Chlorinated pool attendance, atopy, and the risk of asthma during childhood

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.

Figure 1

Prevalence of children with doctor-diagnosed or total asthma (A), with elevated eNO (B), or with doctor-diagnosed or total asthma and/or elevated eNO (C) according to the CPA in children with low or high total serum IgE. Total asthma refers to asthma diagnosed by a doctor and/or screened with the EIB test. The cutoff value of 56 kIU/L for total serum IgE corresponds to the 50th percentile of concentrations observed in the studied population. Statistical significance assessed by a chi-square test for trend.

Figure 2

Prevalence of children with high total serum IgE or with aeroallergen-specific serum IgE according to CPA [error bars indicate 95% confidence interval (CI)]. The cutoff value of 56 kIU/L for total serum IgE corresponds to the 50th percentile of concentrations observed in the studied population. Numbers above error bars are upper limits of 95% CIs.

Figure 3

Risk of developing asthma (total asthma, i.e., diagnosed by a doctor or screened with the EIB test) or of having elevated eNO (> 30 ppb) according to total serum IgE level and CPA over increasingly shorter periods of time after birth. The ORs have been adjusted for covariates listed in Table 2. The cutoff value of 56 kIU/L for total serum IgE corresponds to the 50th percentile of concentrations observed in the studied population.