Association between prevalence of asthma and wheezing at the age of 1½ years and outdoor NOx or EC concentrations in the baseline survey using a logistic model, adjusted for potential confounding variables (n=57 682)*†
| Outcomes | ||
|---|---|---|
| Prevalence of asthma | Prevalence of wheezing | |
| Outdoor NOx concentration | ||
| Level 5 (50.9–136.8 ppb) | 1.20 (0.79 to 1.84) | 1.08 (0.97 to 1.21) |
| Level 4 (42.1–50.8 ppb) | 1.08 (0.80 to 1.45) | 1.05 (0.98 to 1.14) |
| Level 3 (37.2–42.0 ppb) | 0.92 (0.70 to 1.22) | 1.05 (0.98 to 1.12) |
| Level 2 (32.6–37.1 ppb) | 1.18 (0.91 to 1.52) | 1.06 (0.99 to 1.13) |
| Level 1 (13.9–32.5 ppb) | 1.00 | 1.00 |
| Outdoor EC concentration | ||
| Level 5 (3.6–7.5 μg/m3) | 1.04 (0.79 to 1.84) | 1.08 (0.97 to 1.21) |
| Level 4 (3.1–3.5 μg/m3) | 1.02 (0.80 to 1.45) | 1.10 (1.01 to 1.19) |
| Level 3 (2.8–3.0 μg/m3) | 1.01 (0.70 to 1.22) | 1.10 (1.02 to 1.18) |
| Level 2 (2.5–2.7 μg/m3) | 0.93 (0.91 to 1.52) | 1.10 (1.03 to 1.18) |
| Level 1 (1.3–2.4 μg/m3) | 1.00 | 1.00 |
| Continuous variables for outdoor concentration | ||
| NOx (per 1 ppb) | 1.00 (0.99 to 1.01) | 1.00 (1.00 to 1.01) |
| EC (per 0.1 μg/m3) | 1.01 (0.98 to 1.03) | 1.01 (1.00 to 1.01) |
*Data are presented as OR (95% CIs).
†Potential confounding variables include gender, districts, birth season, years of residence, feeding method during the first 3 months of life, familial smoking habits, structure of house, heating system, keeping pets (cats, birds, dogs, hamsters, others), background concentration of air pollutants, history of disease before the age of 1½ years, such as bronchitis/pneumonia, empyema and allergic disease; and parental history of allergic diseases, such as asthma, atopic dermatitis and pollinosis.
EC, elemental carbon; NOx, nitrogen oxides.