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Alfred Bernard,¹ Sylviane Carbonnelle,¹ Claire de Burbure,¹ Olivier Michel,² and Marc Nickmilder¹

¹Department of Public Health, Catholic University of Louvain, Brussels, Belgium; ²Clinics of Allergology and Respiratory Diseases, Free University of Brussels, Brussels, Belgium

Abstract
The pool chlorine hypothesis postulates that the rise in childhood asthma in the developed world could result at least partly from the increasing exposure of children to toxic gases and aerosols contaminating the air of indoor chlorinated pools. To further assess this hypothesis, we explored the relationships between childhood asthma, atopy, and cumulated pool attendance (CPA) . We studied 341 schoolchildren 10–13 years of age who attended at a variable rate the same public pool in Brussels (trichloramine in air, 0.3–0.5 mg/m³) . Examination of the children included a questionnaire, an exercise-induced bronchoconstriction (EIB) test, and the measurement of exhaled nitric oxide (eNO) and total and aeroallergen-specific serum IgE. CPA by children (range, 0–1,818 hr) emerged among the most consistent predictors of asthma (doctor diagnosed or screened with the EIB test) and of elevated eNO, ranking immediately after atopy and family history of asthma or hay fever. Although the risk of elevated eNO increased with CPA [odds ratio (OR) = 1.30 ; 95% confidence interval (CI) , 1.10–1.43] independently of total or specific serum IgE, the probability of developing asthma increased with CPA only in children with serum IgE > 100 kIU/L (OR for each 100-hr increase in CPA = 1.79 ; 95% CI, 1.07–2.72) . All these effects were dose related and most strongly linked to pool attendance before 6–7 years of age. Use of indoor chlorinated pools especially by young children interacts with atopic status to promote the development of childhood asthma. These findings further support the hypothesis implicating pool chlorine in the rise of childhood asthma in industrialized countries. Key words: aeroallergens, atopy, childhood asthma, chlorine, exercise-induced asthma, exhaled nitric oxide, nitrogen trichloride, swimming pool, total IgE, trichloramine. Environ Health Perspect 114:1567–1573 (2006) . doi:10.1289/ehp.8461 available via http://dx.doi.org/ [Online 8 June 2006]

Address correspondence to A. Bernard, Unit of Toxicology, Catholic University of Louvain, 30.54 Clos Chapelle-aux-Champs, B-1200 Brussels, Belgium. Telephone: 32-2-7643934. Fax: 32-2-7643228. E-mail: bernard@toxi.ucl.ac.be

This work was supported by grant IBGE 747 of the Brussels Capital Region and the European Union (HELIOS project, CT 99 QLK4-1308 ; A.B., coordinator) . A.B. is Research Director of National Fund for Scientific Research, Belgium.

The authors declare they have no competing financial interests.

Received 4 July 2005 ; accepted 8 June 2006.