Health Stream Literature Summary - Issue 56 - December 2009

Impact of chlorinated swimming pool attendance on the respiratory health of adolescents.
Bernard A, Nickmilder M, Voisin C and Sardella A. (2009) Pediatrics, 124(4); 1110-1118.

Swimming pools are most commonly disinfected with chlorine-based disinfectants which inactivate a wide spectrum of waterborne pathogens, however there are also some disadvantages including irritation of the skin, eyes and upper respiratory tract of swimmers in contact with pool water or air. It has been known for several years that elite swimmers have a higher prevalence of respiratory symptoms, asthma and airway inflammation than other athletes. It has been assumed that this was due to selection bias attributable to the lower asthma producing potential of indoor swimming compared with other sports (i.e. that people diagnosed with asthma are encouraged to swim as a preferred form of exercise). It is now being increasingly acknowledged that these respiratory problems may be attributed, at least in part, to chlorine disinfection of pool water. Recent studies have found that indoor chlorinated pools may be detrimental to the airways of children causing epithelial damage and increasing asthma risk as well as contributing to the development of allergic diseases. The aim of this study was to assess for the first time the overall impact of chlorinated pool exposure on the respiratory health of adolescents by considering the total time spent in indoor and outdoor chlorinated pools.

Adolescents were recruited from 3 secondary schools in the southern part of Belgium, in the cities of Louvain-la-Neuve, Bastogne and Lessines. Students in Louvain-la-Neuve had access to an indoor pool disinfected with the copper-silver method, whereas students at the other two schools could visit only indoor pools disinfected with chlorine. Parents completed a questionnaire asking about the health of their child and risk factors for asthma and allergic diseases. The questionnaire also included questions intended to estimate the total time the child had spent in indoor or outdoor chlorinated pools. Students were examined in schools and measured for height and body weight and questioned about respiratory symptoms. A blood sample was collected and screening undertaken for exercise induced bronchoconstriction (EIB). Asthma was defined either as 'ever asthm' corresponding to asthma diagnosed at any time by a physician, or as 'current asthma' corresponding to physician-diagnosed asthma that was currently being treated with medication and/or was associated with positive EIB test results. Allergies were screened for by measuring total and aeroallergen-specific immunoglobulin E (IgE) concentration in serum and participants were classified as nonatopic or atopic on the basis of this. Associations between outcomes and cumulative chlorinated pool attendance (CPA) were assessed in four categories, less than 100 hours, 100 to 500 hours, 500 to 1000 hours or greater than 1000 hours.

Over 70% of eligible students at the three schools participated, giving 847 subjects aged 13 to 18 years. The three groups had significant variation in several baseline characteristics associated with asthma risks (eg breastfeeding, childcare attendance, maternal smoking during pregnancy), however these were adjusted for in statistical analysis. As expected, students in Louvain-la-Neuve had much lower CPA levels than students in the two other cities. A subgroup of 114 students with a lifetime CPA value of less than 100 hours was chosen as the reference group. The associations between chlorinated pools and outcomes studied were examined with increasing cumulative CPA. The rate of sensitization to major aeroallergens did not vary with CPA, whereas the total serum IgE concentrations showed a tendency to decrease. There was little variation found in FEV1 values, showing only a modest increase between lowest and highest CPA categories. Prevalences of wheezing and EIB, although increasing in all groups with CPA values of greater than 100, did not show any significant exposure-related trend. However, the prevalences and odds of ever asthma, current asthma, cough and shortness of breath increased almost linearly with the time spent in chlorinated pools. Even when adolescents with a diagnosis of asthma were excluded, cough and shortness of breath persisted (P for trend of .004 and .05 respectively). The risk of hay fever was increased in all groups with CPA values of greater than 100 hours whereas the risk of allergic rhinitis was only increased in the group with the highest CPA value.

The risks of respiratory symptoms and asthma associated with CPA were strongly affected by atopic status. Of those adolescents with atopy with serum IgE levels of greater than 30 KIU/L or aeroallergen-specific IgE, the odds ratios (ORs) for asthma symptoms (wheezing, cough, shortness of breath) and for ever or current asthma increased with the lifetime number of hours spent in chlorinated pools, with an OR of 7.1 to 14.9 when chlorinated pool attendance was greater than 1000 hours. Adolescents with atopy with CPA greater than 100 hours had greater risk of hay fever (OR 3.3-6.6) and those with attendance of greater than 1000 hours had a greater risk of allergic rhinitis (OR 2.2-3.5). These associations were not found among those without atopy or among those who attended a copper-silver pool. The population attributable risks (PARs) for atopic diseases associated with CPA were calculated by considering as exposed the students with atopy who had spent more than 100 hours in chlorinated swimming pools. When atopy was defined on the basis of total serum IgE levels then PARs for ever asthma were 63.4%, for current asthma, 79.2%, for hay fever, 62.1% and for allergic rhinitis, 35.0%. Similar PAR estimates were obtained when atopy was defined as sensitization to any aeroallergen. This study shows that CPA during childhood interacts with atopic status to increase the risk of asthma, hay fever and allergic rhinitis. The authors postulate that chlorination products may disrupt epithelial barriers, enhancing penetration of allergens. Differences in exposure-response relationships between hay fever and asthma may reflect primarily differences in the doses of chlorination products deposited in the upper and lower respiratory tract respectively.

Comment This cross sectional study cannot establish a temporal relationship between exposure to chlorinated swimming pools and development of respiratory symptoms, only that the observed associations exist in this population. A prospective study would be required to determine when development of symptoms or atopy occurs relative to pool exposure.

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