title: Association between traffic-related air pollution and asthma in preschool children in a national Japanese nested case-control study.
abstract: OBJECTIVE
  There has been little study on the effect of traffic-related air pollution on the incidence and persistence of asthma in preschool children. We evaluated the association of exposure to traffic-related air pollution with the incidence/persistence of asthma during the first 3 years of life using a population-based study.
  
  
  METHODS
  A baseline survey was conducted in 1½-year-old children (n=63,266). A follow-up survey at 3 years of age (n=43,343) identified new-onset asthma cases (n=853) and persistence of asthma (n=214). In the prevalence/persistence study, the outdoor concentrations of nitrogen oxides (NOx) and elemental carbon (EC) at home during the first 1½ years of life were estimated by a dispersion model. In the nested case-control study, which regarded incidence of asthma as cases, the personal exposure levels were estimated by dispersion model including time-activity pattern.
  
  
  RESULTS
  There was no statistically significant association between the incidence of asthma between age 1½ and 3 years and personal exposure levels to NOx nor EC. However, the persistence of asthmatic symptoms (between 1½ and 3  ears) was significantly associated with outdoor concentrations of NOx. ORs for the persistence of asthmatic symptoms were 6.02 (95% CI 1.51 to 23.92) for the comparison between the upper 5th and lower 25th centiles of NOx.
  
  
  CONCLUSIONS
  While no statistically significant association was observed for the incidence of asthma, the persistence of asthmatic symptoms in preschool children was significantly associated with traffic-related air pollution. This supports its importance as a risk factor in childhood airway disease.
authors.affiliation: Department of Public Health, Hyogo College of Medicine, Nishinomiya, Japan Center for Environmental Information Science, Tokyo, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Hasunuma
authors.affiliation: Department of Biostatistics, Kyoto University School of Public Health, Kyoto, Japan.
authors.forename: Tosiya
authors.initials: T
authors.lastname: Sato
authors.affiliation: Department of Education for Childcare, Tokyo Kasei University, Tokyo, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Iwata
authors.affiliation: Department of Pediatrics, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Kohno
authors.affiliation: National Institute for Environmental Studies, Tsukuba, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nitta
authors.affiliation: National Hospital Organization Fukuoka Hospital, Fukuoka, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Odajima
authors.affiliation: National Institute for Environmental Studies, Tsukuba, Japan.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Ohara
authors.affiliation: Center Administration Division, Center for Clinical Research, Kobe University Hospital, Kobe, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Omori
authors.affiliation: National Institute for Environmental Studies, Tsukuba, Japan.
authors.forename: Masaji
authors.initials: M
authors.lastname: Ono
authors.affiliation: National Institute for Environmental Studies, Tsukuba, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Yamazaki
authors.affiliation: Department of Public Health, Hyogo College of Medicine, Nishinomiya, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Shima
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects*; D000397:Air Pollution / Q000009:adverse effects*; D001249:Asthma / Q000453:epidemiology*; D016022:Case-Control Studies; D002675:Child, Preschool; D004784:Environmental Monitoring / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D012307:Risk Factors; D001335:Vehicle Emissions
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions
keywords: Air pollution; Automobile exhaust; EPIDEMIOLOGY; Preschool children