Investigators have found traces of the bacteria that cause Legionnaire's disease in the hot water systems of 11 medical institutions in canton Graubünden. However no one has been infected by the potentially life-threatening bacteria, according to the authorities.

The discovery came after the canton's laboratory carried out tests of hot water systems in 69 hospitals, clinics, homes nursing homes and convalescent centres. In many of the 11 cases, experts were able to remove or significantly reduce the level of the bacteria, which cause acute respiratory infection.

In five cases, the bacteria level was so small that no action was taken. In the other six cases, the levels exceeded the safety limit of 1,000 organisms per litre of water and the hot water systems concerned were immediately disinfected.

Legionella bacteria can be found in many different types of water systems and can cause both Legionnaire's disease and the flu-like Pontiac fever. Legionnaire's disease acquired its name in 1976 when an outbreak of pneumonia occurred at an American Legion convention in Philadelphia, in the United States.

The bacteria flourish in hot water and air conditioning systems with a temperature of between 25 and 45 degrees centigrade. Outbreaks of the disease occur when people inhale the bacteria.

The best method of preventing the spread of the Legionella bacteria, according to the cantonal laboratory, is to maintain water temperatures at between 50 and 60 degrees centigrade.

swissinfo with agencies