Legionnaires’ disease is recognised worldwide as an important cause of both community- and hospitalacquired pneumonia. It is caused by Gram-negative bacilli of the Legionella genus. The mortality rate in infected individuals ranges between 10 – 20%. It was named after a large outbreak in 1976 that occurred at a meeting of the American legion, which affected 221 people, causing 34 deaths. Legionella bacteria are common and can be found naturally in environmental water sources, including rivers, lakes, natural pools and moist soil. Water temperatures in the range of 20°C to 50°C favour growth of the organism. Legionella pneumophila serogroup 1 is the most important species of Legionella that causes disease in humans, although other species can occasionally cause disease. Legionella spp. may also cause Pontiac fever, a mild, self-limiting flu-like illness.