Cooling Tower Registries and Building Water Management Plans: Strategies to combat Legionnaires’ Disease

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Monday, January 20, 2020
Juliette O’Keeffe, Laura Zettler and Victoria Colling

There’s something in the aerosols

Devices that aerosolize water can increase the risk of exposure to Legionella bacteria through inhalation, leading to serious illness such as Legionnaires’ disease and a milder flu-like illness called Pontiac fever. One of the most serious legionellosis outbreaks in Canadian history was in Toronto in 2005, where 135 people were affected and 23 died as a result. In the past decade, there have been other significant legionellosis outbreaks across Canada:

The reported occurrence of legionellosis is on the rise in Canada and the USA, which may be due to many factors, including improved diagnosis and reporting practices, aging water infrastructure and an aging population.

Sources of exposure can include shower heads, hot tubs and decorative fountains but the majority of outbreak-related deaths are associated with cooling towers. Each of the outbreaks listed above were attributed to cooling towers. Fortunately, most outbreaks caused by Legionella bacteria can be prevented with more effective building water management. Measures to assist public health to identify and respond to the source of outbreaks more quickly (e.g. by using cooling tower registries), and improving the ability of building owners and managers to reduce risks through water management plans can reduce the number of cases of legionellosis.

Legionella in the built environment

Although Legionella is naturally present in the environment, the greatest risk of exposure arises in buildings. Buildings with large and complex plumbing systems can provide areas with optimal conditions for survival and growth of Legionella. This can include warm water temperatures (e.g. 25-50°C), areas of stagnation, lack of disinfectant residual and the presence of biofilms that form in storage containers, corroded pipes or outlets where Legionella can be sheltered from disinfectants and survive or multiply. People are subsequently exposed by inhalation when the infected water becomes aerosolized by cooling towers, shower heads, or other features that produce steam, mists or fine aerosols such as hot tubs or decorative water features. Cooling towers, often located on top of buildings, use water to disperse heat from buildings through evaporation to the atmosphere. The combination of standing water, warm temperatures and production of mist through evaporation that can be dispersed from a high point of a building creates ideal conditions for the growth and subsequent dispersal of Legionella over a large area.

Identifying the source with cooling tower registries

Cooling tower registries allow for much quicker identification of the source of an outbreak, and the requirement for maintenance and monitoring reduces the potential for Legionella bacteria to survive and grow thus reducing outbreak occurrence. The City of Hamilton was the first in Canada to require mandatory cooling tower registration following outbreaks in 2006 and 2008. Similarly, following the outbreak in Quebec in 2012, new regulations were developed for mandatory cooling tower registration in the province and requirements for preventive maintenance and routine monitoring for Legionella pneumophila. The approach has resulted in reduced occurrence of Legionella in building water systems, and potentially avoided incidences of legionellosis. Following the outbreak in Moncton in 2019, officials there are now calling for introduction of cooling tower registries.

The City of Vancouver, which has not experienced a major outbreak, is taking the proactive measure of establishing cooling tower registries requiring all new and existing cooling towers and evaporative condensers to have an operating permit as of January 1, 2020. The registry will also cover all decorative water features as of July 1, 2020, and the new regulation will also require monitoring and preventive maintenance that will help to reduce the risk of outbreaks.

Improving Water Management

Along with cooling tower registries, Water Management Programs can provide a focus on steps to reduce the conditions that favour Legionella survival and growth within buildings. This involves identifying key risks in a building plumbing system and taking measures to reduce these risks. Preventive measures can include maintaining water temperatures outside Legionella’s ideal growth range (e.g. keeping hot water systems >50 °C and cold water systems < 25 °C), preventing water stagnation (e.g. weekly flushing), ensuring disinfection residuals are sufficient to control biofilm (e.g. 0.5 – 1.0 mg/L free chlorine residual before it reaches users) and regular monitoring. Buildings such as hospitals may require additional measures to protect vulnerable users, such as secondary disinfection, additional flushing frequency or added measures to ensure temperature requirements can be achieved.

Where to learn more

Education and training resources can help to equip building owners, facility managers, drinking water system owners and operators, public health inspectors and healthcare professionals to develop and deliver effective water management plans. Organisations such as the US Centre for Disease Control has developed online toolkits and in  Ontario, the Walkerton Clean Water Centre has collated online Legionella resources and has provided  training on "Managing Legionella Risk in Buildings through Water Safety Management Planning".  The NCCEH has also compiled recent relevant resources on Legionella specific to our public and environmental health audience.

For more information visit our Legionella topic page and register for our upcoming webinar “Strategies to combat Legionnaires’ Disease – Outbreak investigations and Preventive Policy”.

NOTE: The NCCEH would like to thank Laura Zettler and Victoria Colling from the Walkerton Clean Water Centre​ for their invaluable contributions in the creation of this blog article.