title: Spatial analysis of air pollution and childhood asthma in Hamilton, Canada: comparing exposure methods in sensitive subgroups.
abstract: BACKGROUND
  Variations in air pollution exposure within a community may be associated with asthma prevalence. However, studies conducted to date have produced inconsistent results, possibly due to errors in measurement of the exposures.
  
  
  METHODS
  A standardized asthma survey was administered to children in grades one and eight in Hamilton, Canada, in 1994-95 (N approximately 1467). Exposure to air pollution was estimated in four ways: (1) distance from roadways; (2) interpolated surfaces for ozone, sulfur dioxide, particulate matter and nitrous oxides from seven to nine governmental monitoring stations; (3) a kriged nitrogen dioxide (NO2) surface based on a network of 100 passive NO2 monitors; and (4) a land use regression (LUR) model derived from the same monitoring network. Logistic regressions were used to test associations between asthma and air pollution, controlling for variables including neighbourhood income, dwelling value, state of housing, a deprivation index and smoking.
  
  
  RESULTS
  There were no significant associations between any of the exposure estimates and asthma in the whole population, but large effects were detected the subgroup of children without hayfever (predominately in girls). The most robust effects were observed for the association of asthma without hayfever and NO2LUR OR = 1.86 (95%CI, 1.59-2.16) in all girls and OR = 2.98 (95%CI, 0.98-9.06) for older girls, over an interquartile range increase and controlling for confounders.
  
  
  CONCLUSIONS
  Our findings indicate that traffic-related pollutants, such as NO2, are associated with asthma without overt evidence of other atopic disorders among female children living in a medium-sized Canadian city. The effects were sensitive to the method of exposure estimation. More refined exposure models produced the most robust associations.
authors.affiliation: School of Geography and Earth Sciences, 1280 King St West, Hamilton, L8S 4K1, Canada. talars@gmail.com
authors.forename: Talar
authors.initials: T
authors.lastname: Sahsuvaroglu
authors.forename: Michael
authors.initials: M
authors.lastname: Jerrett
authors.forename: Malcolm R
authors.initials: MR
authors.lastname: Sears
authors.forename: Rob
authors.initials: R
authors.lastname: McConnell
authors.forename: Norm
authors.initials: N
authors.lastname: Finkelstein
authors.forename: Altaf
authors.initials: A
authors.lastname: Arain
authors.forename: Bruce
authors.initials: B
authors.lastname: Newbold
authors.forename: Rick
authors.initials: R
authors.lastname: Burnett