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Legionella is an opportunistic premise plumbing pathogen (OPPP) that can cause illnesses including Pontiac fever and Legionnaires’ disease, a severe pneumonia named after an outbreak that resulted in 29 deaths following an American Legion Convention in Philadelphia in 1976. Legionella is naturally occurring water borne bacteria that can survive within building water systems and multiply under ideal conditions. These conditions include optimum temperatures for growth (e.g. 25-45°C), stagnant water, lack of disinfectant residual and the presence of biofilms that form in storage containers, pipes or outlets where Legionella can be sheltered from disinfectants and survive or multiply.

Infection occurs via inhalation or aspiration of affected water droplets or aerosols into the lungs. When affected water in cooling towers, shower heads, decorative fountains, hot tubs, or other mists or sprays, becomes aerosolized there is a risk of exposure and subsequent illness among susceptible individuals.  Legionellosis is not caused by ingestion but cases of nosocomial legionellosis have been reported in patients drinking ice water or chewing on ice chips from hospital ice machines infected with Legionella, followed by aspiration of the bacteria into the lungs.

The reported occurrence of legionellosis is on the rise in Canada with the rate of cases per 100,000 persons increasing from an average of 0.29 before 2010 to an average of 0.94 between 2010 and 2017. In 2017 there were over 400 cases in Canada. Smokers, over-50s, and those with compromised immunity are the most at risk of infection and cases occur more often in men than women. The majority of outbreak-related deaths associated with Legionella originate in infected cooling towers.  Major outbreaks in Canada include Toronto in 2005 affecting 135 people and causing 23 deaths and Quebec City in 2012 affecting over 180 people and causing 14 deaths. Other outbreaks in Moncton New Brunswick and London, Ontario in 2019 were also associated with cooling towers.

The most effective measures to control Legionella risks include actions to reduce survival and growth of the bacteria in building water systems and to reduce opportunities for exposure. Temperature controls, preventing accumulation of stagnant water, adequate disinfection, and regular maintenance and monitoring of water systems can be incorporated into building water management plans to reduce occurrence and improve responses to outbreaks when they occur. It is difficult to say how climate change may impact the occurrence of legionellosis in the future, however increased use of air conditioning systems or rising temperatures in building cold water systems may increase opportunities for Legionella to survive and grow in building water systems, emphasizing the importance of water safety management plans for buildings.

The resources listed here are intended to assist environmental and public health professionals and those responsible for managing water systems in buildings to:

  • Understand the health risks associated with exposure to Legionella bacteria;
  • Understand the factors that can lead to Legionella survival and growth in building water systems;
  • Identify the key approaches to managing Legionella risks in buildings;
  • Understand the steps needed to respond to Legionella outbreaks and the corrective actions required.

Selected External Resources

About Legionella

  • Legionella (Legionnaires’ disease and Pontiac fever) (Centers for Disease Control and Prevention (CDC), 2019)
    This webpage provides a suitable starting point for general information on legionellosis including causes, spread and risks, signs and symptoms, diagnosis, treatment and complications, prevention, and history of the illnesses. Resources specific to clinicianshealth departments and laboratories can also be accessed through this link.
  • Legionellosis fact sheet (World Health Organisation, 2018)
    This fact sheet provides an overview of the causes, symptoms and suggested public health response to legionellosis. The WHO emphasize that addressing the public health threat posed by legionellosis includes prevention measures such as water safety plans in building water systems to control growth of Legionella and dispersion of aerosols.

Managing Legionella in building water systems

  • Legionella quick facts (Public Services and Procurement Canada (PSPC), 2019)
    This fact sheet sets out the five steps for developing a programme to control the growth of Legionella in building water systems applied by PSPC, who operate and maintain a large and diverse portfolio of federal buildings. More detailed information on PSPC’s approach to Legionella control can be found here.
  • Managing Legionella risks in buildings through water safety management planning. (Walkerton Clean Water Centre, 2019)
    These seminar recordings delivered by the Walkerton Clean Water Centre in partnership with public and private sector experts present the key considerations for developing water safety management plans for reducing legionellosis risks in buildings.
  • Turning the Tide: The role of water management to prevent Legionnaires’ disease. (CDC, 2019)
    This webinar recording of the CDC Public Health Grand Rounds from May 2019 includes presentations that examine the connection between Legionella and the built environment, emphasizing the key prevention message that water management programmes can reduce the risk of Legionnaires’ disease and reverse the increase in cases being observed. Approaches to addressing the higher proportion of healthcare acquired cases of legionellosis are discussed.
  • Legionella. Who’s addressing the risks in Canada. (National Research Council of Canada, Health Canada and Public Services and Procurement Canada, 2019)
    This report provides a general overview of Legionella, risk factors, symptoms, and treatment and sets out the roles and responsibilities for managing the risks of Legionella before and during construction of a building, during occupancy and operation of a building and for Legionella case management. This document also lists Provincial and Territorial protocols for Legionella related outbreak prevention, investigation and control.
  • Water quality challenges: Morbidity and mortality associated with building water systems (Environmental Science, Policy & Research Institute, 2018)
    This presentation to the Occupational and Environmental Health Seminar Series outlines challenges in controlling OPPPs including Legionella and key steps for effective building water management. Case studies of different facilities types including healthcare facilities are examined which may be of interest to public health and managers/operators of large or complex buildings.
  • Toolkit: Developing a water management program to reduce Legionella growth and spread in buildings(CDC, 2018)
    This toolkit is a plain language translation of the ASHRAE Standard 188 providing a public health perspective to assist building owners and managers to evaluate whether their buildings require a Legionella water management plan and to identify the necessary process to develop one. The ASHRAE Standard 188 is currently the most widely used industry standard for developing water management programs.
  • Control of Legionella in mechanical systems Standard MD – 15161. (Public Services and Procurement Canada, 2016)
    This document sets out the design, operation, maintenance and testing requirements used by the PSPC to prevent legionellosis in building water systems in federal facilities, which can be adopted by other building managers, maintenance personnel and property owners.

Outbreak investigation and control

  • Legionella (Legionnaires’ and Pontiac Fever) for health departments. (CDC, 2019)
    This webpage sets out a series of resources for public health personnel to prepare for and respond to legionellosis outbreaks including advice, tools, and templates for surveillance, investigation and communication during an outbreak.
  • Management of Legionella in water systems. (National Academies of Sciences Engineering and Medicine, 2019)
    This book developed by the Committee on Management of Legionella in Water System reviews the state of the science regarding Legionella contamination of water systems. The book addresses Legionella growth, transmission, surveillance, prevention & control, and policy with key recommendations.
  • Legionella: questions and answers, 2nd edition. (Public Health Ontario 2019)
    This report lists questions and answers on environmental sampling during a legionellosis outbreak, clinical aspects of an outbreak investigation, infection prevention and control and public health management.
  • Legionellosis Risk Mitigation for Temporary Event Vendors. (NC Department of Health and Human Services, 2019)
    This one-page fact sheet provides specific guidance to vendors at temporary events to reduce the risk of Legionella exposure from displays of hot tubs, displays using outdoor misters or spray cooling equipment and displays with fountains, small water features or display products with water spray.

Peer-reviewed Articles

This list is not intended to be exhaustive. Omission of a resource does not preclude it from having value.


Last updated Jan 07, 2020