MedWire News: Children who regularly swim in chlorinated swimming pools, both indoor and outdoor, are at higher risk for developing asthma than children who do not, according to two studies presented this week at the European Respiratory Society annual congress in Stockholm, Sweden.

An Italian team described how young competitive swimmers, who regularly trained in an indoor pool, had a much higher rate of allergic sensitization than would be expected. Some of these children also had bronchial hyperreactivity (BHR) to methacholine.

Meanwhile, Belgian researchers presented data that showed how regular attendance at an open-air pool can increase immunoglobulin (Ig)E levels and asthma risk in children.

The premise behind both studies is that toxic chlorination products just above the surface of the water can damage the airways of children if breathed regularly enough.

"The levels of chlorine gas concentration 10 cm above the surface of water of an indoor swimming pool may be very high, and exposure to this irritant gas [is] toxic to the airway epithelium," explained Vito Brusasco and colleagues from the University of Genoa and Gaslini Hospital.

They studied 30 children with a mean age of 13.6 years who regularly competed in swimming competitions and were thus often exposed to the chlorinated products in an indoor pool.

None of the children had asthma before the investigation started, but the researchers found that 73% were sensitized to common aeroallergens, 1.7 times higher than the expected prevalence rate of 41%. BHR was found in 94% of 17 sensitized and one of the nonsensitized children.

Brusasco and team speculate that repeated exposure to toxic chlorination products damages the bronchial epithelium which makes children more susceptible to sensitization and subsequent BHR.

The risk of asthma does not appear to be confined to indoor pools, as Marc Nickmilder and team, from the Catholic University of Louvain in Brussels, reported.

They studied 360 children with a mean age of 15.4 years recruited from three secondary schools. One of the schools used a non-chlorinated pool so children from that school served as controls.

They found that as children's cumulative attendance at a pool in the open air (CPA) increased, so did the risk of having doctor-diagnosed and total asthma. The adjusted odds ratios for each 100-hour increase in CPA were 1.09 and 1.06, respectively.

"The asthma risk concerned especially subjects with higher total serum IgE," Nickmilder and team said.

They concluded: "We would recommend that open-air pools should not be too heavily chlorinated, especially if young children use them."

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