Legionnaire's disease is an acute respiratory infection caused by the bacteria Legionella pneumophila.
The bacteria that cause Legionnaire's disease have been found in water delivery systems and can survive in the warm, moist, air conditioning systems of large buildings, including hospitals.
Spread of the bacteria between humans has not been proven.
Most infection occurs in middle-aged or older people, although it has been reported in children. Typically, the disease is less severe in children.
Risk factors include: