Legionella Control with Chlorine Dioxide

What is Legionella?

Legionella is a bacteria that is common in many environments, with at least 50 species and 70 serogroups identified.

Legionella live within amoebae in the natural environment. Legionella species are the causative agent of the human Legionnaires' disease and the lesser form, Pontiac fever, which gives flu-like symptoms.

Legionella transmission is via the inhalation of water aerosols (water mist droplets) containing the bacteria. Common sources of aerosols include cooling towers, domestic hot and cold water systems, fountains, irrigation sprays and similar disseminators. Natural sources of Legionella include freshwater ponds and creeks.

Amoebae are closely associated with biofilm formation. Legionella multiply inside the amoeba until the amoeba bursts releasing huge numbers of Legionella bacteria into a water system. If this water is then aerosolized, as from a cooling tower, jacuzzi bath, shower, etc, and the aerosol is inhaled, Legionnaire's Disease can be the result.

The Role of Biofilm

Health and Safety Agencies worldwide, and the World Health Organization all recognize that biofilm plays a key role in providing conditions for Legionella to proliferate in a water system. They therefore recommend strategies that will control the growth of biofilm and reduce the risk of Legionnaire's Disease.

The traditional strategy is one of disinfection with chlorine in the form of hypochlorite followed by temperature control, with hot water stored at > 140^o F and distributed to maintain > 122^o F, and cold water maintained below 68^o F. But maintaining these temperature controls does not guarantee freedom from Legionella growth and can be hard to maintain.

For example, cold water systems in warm weather can have temperatures over 68^oF; cold water pipes running beside hot water pipes suffer the same problem; and while water can be stored at > 140^oF it is difficult to maintain in the distribution system, especially in larger buildings.

However, research has shown that chlorine dioxide dosed at drinking water approved levels is effective, not only for controlling Legionella but also for controlling biofilm growth.

This substantiates research¹ in the field over 10 years that has proven that continuous treatment with chlorine dioxide is effective in controlling Legionella in large complex hot and cold water systems, both new and old, in hard or soft water, and at varying pH.

At 140o F (60o C) - Legionella dies instantly - pasteurization occurs.

At 131o F (55o C) - 95% die

122 to 131o F (50 to 55o C) - Can survive but do not multiply

95 to 115o F (35 to 46o C) - Ideal growth range

68 to 122o F (20 to 50o C) - Growth range

Below 68o F (20o C) - Can survive but are dormant, even below freezing

1 Legionella in Hospital Water Supplies: the "Scottish" Picture, Dr John Hood Glasgow Royal Infirmary

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