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Coarse and fine particles but not ultrafine particles in urban air trigger hospital admission for asthma in children
  1. Amne Iskandar1,
  2. Zorana Jovanovic Andersen2,
  3. Klaus Bønnelykke1,
  4. Thomas Ellermann3,
  5. Klaus Kaae Andersen2,
  6. Hans Bisgaard1
  1. 1Copenhagen Prospective Studies on Asthma in Childhood, Health Sciences, University of Copenhagen and Copenhagen University Hospital, Gentofte, Copenhagen, Denmark
  2. 2Danish Cancer Society, Institute of Cancer Epidemiology, Copenhagen, Denmark
  3. 3Aarhus University, National Environmental Research Institute, Roskilde, Denmark
  1. Correspondence to Professor Hans Bisgaard, Copenhagen Prospective Studies on Asthma in Childhood, Health Sciences, University of Copenhagen, Copenhagen University Hospital, Ledreborg Allé 34, 2820 Gentofte, Denmark; bisgaard{at}


Background Short-term exposure to air pollution can trigger hospital admissions for asthma in children, but it is not known which components of air pollution are most important. There are no available studies on the particular effect of ultrafine particles (UFPs) on paediatric admissions for asthma.

Aim To study whether short-term exposure to air pollution is associated with hospital admissions for asthma in children. It is hypothesised that (1) the association between asthma admissions and air pollution is stronger with UFPs than with coarse (PM10) and fine (PM2.5) particles, nitrogen oxides (NOx) or nitrogen dioxide (NO2); and (2) infants are more susceptible to the effects of exposure to air pollution than older children.

Method Daily counts of admissions for asthma in children aged 0–18 years to hospitals located within a 15 km radius of the central fixed background urban air pollution measurement station in Copenhagen between 2001 and 2008 were extracted from the Danish National Patient Registry. A time-stratified case crossover design was applied and data were analysed using conditional logistic regression to estimate the effect of air pollution on asthma admissions.

Results A significant association was found between hospital admissions for asthma in children aged 0–18 years and NOx (OR 1.11; 95% CI 1.05 to 1.17), NO2 (1.10; 95% CI 1.04 to 1.16), PM10 (1.07; 95% CI 1.03 to 1.12) and PM2.5 (1.09; 95% CI 1.04 to 1.13); there was no association with UFPs. The association was stronger in infants than in older children for all pollutants, but no statistically significant interaction was detected.

Conclusion Short-term exposure to air pollution can trigger hospital admission for asthma in children, with infants possibly being most susceptible. These effects seemed to be mediated by larger particles and traffic-related gases, whereas UFPs showed no effect.

  • Air pollution
  • hospitalisations
  • childhood asthma
  • case-crossover study
  • asthma
  • asthma epidemiology
  • paediatric asthma
  • COPD epidemiology
  • occupational lung disease
  • asthma guidelines
  • asthma mechanisms
  • asthma pharmacology
  • exhaled airway markers
  • inhaler devices
  • nebuliser therapy

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  • Funding COPSAC is funded by private and public research funds all listed on The Lundbeck Foundation, the Pharmacy Foundation of 1991, Augustinus Foundation, the Danish Medical Research Council and the Danish Paediatric Asthma Centre provided core support for COPSAC. Measurements of air pollution and meteorology have been funded by the Danish Environmental Protection Agency and via the Danish air quality monitoring programmes. The funding agencies did not have any role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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