| Swimming infants | Controls | p-value | |
| Subjects n | 195 | 235 | |
| Males | 105 (53.9) | 124 (52.8) | 0.82 |
| School participation rate % | 54.9±19.4 | 58. 3±23.0 | 0.19 |
| Age yrs | 5.60±0.38 | 5.68±0.38 | 0.79 |
| BMI kg·m-2 | 20.9±3.8 | 20.6±3.5 | 0.39 |
| Parents | |||
| Higher educational level | 154 (79.0) | 156 (66.4) | 0.004 |
| Asthma | 38 (19.5) | 25 (10.6) | 0.01 |
| Asthma and/or respiratory allergies | 86 (44.1) | 88 (37.4) | 0.16 |
| Early life | |||
| Birthweight g | 3206±639 | 3436±2396 | 0.30 |
| Breastfeeding | 161 (82.6) | 169 (71.9) | 0.01 |
| Day-care centre attendance | 127 (65.1) | 102 (43.4) | <0.001 |
| Exposure to tobacco smoke | |||
| During pregnancy | 31 (16.0) | 32 (13.6) | 0.51 |
| Parental smoking at home | 55 (28.2) | 74 (31.5) | 0.46 |
| CPA before age of 2 yrs h | |||
| Indoor | 6 (0–21) | ||
| Outdoor | 8 (0–31) | ||
| Total | 22 (8–50) | ||
| CPA over lifetime h | |||
| Indoor | 53 (17–129) | 18 (0–48) | <0.001 |
| Outdoor | 50 (4–146) | 0 (0–28) | <0.001 |
| Total | 132 (52–202) | 35 (5–91) | <0.001 |
| Environment and lifestyle | |||
| Number of older siblings | 0.87±0.79 | 0.92±1.12 | 0.66 |
| House cleaning with bleach | 43 (22.1) | 66 (28.1) | 0.15 |
| Living <100 m from a busy road | 63 (32.3) | 79 (33.6) | 0.78 |
| Exposure to pets since birth | 85 (43.6) | 99 (42.1) | 0.76 |
| Aeroallergen-specific nasal IgE# | |||
| House dust mite | 21 (12.2) | 22 (11.0) | 0.71 |
| Cat | 15 (8.7) | 14 (7.0) | 0.54 |
| Pollen | 27 (15.7) | 27 (13.5) | 0.55 |
| At least one aeroallergen | 42 (24.4) | 48 (24.0) | 0.92 |
| Respiratory symptoms and diseases¶ | |||
| Wheezing+ | 36 (18.5) | 40 (17.0) | 0.70 |
| Asthma | 16 (8.2) | 15 (6.4) | 0.47 |
| Hay fever | 17 (8.7) | 27 (11.5) | 0.35 |
| Allergic rhinitis | 27 (13.9) | 25 (10.6) | 0.31 |
| Bronchiolitis | 71 (36.4) | 56 (23.8) | 0.004 |
| Bronchitis | 93 (47.7) | 111 (47.2) | 0.92 |
| Sinusitis | 28 (14.4) | 30 (12.8) | 0.63 |
| Pneumonia | 20 (10.3) | 28 (11.9) | 0.59 |
Data are presented as mean±sd, n (%) or median (interquartile range) unless otherwise indicated. BMI: body mass index; CPA: cumulative pool attendance; Ig: immunoglobulin. #: 172 children were tested in the swimming infant group and 200 in the other group; ¶: defined as doctor-diagnosed diseases at any time; +: episodes of wheezing during the last 12 months.