Poorly maintained spa pools could be a breeding ground for Legionnaires' disease, experts have warned.
An ideal breeding ground for disease?
The Health Protection Agency is calling for mandatory testing of spa pools, the high temperatures of which are said to be ideal for the legionella bacterium.
The HPA's annual conference will be told tests on 88 spa pools revealed that 23 contained the bacterium.
Sixteen of the 23 had already passed tests for the accepted safety levels of microbiological contamination.
During 2003, there were 27 cases of Legionnaires' disease in England where spa pools were identified as the source of infection, with three deaths.
So far this year there has been one case of Legionnaires reported to be associated with a spa pool.
Lead researcher Dr Susanne Surman-Lee said: "In every spa pool-related outbreak that we have investigated, the pool had not been managed or designed according to guidelines, or had poorly trained staff.
Legionnaires' disease is caused by the bacterium Legionella pneumophila.
The majority of cases are reported as single, isolated cases but outbreaks can occur.
There are about 300 cases reported each year in the UK.
It mainly affects people over 50 and generally more men.
Early symptoms include a 'flu-like' illness with muscle aches, tiredness, headaches, dry cough and fever.
Deaths occur in 10-15% of the general population.
Legionella infection can be treated with antibiotics and person-to-person spread does not occur.
"In addition, at present, testing for legionella is not mandatory for spa pools.
"Because spa pools are increasing in popularity we need greater recognition and understanding of the risks associated with their use and misuse."
Dr Surman-Lee said sap pools had the potential to cause infection because the high temperatures of the water provided an ideal breeding ground for the legionella bacterium.
This meant that considerable demands were placed upon the disinfection and filtration systems - which had to be properly maintained to cope with the threat.
If the bacterium did start to breed, the jets of water produced by a spa pool could throw the bugs up into the air in aerosol form, and thus they could easily be inhaled by anybody using the pool.
Dr Surman-Lee said: "It's been assumed that if the pool water is satisfactory for routine microbiological checks then growth and spread of legionella would also be under control.
The bacteria that cause the disease
"But we discovered that the legionella bacterium may be present in high numbers in both privately owned and public facilities, even when routine microbiological and safety checks appear satisfactory."
The HPA is preparing new guidance on the health risks associated with spa pools in collaboration with the Health and Safety Executive.
Paul Simons, of the Spa Business Association, said a new system of quality rating of spas would be in place within two years.