| CPA category | CPA h | Subjects n/N (%) | OR (95% CI) | p-value | ptrend | |
| Unadjusted | Adjusted | |||||
| Indoor pool total¶ | ||||||
| 0 h | 0 | 76/287 (26.5) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||
| >0–20 h | 6 (2–12) | 27/92 (29.4) | 1.15 (0.69–1.94) | 0.79 (0.44–1.42) | 0.44 | |
| >20 h | 32 (25–45) | 24/51 (47.1) | 2.47 (1.34–4.54) | 2.02 (1.01–4.02) | 0.05 | 0.006 |
| Outdoor pool total¶ | ||||||
| 0 h | 0 | 79/308 (25.7) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||
| >0–20 h | 9 (5–14) | 21/54 (38.9) | 1.85 (1.01–3.38) | 1.91 (0.99–3.68) | 0.05 | |
| >20 h | 47 (30–84) | 27/68 (39.7) | 1.91 (1.1–3.3) | 1.59 (0.85–2.98) | 0.14 | 0.006 |
| Indoor pool alone | ||||||
| 0 h | 0 | 53/235 (22.6) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||
| >0–20 h | 6 (2–11) | 11/50 (22.0) | 0.9 (0.43–1.88) | 0.58 (0.25–1.32) | 0.19 | |
| >20 h | 36 (24–66) | 12/23 (52.2) | 3.49 (1.46–8.34) | 3.49 (1.30–9.34) | 0.01 | 0.01 |
| Outdoor pool alone | ||||||
| 0 h | 0 | 59/235 (25.1) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||
| >0–20 h | 9 (4–12) | 9/27 (33.3) | 1.6 (0.68–3.76) | 1.69 (0.66–4.3) | 0.27 | |
| >20 h | 50 (39–76) | 11/25 (44.0) | 2.51 (1.08–5.85 | 2.08 (0.81–5.34) | 0.13 | 0.03 |
CPA is presented as median (interquartile range). Odds ratios (ORs) were adjusted for sex, breastfeeding, day-care centre attendance, number of older siblings, parental asthma and/or respiratory allergies, maternal smoking during pregnancy, and, when the analysis was performed on all children, attendance of the other type of swimming. CI: confidence interval; N: number of subjects in group; ptrend: p-value for trend. #: before the age of 2 yrs; ¶: all children.