Recreational attendance
Table 2 summarizes studies that have investigated the
respiratory effects of NCl3 and other inhalable CBPs
among recreational swimmers. The first study was conducted among
schoolchildren in Belgium51. While assessing the
effects of ambient air pollution, the authors unexpectedly found that
indoor chlorinated-pools attendance correlated with lung epithelium
hyperpermeability and asthma prevalence. Further studies in Belgium
revealed that the asthma risk among adolescents and children using
chlorinated-pools stems from an interaction with atopic
status52,53. Of interest, also the risk of allergic
asthma was most strongly linked to pool attendance during early
childhood52. Two studies in Sweden confirmed these
observations while showing that the risk of allergic asthma correlated
with the cumulative inhalation exposure to
NCl354,55.
Associations between asthma and recreational swimming in
chlorinated-pools were also reported in Ireland56,
Italy57 and Portugal58. Several
other studies, however, provided no evidence of an increased asthma risk
in recreational swimmers59-62. Of these, one of the
most contradictory but also the most influential owing to its large size
is the UK prospective birth cohort study (ALSPAC
study)61, which was suggestive, if anything, of a
protective effect of swimming towards asthma risk. There are several
possible explanations for these contrasting observations. A first
explanation is that children examined in these negative
studies59-62 were too young to detect associations
with allergic asthma. Another possible explanation is an underestimation
of the exposure with consequently a risk of miss-classifying some
categories of swimmers63,64.
Associations have also been reported between indoor chlorinated-pool
attendance and the risks of allergic rhinitis53,65,
autonomic changes58 and airway inflammation assessed
by the exhaled NO test52. Further complicating the
issue, some studies suggest that early swimming in chlorinated-pools may
increase the risks of allergic sensitization in particular to perennial
allergens62,66,67.
Last, respiratory risks when swimming in chlorinated-pools are probably
not limited to the exposure to NCl3. Swimming in indoor
chlorinated-pools during infancy has also been associated with a higher
risk of bronchiolitis or recurrent respiratory infection mainly in
children with family history of atopic
diseases9,68,69.
Biomarkers studies have revealed that the attendance of
chlorinated-pools correlates with a disruption of airway epithelial
barrier as reflected by altered serum levels of lung epithelium-specific
proteins (pneumoproteins). Several studies have shown that early
swimming in chlorinated-pools is associated with decreased serum levels
of CC169,62,70,71. Lower levels of circulating CC16 in
children are associated with subsequent decreased lung function and
increased risks of developing asthma and other respiratory
diseases71-74.