Legionella the bacteria

Legionella in the environment

Legionella bacteria are widely distributed in the natural environment and have been isolated from water sources, including lakes, rivers, streams, groundwater, thermal lagoons, and habitats such as soils and mud. Legionella obtain nutrients from other microorganisms such as algae, protozoa and other bacteria as well as from the utilisation of some organic and inorganic material. The organism multiplies at temperatures ranging from 20-45ºC, with maximum growth occurring at between 32-43ºC. They can survive freezing and are killed with increasing rapidity as temperatures exceed 45ºC. Survival time decreases from hours at 50ºC to minutes at 60ºC, while at 70ºC the organism is destroyed almost immediately.

Legionella from natural sources can enter and colonise manufactured water systems such as cooling water systems (incorporating cooling towers and evaporative condensers), hot water and warm water supply services, spa pools, spa baths, hydrotherapy pools, air-houses, humidifiers, nebulisers and decorative fountains.

Legionella & illness

Legionella bacteria must be inhaled to cause illness, however most people who are exposed to Legionella do not become ill. Legionella generally infects the lung causing pneumonia and a disease known collectively as legionellosis. Legionellosis can take the form of the pneumonic, often very severe and potentially fatal Legionnaires' disease or the non-pneumonic, often non-fatal Pontiac fever. The incubation period (time between being infected and developing symptoms) for legionellosis infection is 2-10 days, and symptoms include flu-like symptoms including fever, chest pain, cough, breathlessness and diarrhoea.

Diagnosis is usually made by a series of blood tests, however infections caused by the species Legionella pneumophila serogroup 1 may be identified rapidly by testing a sample of urine. Legionellosis infection generally requires treatment with antibiotics and some cases may require admission to hospital. Severe cases of L. pneumophila serogroup 1 infection will need to be treated in hospital and may require intensive care.

Legionella infections are a notifiable disease in South Australia, meaning the doctor and laboratory diagnosing the disease are required to notify all cases to the Communicable Disease Control Branch of the South Australian Department of Health.

At risk groups

Legionella infection or illness can result from the inhalation of aerosols containing Legionella bacteria which may be generated by some manufactured water systems. However, most people who are exposed to the organism do not become ill. The risk of illness is increased by:

● Being of male sex (possibly related to smoking)
● Smoking
● Chronic heart and lung disease
● Diabetes
● Kidney failure
● Some forms of cancer
● Being over the age of 50

Useful fact sheets

» Legionnaires' Disease - Reducing Risks in the Home (Department of Health SA)
» Enjoy gardening without the risk of Legionella longbeachae (Department of Health SA)

Sources:
Guidelines for the Control of Legionella in Manufactured Water Systems in SA