Characteristics of the study population (n = 2936)
| Baseline n (%)* | Follow up n (%)* | |
|---|---|---|
| %, prevalence; SD, standard deviation; IQR, interquartile range; ETS, environmental tobacco smoke; NA, not applicable/assessed. | ||
| *Unless otherwise specified. | ||
| †Atopy is defined as either at least one positive skin prick test (wheal size ⩾3 mm after subtraction of negative control) or specific serum IgE levels >0.7 kU/l (a panel of common aeroallergens tested for both). | ||
| Mean (SD) age (years) | 9.6 (0.56) | 17.1 (0.62) |
| Sex | ||
| Female | 1592 (54.2) | 1592 (54.2) |
| Male | 1344 (45.8) | 1344 (45.8) |
| Symptoms and diagnosis of respiratory disease | ||
| Incident wheeze (yes) | NA | 388 (13.2) |
| Incident wheeze without a cold (yes) | NA | 158 (5.8) |
| Incidence of diagnosed asthma (yes) | NA | 66 (2.6) |
| Parental history of | ||
| Allergic disease (yes) | 1258 (43.2) | NA |
| Asthma (yes) | 241 (9.0) | NA |
| Clinical examination | ||
| Bronchial hyperreactivity (yes) | 186 (15.2) | NA |
| Atopy† (yes) | 780 (36.6) | NA |
| Median (IQR) plasma α1-antitrypsin (mg/dl) | 152.0 (25.0) | NA |
| Active smoking during adolescence (yes) | NA | 993 (34.1) |
| Mean (SD) age at onset of smoking (years) | NA | 14.1 (1.54) |
| Duration of active smoking | ||
| Never | NA | 1922 (66.4) |
| ⩽2 years | NA | 395 (13.6) |
| 2–4 years | NA | 422 (14.6) |
| >4 years | NA | 156 (5.4) |
| Mean (SD) duration of active smoking (years) | NA | 2.6 (1.35) |
| Intensity of active smoking | ||
| Never | NA | 1922 (66.1) |
| Occasionally | NA | 169 (5.8) |
| Daily ⩽10 cigarettes | NA | 440 (15.1) |
| Daily >10 cigarettes | NA | 378 (13.0) |
| Exposure to ETS (yes) | 1094 (38.9) | 1863 (63.9) |
| Exposure to ETS at home (yes) | 1094 (38.9) | 920 (40.2) |
| Duration of ETS exposure | ||
| Never | NA | 997 (34.4) |
| ⩽1 h/day | NA | 560 (19.3) |
| 1–5 h/day | NA | 863 (29.8) |
| >5 h/day | NA | 478 (16.5) |