title: Coarse and fine particles but not ultrafine particles in urban air trigger hospital admission for asthma in children.
abstract: 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.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Copenhagen Prospective Studies on Asthma in Childhood, Health Sciences, University of Copenhagen, Copenhagen University Hospital, Ledreborg Allé 34, 2820 Gentofte, Denmark.
authors.forename: Amne
authors.initials: A
authors.lastname: Iskandar
authors.forename: Zorana Jovanovic
authors.initials: ZJ
authors.lastname: Andersen
authors.forename: Klaus
authors.initials: K
authors.lastname: Bønnelykke
authors.forename: Thomas
authors.initials: T
authors.lastname: Ellermann
authors.forename: Klaus Kaae
authors.initials: KK
authors.lastname: Andersen
authors.forename: Hans
authors.initials: H
authors.lastname: Bisgaard
mesh_terms: D000293:Adolescent; D000367:Age Factors; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D002648:Child; D002675:Child, Preschool; D018592:Cross-Over Studies; D003718:Denmark / Q000453:epidemiology; D004784:Environmental Monitoring / Q000379:methods; D062665:Epidemiological Monitoring; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009585:Nitrogen Dioxide / Q000009:adverse effects / Q000032:analysis; D009589:Nitrogen Oxides / Q000009:adverse effects / Q000032:analysis; D010316:Particle Size; D052638:Particulate Matter / Q000009:adverse effects* / Q000032:analysis; D012737:Sex Factors; D014504:Urban Health / Q000706:statistics & numerical data
chemical_list: D009589:Nitrogen Oxides; D052638:Particulate Matter; D009585:Nitrogen Dioxide