Tables
- Table 1– Characteristics of children who swam during infancy and their controls
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.
- Table 2– Risk of bronchiolitis according to cumulative pool attendance (CPA) at indoor or outdoor chlorinated swimming pools during infancy#
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.
- 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 CPA ptrend Subjects n/N (%) OR (95% CI) Subjects n/N (%) OR (95% CI) p-value Subjects n/N (%) OR (95% CI) p-value Total 56/235 (23.8) 1.0 (1.0–1.0) 29/95(30.5) 1.24 (0.69–2.23) 0.46 42/100 (42.0) 2.25 (1.32–3.85) 0.003 <0.001 Schools with >50% response rate 35/146 (24.0) 1.0 (1.0–1.0) 17/59(28.8) 1.24 (0.57–2.7) 0.59 23/58 (39.7) 2.25 (1.10–4.59) 0.03 0.03 High parental educational level 36/156 (23.1) 1.0 (1.0–1.0) 22/72(30.6) 1.31 (0.67–2.57) 0.43 34/82 (41.5) 2.26 (1.22–4.18) 0.009 0.003 Parents with no asthma/respiratory allergies 17/115 (14.8) 1.0 (1.0–1.0) 13/38 (34.2) 4.31 (1.55–12.0) 0.005 18/45 (40.0) 4.45 (1.82–10.9) 0.001 0.001 No breastfeeding 19/66 (28.8) 1.0 (1.0–1.0) 7/12 (58.3) 1.06 (0.55–2.06) 0.86 12/22 (54.6) 2.10 (1.11–3.98) 0.02 0.008 No day-care centre attendance 21/133 (15.8) 1.0 (1.0–1.0) 9/32 (28.1) 2.35 (0.87–6.38) 0.09 15/36 (41.7) 4.44 (1.88–10.5) 0.007 <0.001 No maternal smoking during pregnancy 46/203 (22.7) 1.0 (1.0–1.0) 21/77 (27.3) 1.27 (0.65–2.49) 0.48 34/87 (39.1) 2.16 (1.20–3.90) 0.01 0.005 No exposure to parental smoking 38/161 (23.6) 1.0 (1.0–1.0) 19/65 (29.2) 1.16 (0.57–2.35) 0.61 32/75 (42.7) 2.21 (1.18–4.17) 0.01 0.004 No older siblings 16/99 (16.2) 1.0 (1.0–1.0) 13/45 (28.9) 2.26 (0.87–5.88) 0.09 16/47 (34.0) 2.72 (1.13–6.56) 0.03 0.01 No use of bleach for house cleaning 48/201 (23.9) 1.0 (1.0–1.0) 28/87 (32.2) 1.37 (0.75–2.51) 0.30 36/87 (41.4) 2.22 (1.25–3.95) 0.007 0.003 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.
- Table 4– Risk of respiratory diseases and sensitisation to aeroallergens associated with bronchiolitis in swimming infants and their controls
Controls Swimming infants Bronchiolitis n (%) OR (95% CI) p-value Bronchiolitis n (%) OR (95% CI) p-value No Yes Unadjusted Adjusted No Yes Unadjusted Adjusted Subjects n 179 56 124 71 Wheezing 28 (15.6) 12 (21.4) 1.47 (0.69–3.13) 1.29 (0.47–3.54) 0.62 18 (14.5) 18 (25.4) 2.00 (0.96–4.16) 2.49 (1.13–5.49) 0.03 Asthma 11 (6.2) 4 (7.1) 1.18 (0.36–3.85) 0.91 (0.23–3.70) 0.90 5 (4.0) 11 (15.5) 4.36 (1.45–13.1) 8.27 (2.30–29.6) 0.001 Allergic rhinitis 16 (8.9) 9 (16.1) 1.95 (0.81–4.70) 2.08 (0.79–5.40) 0.14 13 (10.5) 14 (19.7.) 2.10 (0.92–4.76) 4.65 (1.42–15.2) 0.01 Hay fever 19 (10.6) 12 (21.4) 1.40 (0.58–3.41) 0.96 (0.34–2.70) 0.94 6 (4.8) 11 (15.5) 3.61 (1.27–10.2) 4.70 (1.52–14.5) 0.007 Nasal IgE Pollen# 24 (15.7) 3 (6.4) 0.39 (0.11–1.38) 0.57 (0.15–2.10) 0.40 14 (12.8) 13 (20.6) 1.86 (0.80–4.30) 2.63 (1.01–6.80) 0.05 HDM# 15 (9.8) 7 (14.9) 1.62 (0.62–4.25) 2.05 (0.62–6.75) 0.24 9 (8.3) 21 (33.3 ) 2.59 (1.02–6.55) 2.86 (1.07–7.80) 0.04 Cat# 11 (7.2) 3 (6.4) 0.89 (0.24–3.32) 0.90 (0.20–4.18) 0.90 8 (7.3) 7 (11.1) 1.56 (0.54–5.54) 1.26 (0.40–3.96) 0.69 Outcomes are defined in table 1. Bronchiolitis was diagnosed at a mean±sd age of 9.6±5.9 months in infant swimmers and 9.3±5.5 months in controls. The prevalences of respiratory diseases and sensitisation to aeroallergens among children who never developed bronchiolitis did not differ significantly between swimming infants and their controls (p>0.07 for all; Chi-squared test). OR: odds ratio; CI: confidence interval; Ig: immunoglobulin; HDM: house dust mite. #: a total of 153 and 47 controls and 109 and 63 swimming infants, respectively, who did not or did develop bronchiolitis, were tested.