Table 2 |
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Other cohort studies |
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Study |
Study population |
Age |
Exposure assessment |
Agent |
Range of exposure |
Outcome |
Relative risk |
Comments |
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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. |
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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 |
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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 |
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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 |
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Bråbäck and Forsberg Environmental Health 2009 8:17 doi:10.1186/1476-069X-8-17 |
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