Prevalence of potential risk factors in childhood among never-asthma and ever-asthma, and by different age at asthma onset
| Never-asthma (n=2740) | Ever-asthma (n=690) | p-value# | Age at asthma onset | p-value¶ | ||||
| ≤8 years (n=248) | 9–13 years (n=169) | 14–19 years (n=184) | >19 years (n=89) | |||||
| Female sex | 1330 (48.6) | 349 (50.6) | 0.338 | 105 (42.3) | 78 (46.2) | 116 (56.2) | 50 (56.2) | <0.001 |
| Family history of asthma | 470 (17.2) | 252 (36.5) | <0.001 | 109 (44.0) | 69 (40.8) | 50 (27.2) | 24 (27.0) | <0.001 |
| Low birthweight | 98 (3.7) | 41 (6.2) | 0.004 | 18 (7.6) | 8 (4.9) | 8 (4.5) | 7 (8.0) | 0.019 |
| Breastfeeding <3 months | 639 (24.0) | 207 (31.2) | <0.001 | 88 (36.7) | 28 (17.2) | 59 (33.5) | 32 (37.6) | <0.001 |
| Any severe respiratory infection before age 8 years | 1507 (55.0) | 451 (65.4) | <0.001 | 191 (77.0) | 103 (60.9) | 107 (58.2) | 50 (56.2) | <0.001 |
| Smoking during pregnancy | 646 (24.0) | 196 (29.3) | 0.005 | 74 (30.2) | 47 (29.0) | 55 (30.9) | 20 (23.5) | 0.043 |
| Exposure to maternal smoking in first 2 years of life | 816 (31.1) | 228 (34.8) | 0.075 | 85 (35.7) | 53 (33.3) | 64 (36.6) | 26 (31.0) | 0.374 |
| Exposure to maternal smoking at age 8 years | 809 (30.3) | 241 (36.2) | 0.003 | 94 (39.3) | 58 (35.8) | 59 (33.0) | 30 (35.3) | 0.030 |
Data are presented as n (%), unless otherwise stated. Missing values in individual variables: low birthweight n=124, breastfeeding n=104, smoking during pregnancy n=65, exposure to maternal smoking in first 2 years n=94 and exposure to maternal smoking at age 8 years n=153. #: difference between never-asthma and ever-asthma analysed by the Chi-squared test. ¶: difference between never-asthma and all asthma onset groups analysed by the Chi-squared test.