Legionnaires' Disease is caused by a bacterium called legionella pneumophila and is contracted by breathing in droplets of water that contain the bacterium.
Hot-tubs and spas should be kept at the correct pH, sanitation and alkalinity levels. They should be tested "at least once a week" with litmus paper, says Mr Mark Howlett, director of Castle Pools in Dublin. If any of these is not correct, the relevant chemicals should be added to the water. The water should be totally changed "at least once a fortnight," he says.
To avoid infection from domestic showers, hot water should be run through the piping at a temperature of between 50 and 60 degrees, any lengths of pipe/showers/taps not regularly used should be flushed through frequently and shower heads should be cleaned regularly.
Most people who are exposed to legionella don't become ill and Legionnaires' Disease does not spread from person to person.