Legionellosis (also known as Legionnaires Disease or Pontiac Fever) is caused by bacteria that occur naturally in the environment. About 50 different strains of Legionella bacteria are known. One strain of bacteria called Legionella pneumophilla has been responsible for illnesses linked to some types of air conditioning systems in buildings. Another strain called Legionella longbeachae occurs in soils, composts and potting mixes, and is responsible for more than half of all New Zealand cases.
The disease is more common in middle-aged and older people, smokers, people with underlying lung disease and other long term conditions such as diabetes, and those with weaker immune systems. If you come into one of these categories you should be especially careful to take precautions.