Legionella bacteria and water systems in health care premises.

Legionnaires' disease (Legionellosis) is a bacterial pneumonia that acquired its name following an outbreak of pneumonia among army veterans attending an American Legion convention in Philadelphia in 1976. The previously undiscovered bacterium that caused this form of pneumonia was therefore named Legionella. There are more than 45 species of Legionella bacteria and these are natural inhabitants of water supplies throughout the world (Fliermans, 1981). About half of these have been associated with infection, although the most common cause of Legionnaires' disease is Legionella pneumophila, which is the causative strain in around 90 per cent of cases (Fields et al, 2002).