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Monday, September 17
16:00 GMT
Swimming pools and child asthma:
even open-air pools seem to increase the risk
finds a Belgian study
Warnings about adverse effects of chlorinated swimming pools,
particularly where they affect children’s airways, are becoming
increasingly prominent in the scientific literature.
The harmful impact of air breathed in close to the chlorinated water
could even be one cause of the upsurge in child asthma recorded in
the industrialised countries.
The 17th Congress of the European Respiratory Society (ERS), where
this issue was the subject of several communications, has just added a
new element to the discussions: children who use chlorinated openair swimming pools have an increased risk of developing asthma.
Asthma is known to be one of the commonest chronic conditions, affecting over 300 million
people worldwide, particularly those who are prone to allergies.
It has multiple causes, but it appears increasingly that chlorinated swimming pools are a factor
linked with an increased risk of asthma onset.
Swimming instructors and poolside staff are in the front line, as reported recently in the European
Respiratory Journal (ERJ) by a Netherlands team, but children and adolescents are also directly
threatened.
Asthma rates doubled
This is illustrated by young competitive swimmers, as seen in the study presented to the Congress
by Vito Brusasco, Giovanni Rossi and their teams, of the University of Genoa and Gaslini
Hospital in Italy.
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The authors studied thirty adolescents, with an average age of 14, who had not previously been
diagnosed with asthma. They measured their level of sensitisation to typical airborne allergens
and their degree of bronchial hyperreactivity; these two elements are generally considered
predictors of asthma onset.
The results presented to the ERS Congress clearly demonstrate a risk to the young swimmers in
regular training for competitions. The Italian team found that 73% of them were sensitised to
airborne allergens, a level almost double that of the general population, and over half of them (17
subjects) suffered from bronchial hyperreactivity.
“We believe that repeated exposure to high concentrations of chlorine in the ten centimetres of air
above the water’s surface is damaging to the airways”, the authors told the Congress. “It could
favour allergen sensitisation and contribute to the development of bronchial hyperreactivity as
well as the onset of asthma symptoms in children.”
Open-air swimming pools now also suspected
It was a Belgian team that brought really astounding news to the Congress.
The received wisdom was that harmful levels of airborne chlorine were only found in covered
swimming pools: it seemed logical that the enclosed air would be rich in lung-irritating gases,
especially chloramines, produced by the chemical reaction between chlorine and various organic
substances, including sweat, urine and saliva.
Yet an original study presented to the ERS Congress by Marc Nickmilder, Alfred Bernard and
Catherine Voisin, of the Catholic University of Louvain’s Department of Toxicology, shows that
this risk can also affect regular users of open-air pools.
The Louvain team examined 847 adolescents, aged 15 years on average, enrolled at three Belgian
secondary schools. One school was chosen because the timetabled swimming lessons took place
in a non-chlorinated pool, disinfected by means of a copper-silver ionisation system, which meant
its pupils could be used as a control group.
The study was conducted on the basis of both questionnaires completed by parents and blood
tests. The questionnaires elicited information on family antecedents for asthma or allergies, the
adolescent’s lifestyle and, above all, the number of hours spent in chlorinated and nonchlorinated, enclosed and open-air pools.
The blood tests sought to determine levels of immunoglobin E (IgE), an antibody associated with
an increased risk of allergies and asthma.
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Risk multiplied up to nine times
The conclusions revealed in Stockholm by Nickmilder leave little room for doubt. “Use of openair swimming pools correlates strongly with atopy levels as measured by serum IgE concentration
and considerably increases the asthma risk”, the researcher explains.
The results presented to the Congress show that adolescents who, up to the time of the study, had
spent a total of more than 500 hours in open-air swimming pools, had a risk of developing asthma
three times higher than those who had never swum in a chlorinated pool.
"The relative risk is as much as nine times in subjects with high IgE, even where the parents have
no asthmatic antecedents”, Bernard emphasised at the Congress.
So this sounds an important warning, coming as it does at a time when young children are
increasingly being taken to swimming pools.
Following hard on the heels of a discovery by the same team that so-called "water-babies" had
higher asthma rates than their peers at age ten, the latest revelations in Stockholm should lead to
some serious reconsideration of the issues.
“We would recommend that open-air pools should not be too heavily chlorinated, especially if
young children use them”, the Belgian team told the Congress.
Contacts:
Vito Brusasco
Tel: +39 010 353 76 90
E-mail: vito.brusasco@unige.it
Marc Nickmilder
Tel: +32 2 764 53 48
E-mail: marc.nickmilder@toxi.ucl.ac.be
Alfred Bernard
Tel: +32 2 764 53 48
E-mail: bernard@toxi.ucl.ac.be
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