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Table 2 Other cohort studies

From: Does traffic exhaust contribute to the development of asthma and allergic sensitization in children: findings from recent cohort studies

Study Study population Age Exposure assessment Agent Range of exposure Outcome Relative risk Comments
Islam et al 2007 2,057 schoolchildren from 12 communities in southern California within CHS, Children's Health Study, were enrolled at 9–10 yrs of age and followed for up to 8 yrs   Community level NO2, PM2.5
and others
The levels of air pollutants were closely correlated (except for ozone)
8–75 μg/m3
5–29 μg/m3
Incidence of doctor-diagnosed asthma
Annual lung function measurements
A protective effect of a good lung function on the incidence of asthma was attenuated in communities with high levels of traffic related pollutants. Crude exposure assessment, mainly
dichotomous at community level.
Jerrett et al
2008
217 children from 11 communities in southern California within CHS were followed for eight yrs. 10 yrs at the entry of the study 2 × 2 weeks measurement outside the home of each child NO2 ~10 – 102 μg/m3 Self-reported incidence of physician diagnosed asthma Hazard ratio was 1.29 (1.07–1.56) across the average interquartile range of ≈ 12 μg/m3. Very small study size with only 26 new cases of asthma
Shima et al 2002 Prospective cohort study of 3,049 children in 8 different communities followed annually during the first six years at school 12 yrs Community level exposure assessment. NO2, PM10 Nearest monitoring station
NO2 14–62 μg/m3
PM10 28–54 μg/m3
10 year mean values
Annual questionnaires.
Asthma defined as recurrent wheeze and medication for asthma
OR for 48 μg/m3 increase of NO2 3.62 (1.11–11.87) for the cumulative incidence of asthma. Limitations: There may be uncontrolled confounding at a community level. In a way, a comparison between urban and rural areas
Shima et al
2003
Prospective cohort study of 2,506 schoolchildren in 8 different communities followed annually over 4 years   Community level exposure assessment and individual exposure regarding distance between home and road. NO2, Nearest monitoring station
NO2 14–62 μg/m3
Annual questionnaires
Asthma defined as recurrent wheeze and medication for asthma
OR close to 4 for the cumulative incidence of asthma when children from roadside areas were compared with rural children Crude exposure assessment.
Confounders may contribute to a lower incidence of asthma in rural areas