Legionnaires Info

Legionnaires’ Disease Background

Legionnaires disease was first identified in 1976 following a large outbreak of pneumonia among people who attended an American Legion Convention at the Bellevue Stratford Hotel in Philadelphia.

Legionnaires’ pneumophila is the most frequent cause of human legionellosis, also known as Legionnaires’ disease. Legionnaires’ pneumophila is responsible for between 70-90% of all outbreaks. Legionnaires’ pneumophila can only be acquired from an environmental source; infection does not occur between humans or humans and animals.

It is normally contracted by inhaling the legionella bacteria in tiny droplets of water (aerosols), deep into the lungs. The incubation period is between 2-10 days (usually 3-6 days) and infection with legionella bacteria can be fatal in approximately 12% of reported cases.
Legionella bacteria are common and can be found naturally in environmental water sources such as lakes, rivers and reservoirs, usually in low numbers. Legionella bacteria can survive under a wide range of environmental conditions and found in water temperatures between 6 ºC and 60 ºC. Water temperatures between 20 ºC to 45 ºC seem to favour growth. The organisms do not appear to multiply below 20 ºC and will not survive above 60 ºC.

Legionella bacteria also require a supply of nutrients to multiply. Sources can include organisms within the water system itself such as algae, amoebae and other bacteria. The presence of sediment, sludge and scale within the system, together with biofilms, are also thought to play an important role in harbouring and providing favourable conditions in which the legionella bacteria may grow.

As legionella bacteria are commonly encountered in environmental sources they could eventually colonise manufactured water systems, such as cooling towers, hot and cold water systems and other plant which use or store water. To reduce the possibility of creating conditions in which the risk from exposure to legionella bacteria is increased, it is important to control the risk by introducing measures which:

(a) Do not allow proliferation of the organisms in the water system.
(b) Reduce, so far as is possible the exposure to water droplets and aerosol.