Risks of ever or current asthma and of elevated exhaled nitric oxide in adolescents according to their lifetime attendance of an outdoor chlorinated swimming pool at home(residential) or during the holidays (nonresidential)
| Indicator | Outdoor pool attendance h | Residential outdoor chlorinated pool | Nonresidential outdoor chlorinated pool | ||||||
| Crude OR (95% CI) | p-value | Adjusted OR (95% CI) | p-value | Crude OR (95% CI) | p-value | Adjusted OR (95% CI) | p-value | ||
| Ever asthma# | 0 | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||||
| >0–100 | 0.52 (0.16–1.72) | 0.29 | 0.43 (0.12–1.51) | 0.19 | 0.68 (0.34–1.36) | 0.28 | 0.60 (0.29–1.23) | 0.16 | |
| >100–500 | 1.11 (0.49–2.53) | 0.80 | 1.30 (0.56–3.07) | 0.54 | 1.29 (0.76–2.20) | 0.35 | 1.17 (0.67–2.05) | 0.59 | |
| >500 | 2.37 (1.05–5.37) | 0.04 | 2.44 (1.01–5.90) | 0.05 | 2.28 (1.14–4.54) | 0.02 | 2.09 (0.99–4.41) | 0.05 | |
| Current asthma¶ | 0 | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||||
| >0–100 | 0.28 (0.04–2.06) | 0.21 | 0.24 (0.03–1.86) | 0.17 | 0.97 (0.44–2.15) | 0.94 | 0.81 (0.35–1.92) | 0.64 | |
| >100–500 | 1.00 (0.35–2.88) | 1.00 | 1.26 (0.42–3.73) | 0.68 | 1.40 (0.72–2.70) | 0.32 | 1.19 (0.59–2.42) | 0.62 | |
| >500 | 2.76 (1.10–6.96) | 0.03 | 2.50 (0.88–7.12) | 0.09 | 1.96 (0.80–4.75) | 0.14 | 1.67 (0.64–4.36) | 0.29 | |
| Exhaled NO>30 ppb+ | 0 | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | 1.0 (1.0–1.0) | ||||
| >0–100 | 1.44 (0.70–2.97) | 0.38 | 1.37 (0.66–3.02) | 0.42 | 1.04 (0.62–1.74) | 0.88 | 0.96 (0.55–1.65) | 0.87 | |
| >100–500 | 0.54 (0.21–1.37) | 0.19 | 0.54 (0.20–1.38) | 0.21 | 1.02 (0.64–1.64) | 0.98 | 0.94 (0.57–1.56) | 0.82 | |
| >500 | 2.87 (1.40–5.87) | 0.004 | 2.88 (1.35–6.12) | 0.006 | 1.19 (0.59–2.40) | 0.99 | 0.99 (0.47–2.09) | 0.98 | |
#: odds ratios (ORs) for ever asthma were adjusted for total serum immunoglobulin (Ig)E, parental asthma, sex, maternal smoking during pregnancy, house cleaning with bleach, the presence of mould on bedroom walls, the number of older siblings and the attendance at the other type of outdoor pool. ¶: ORs for current asthma were adjusted for total serum IgE, parental asthma, sex, maternal smoking during pregnancy, house cleaning with bleach and the attendance at the other type of outdoor pool. +: ORs for exhaled nitric oxide were adjusted for total serum IgE, parental allergy, sex and house cleaning with bleach. The numbers of subjects among the referents and the three pool attendance categories were as follows. Residential pools: 692, 54, 63 and 38; nonresidential pools: 408, 164, 208 and 67.