Legionella

[Last Updated: Feb 24, 2021]

Legionella bacteria are opportunistic premise plumbing pathogens (OPPP) that can cause illnesses collectively referred to as legionellosis. Legionellosis includes Pontiac fever, extrapulmonary legionellosis 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 waterborne 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 Legionella contaminated water droplets or aerosols into the lungs. When contaminated water in cooling towers, shower heads, decorative fountains, hot tubs, flushed toilets, 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 contaminated by Legionella, followed by aspiration of the bacteria into the lungs. Some of the symptoms of Legionnaires’ diseases are similar to those experienced due to COVID-19 infection, which has raised concerns about the need to maintain surveillance for possible cases of legionellosis during the pandemic. (See more from the NCCEH on Building shutdown and re-opening during the COVID-19 pandemic).

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 1.02 between 2010 and 2018. In 2018 there were over 600 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 source of infection can be difficult to trace as shown with a cluster of six cases in New Westminster, B.C., and seven cases in Montreal, Quebec, both in September 2020, for which the possible sources of infection are still under investigation.

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. Increased use of air conditioning systems or rising ambient temperatures in a building’s cold-water systems may increase opportunities for Legionella to survive and grow in those systems. This emphasizes the importance of regular monitoring and having water safety management plans in place 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 and Legionnaires’ disease (legionellosis) (Walkerton Clean Water Centre, 2020)
  This resource collection includes a broad range of information on legionellosis, prevention of Legionella exposure through effective water management, sampling, standards, surveillance, and outbreak investigations.
   
• 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 clinicians, health 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

• Toolkit for controlling Legionella in common sources of exposure (CDC, 2021)
  This toolkit provides actionable information for public health and building owners and managers to control Legionella in common sources of disease outbreaks including potable water systems, cooling towers, hot tubs, decorative water features. Advice for other devices that contain non-sterile water such as irrigation systems, fire suppression systems, safety showers, ice machines, humidifiers etc. is also provided.

• 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.

• Legionnaires’ disease from water systems left idle during the COVID-19 pandemic (Worksafe BC, 2020).
  This risk advisory sets out potential sources of Legionella exposure in the workplace, and steps to reduce risks arising from idle water systems.
   
• Public water system characteristics that may affect Legionella occurrence in building water systems. (US EPA, 2020)
  This webinar recording from the US EPA highlights public health impacts and challenges to managing Legionella in drinking water, and potential risk factors in public water supplies including inadequate disinfectant residual, high water age, nutrient availability, corrosion, and poor pipework condition.
   
• 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.
   
• Residential hot tubs and pools: Safe water quality (Health Link BC, Feb 2018)
  This fact sheet outlines some key tips for achieving and maintaining disinfection in a hot tub or pool to prevent exposure to bacteria such as Legionella.
   
• Preventing Legionnaires’ disease: A training on Legionella water management programs (PreventLD Training) (US CDC and partners, 2018)
  This free online training course is designed to assist public health professionals, building managers and others involved in supply of clean drinking water to understand the steps involved in assessing Legionella hazards and developing a Legionella management program.

Outbreak investigation and control

• Strategies to combat Legionnaires’ disease. Outbreak investigation and preventive policy. (NCCEH, 2020)
  This webinar recording includes a presentation from Fraser Health Authority on a Legionnaires’ disease outbreak investigation associated with cooling towers in Surrey, BC and a presentation from City of Vancouver on the implementation of a registry for cooling towers and decorative water features in the city to assist health authorities with outbreak investigations.
   
• Mixed community and nosocomial outbreak of Legionella pneumophila in Montreal Quebec in 2019. (Cadieux et al. 2020)
  This report describes the investigation of a community-based outbreak of Legionella in Montreal Quebec in 2019 that resulted in 14 cases, including cases in a retirement home and an acute care hospital, which were linked with typing of clinical isolates suggesting a common environmental source.
   
• 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.
   
• Legionnaires’ disease at temporary events or trade shows – A guide for event coordinators & vendors (Vancouver Coastal Health, 2020)
  This fact sheet provides guidance for vendors at temporary events to reduce the risk of Legionella exposure from displays of hot tubs, cooling equipment (e.g., misters), decorative water features or plumbing fixtures (e.g., shower heads). 
   
• Legionella outbreak investigation and control (BC Centre for Disease Control, 2018)
  This guidance document provides evidence-based approaches to investigation and management of cases and outbreaks of legionellosis in BC to support public health professionals.
   
• Legionellosis: Key considerations for case and environmental exposure investigation. (Public Health Ontario, 2017)
  These presentation slides examine Ontario’s case incidence from 2010 to 2017 and detail the approach to legionellosis investigation used in Ontario.
   
• Sampling/environmental assessment videos (CDC, 2015)
  This collection of instructional videos provides an overview of premise plumbing and water fixtures, and advice on how to sample taps, cooling towers, hot tubs (spas) and fountains during a legionellosis cluster or outbreak investigation.
• Canadian jurisdictions with regulations for building water systems to control Legionella:
  • City of Hamilton, Ontario
  • Province of Quebec
  • City of Vancouver, B.C.
  • Federal buildings managed by Public Service and Procurement Canada (standard MD-15161)

Peer-reviewed Articles

• LegionellaDB – A database on Legionella outbreaks (Gonçalves et al., 2021)
  This article introduces the LegionellaDB database developed from metadata analysis of peer-reviewed papers reporting on Legionella outbreaks from around the world. The database allows users to search for information on outbreaks by location, number of cases, setting and identified source of the outbreak.
   
• Living with Legionella and other waterborne pathogens. (Falkinham 2020)
  This review article summarises characteristics of Legionella spp and other opportunistic plumbing pathogens, their occurrence in premise plumbing, pathways of transmission, monitoring and remediation.
   
• Transmission of Legionnaires’ disease through toilet flushing. (Couturier et al. 2020)
  This article reports on an investigation of Legionnaires’ disease in two patients who used the same hospital room five months apart. Toilet flushing was identified as a likely transmission route, causing aerosolization of Legionella contaminated water.
   
• Did municipal water distribution system deficiencies contribute to a Legionnaires’ disease outbreak in Quincy, IL? (Rhoads et al. 2020).
  This article reports on a Legionnaires’ disease outbreak in Quincy, IL, 2015, which identified changes to the municipal drinking water supply disinfectant and corrosion control practices, which may have influenced the conditions for Legionella growth in the distribution system.
   
• Legionella risk in evaporative cooling systems and underlying causes of associated breaches in health and safety compliance. (Crook et al. 2020).
  This article reports on data from the UK on Legionella associated infections and deaths linked to industrial cooling towers and identifies key failings in training, maintenance, risk assessment and written control schemes. 
   
• Critical review: propensity of premise plumbing pipe materials to enhance or diminish growth of Legionella and other opportunistic pathogens (Cullom et al. 2020)
  This review article sets out the influence of different premise plumbing materials (metals, plastics etc.), condition, and design on the growth of OPPPs in buildings.
   
• Legionnaires’ Disease Cases at a Large Community Hospital – Common and Underdiagnosed (Spiegelman et al., 2020)
  This article presents the results of a study to examine the frequency of Legionnaires’ disease in cases of pneumonia hospitalizations in Toronto in summer of 2018, highlighting that cases of Legionnaires’ disease are underdiagnosed.
   
• Legionella regulation, cooling tower positivity and water quality in the Quebec context. (Racine et al., 2019)
  This article examines Legionella and water quality data from Quebec cooling towers between 2014 and 2017 following the introduction of new regulations in 2014 in response to a significant outbreak in 2012.
   
• Outbreaks of Legionnaires’ Disease and Pontiac Fever 2006–2017(Hamilton et al., 2018)
  This article reviews outbreaks of legionellosis around the world between 2006 and 2017 and examines the specific building water systems and fixtures implicated or suspected as the source of outbreaks.
   
• The influence of climate change on waterborne disease and Legionella: a review. (Walker, 2018)
  This review article examines the possible influence of climate related factors such as temperature, rainfall intensity, rainfall duration and drought on the incidence of legionellosis.
   
• Legionella: a re-emerging pathogen. (Herwaldt and Marra, 2018).
  The review article summarizes recent knowledge about Legionella epidemiology, clinical characteristics, outbreaks, epidemiology, detection, prevention and treatments.
   
• Legionellosis following water birth in a hot tub in a Canadian neonate (Barton et al., 2017)
  This article reviews of a case of legionellosis in a newborn following a water birth. Although cases of legionellosis are most often found in adults over the age of 50, this case highlights the possible need to consider Legionella testing in younger patients in some circumstances.
   
• Legionnaires’ disease outbreaks and cooling towers, New York City, New York, USA. (Fitzhenry et al., 2017)
  This article reviews six Legionnaires’ disease outbreaks in New York City between 2006 and 2015, and the evolution of detection and response actions, including improved cluster detection, laboratory capacity, identification of cooling towers and experience amongst investigation teams.
   
• Current and emerging Legionella diagnostics for laboratory and outbreak investigations. (Mercante and Winchell, 2015)
  This review article outlines the physiology and ecology of Legionella, examines current methods of detection and diagnosis and advances in the field, and discusses current challenges for healthcare, building managers and public health in combating legionellosis.

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