3 NO2 levels, where corresponding OR of 1.09 (95% CI: 1.02-1.17). However, this difference was not statistically significant. (p = 0.13).
  
  
  CONCLUSIONS
  The study provided some evidence, although not statistically significant, that short-term associations between air pollution and asthma may depend on background air pollution levels. However, we cannot rule out that the association is due to other spatially dependent factors in Scania. The study should be reproduced in other study areas.
authors.affiliation: Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden.
authors.forename: Tahir
authors.identifier: http://orcid.org/0000-0001-9320-9759
authors.initials: T
authors.lastname: Taj
authors.affiliation: Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden.
authors.forename: Emilie
authors.initials: E
authors.lastname: Stroh
authors.affiliation: Centre for Primary Health Care Research, Department of Clinical Science, Malmö, Lund University, Lund, Sweden.|Department of Occupational and Environmental Medicine, Umeå University, Umeå, Sweden.
authors.forename: Daniel Oudin
authors.initials: DO
authors.lastname: Åström
authors.affiliation: Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Jakobsson
authors.affiliation: Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden.|Department of Occupational and Environmental Medicine, Umeå University, Umeå, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Oudin
mesh_terms: D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000009:adverse effects* / Q000032:analysis; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology*; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D005843:Geography; D006801:Humans; D008297:Male; D008875:Middle Aged; D009585:Nitrogen Dioxide / Q000009:adverse effects; D016017:Odds Ratio; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D009585:Nitrogen Dioxide