Infant swimming in chlorinated pools and the risks of bronchiolitis, asthma and allergy

C Voisin; A Sardella; F Marcucci; A Bernard

doi:10.1183/09031936.00118009

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	p_trend
			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; p_trend: 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			p_trend
	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; p_trend: 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.