Table 3– Risk of bronchiolitis with increasing cumulative pool attendance (CPA) at indoor and/or outdoor chlorinated pools during infancy# by risk-factor category
0-h CPA>0–20-h CPA>20-h CPAptrend
Subjects n/N (%)OR (95% CI)Subjects n/N (%)OR (95% CI)p-valueSubjects n/N (%)OR (95% CI)p-value
Total56/235 (23.8)1.0 (1.0–1.0)29/95(30.5)1.24 (0.69–2.23)0.4642/100 (42.0)2.25 (1.32–3.85)0.003<0.001
Schools with >50% response rate35/146 (24.0)1.0 (1.0–1.0)17/59(28.8)1.24 (0.57–2.7)0.5923/58 (39.7)2.25 (1.10–4.59)0.030.03
High parental educational level36/156 (23.1)1.0 (1.0–1.0)22/72(30.6)1.31 (0.67–2.57)0.4334/82 (41.5)2.26 (1.22–4.18)0.0090.003
Parents with no asthma/respiratory allergies17/115 (14.8)1.0 (1.0–1.0)13/38 (34.2)4.31 (1.55–12.0)0.00518/45 (40.0)4.45 (1.82–10.9)0.0010.001
No breastfeeding19/66 (28.8)1.0 (1.0–1.0)7/12 (58.3)1.06 (0.55–2.06)0.8612/22 (54.6)2.10 (1.11–3.98)0.020.008
No day-care centre attendance21/133 (15.8)1.0 (1.0–1.0)9/32 (28.1)2.35 (0.87–6.38)0.0915/36 (41.7)4.44 (1.88–10.5)0.007<0.001
No maternal smoking during pregnancy46/203 (22.7)1.0 (1.0–1.0)21/77 (27.3)1.27 (0.65–2.49)0.4834/87 (39.1)2.16 (1.20–3.90)0.010.005
No exposure to parental smoking38/161 (23.6)1.0 (1.0–1.0)19/65 (29.2)1.16 (0.57–2.35)0.6132/75 (42.7)2.21 (1.18–4.17)0.010.004
No older siblings16/99 (16.2)1.0 (1.0–1.0)13/45 (28.9)2.26 (0.87–5.88)0.0916/47 (34.0)2.72 (1.13–6.56)0.030.01
No use of bleach for house cleaning48/201 (23.9)1.0 (1.0–1.0)28/87 (32.2)1.37 (0.75–2.51)0.3036/87 (41.4)2.22 (1.25–3.95)0.0070.003
  • Odds ratios (ORs) were adjusted for breastfeeding, sex, number of older siblings, area of residence, day-care centre attendance, maternal smoking during pregnancy and parental antecedents of atopic disease (except when the factor was excluded). A high level of education means that the father and/or mother graduated from a university or high school. N: number of subjects in group; CI: confidence interval; ptrend: p-value for trend. #: before the age of 2 yrs.