Table 2 Other 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 |