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Safeguard OSH Solutions - Thomson Reuters

Safeguard Magazine

Health matters—Legionella warning

The rate of infection with Legionnaires’ disease has increased markedly in the last 12 months, but a much quicker testing method is now available. LOUISA GEORGE reports.

In the last year in New Zealand we have seen some of the highest rates of infection with Legionnaires’ disease ever recorded. In the first few weeks of January this year, for example, there were at least 29 confirmed cases nationwide.

One of the most concentrated outbreaks was at the end of last year at a plant in Pahiatua, where 13 contractors were affected. In February, the hot water system at a small South Island hospital was found to be infected and patients had to be sponge bathed to reduce the risk of exposure. Legionella bacteria were also found in the spa pool within a public swimming pool complex in Auckland.

Legionnaires’ disease was first recognised in Philadelphia in 1976 at the American Legion Convention where several hundred people came into contact with aerosol water-borne legionella pneumophila bacteria from the building’s cooling tower. Thirty-four Legionnaires died. It was from this outbreak that the disease and the bacteria got its name; Legionella after the infected legionnaires, and pneumophila meaning “lung-loving”.

Legionella bacteria are found in both natural and artificial environments. The bacteria thrive in conditions that are warm (optimally 32-42°C), and nutrient-rich eg biofilm, scale, corrosion.

Legionnaires’ disease is initially categorised by a loss of appetite, lethargy and a mild unproductive cough, though other symptoms are difficult to pin down and not everyone exposed will develop symptoms. The average incubation period ranges two to ten days with a 40 to 80 percent fatality rate. Early detection and treatment usually results in full recovery, though pulmonary scarring may continue in some patients who suffer severe respiratory failure.

Those with an increased susceptibility to the disease include the elderly, heavy smokers and drinkers, and people with cancer, chronic respiratory diseases, kidney disease, or immuno-suppressed conditions. Men over 40 are more susceptible to contracting the disease, with males in general being twice as susceptible as females.

Approximately 85% of outbreaks internationally are caused by exposure to the water-borne Legionella pneumophila serotype. Outbreaks associated with potting mixes and compost are exclusively from exposure to the Legionella Longbeachae serotype. Other lesser known serotypes have also been implicated in infections, eg Legionella micdadei and Legionella bozemanii.

Human alteration of the environment can be thanked for the prevalence of legionellosis. Common places the bacteria can be found to thrive are in potable water systems, cooling towers, evaporative condensers, health care facilities, hotels, ships, natural spas, hot tubs and swimming pools. All have an increased likelihood of stagnant water, warm conditions and high nutrient levels, promoting the growth of legionella bacteria.

In order to control legionella bacteria levels in artificial water systems it is important to have a robust understanding of the factors that influence the survival and growth of the bacteria. With this knowledge the areas most at risk can be identified and control measures – such as chemical dosing – can be put in; along with assurances by sampling and testing that the control measures are effective.

The World Health Organisation has developed a framework for assessing and managing the risk of legionella. This can be found in the document Legionella and the Prevention of Legionellosis. WorkSafe New Zealand has also provided the document Preventing Legionnaires’ Disease.


Currently the recognised approach to identifying and counting Legionella bacteria in this country is the culture method. However an alternative testing method has become available in New Zealand called PCR (Polymerase Chain Reaction). PCR is a technique used to amplify trace amounts of DNA in a sample to produce a quantitative result. The same technique is also used to detect PSA (Pseudomonas syringae pv. actinidae) in Kiwifruit, and salmonella and listeria in food products.

PCR detects both viable and non-viable Legionella bacteria including any that are encased in protozoa. The culture method measures viable bacteria – the dangerous ones – but doesn’t always identify bacteria encased in protozoa.

The use of PCR testing for Legionella bacteria has enabled us at Genesis Energy to risk profile our cooling towers and provide us with confidence in our Legionella Risk Management Plan. A one-day turnaround time enables a fast response, compared with the culture method which yields a result after two weeks.

PCR analysis has given Genesis Energy the ability to determine that Legionella bacteria are transient through our towers, and has given us knowledge of the environmental factors in the Waikato River which trigger an increase in the naturally occurring levels of the bacteria.

As we prepare for what is looking like another hot and humid summer, it behoves all of us with systems with the potential for Legionella bacteria growth to take all steps practicable to ensure we are controlling and monitoring the levels of bacteria to protect our people and communities.

Louisa George is chemical and water services manager with Genesis Energy.

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