Puzzled by® Legionella?

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Get the ultimate Legionella resource and study guide written by Legionella expert, Dr. Janet E. Stout. Developed to help prepare for the ASSE 12080 certification exam, and for any professional concerned with water safety.

9 Intuitive Modules

Explore an excerpt from each module.


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Introduction and Overall Learning Goals

Legionnaires’ disease is a severe infection caused by Legionella bacteria that affects more than 10,000 people in the United States every year, with 10% of those people dying from the disease. The goal of this guide is to educate professionals involved with water safety and management programs, including infection preventionists, risk management professionals, public health professionals, safety officers, facility managers, engineering and maintenance staff, water treatment professionals, and consultants. Through the education and training provided in this guide, we hope to reduce the risk of Legionnaires’ disease in facilities.

Module 1: What is Legionnaires' Disease?

Since 1976, outbreaks of Legionnaires’ disease continue to occur and increase each year. Between 2000 and 2017, there was an increase of five and a half times the number of cases reported (Centers for Disease Control and Prevention 2018). This increase could be due to improved awareness of Legionnaires’ disease and an increased demand for patient testing. It could also be a result of an increase of Legionella bacteria in our environment, due to weather events, or a greater number of susceptible people in the general population, such as the elderly and immunocompromised…

Module 2: Proactive Prevention and Testing for Legionella in Water Systems

The presence of Legionella in the water systems of hospitals and other buildings is the most important risk factor for healthcare or building-associated Legionnaires’ disease. You may find it surprising that the CDC doesn’t offer recommendations for routine Legionella testing outside of case investigations—even for hospitals. This is despite the fact that testing has led to the discovery and prevention of healthcare-associated Legionnaires’ disease. Instead, the CDC requires testing the water only after cases have been identified as part of an investigation.

Module 3: How Can Legionella Infections Be Prevented?

ASHRAE Standard 188 provides a description of the types of buildings and water devices that are included in a water safety and management plan, the steps to maintain a water safety and management plan, and who should be included on a water safety and management team. It also describes the types of environmental conditions that promote Legionella growth.

Although ASHRAE 188 recommendations are voluntary, the standard provides local authorities with the information required to develop plumbing codes to help prevent Legionella growth…

Module 4: Legionella Risk Assessments

It’s important that your water safety and management team develops a sampling and monitoring plan. The sampling and monitoring plan describes when and where water samples are collected for Legionella and how water is monitored to ensure that conditions to limit Legionella growth are maintained.

There are several steps to creating a sampling and monitoring plan. The first step is to review plumbing drawings and floor plans for areas where Legionella growth might occur. Your water safety and management team should review the type…


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Module 5: Water Safety and Management Plans

Water safety and management plans are designed to manage your building’s water systems to minimize the risk of building-associated Legionnaires’ disease. Simply put, their purpose is to prevent Legionella from growing in your building’s water systems. This can be accomplished through monitoring and controlling water conditions that degrade water quality and promote Legionella growth. When designed and implemented effectively, these plans can minimize Legionella growth and the potential for disease transmission.  

CMS requires that all licensed hospitals, critical access hospitals, and long-term care facilities implement a water safety and management plan. 

Module 6: Water Treatment and Disinfection

Implementing supplemental disinfection and ensuring disinfection systems are properly functioning enable you to control Legionella growth. If the water system is working as it should, but a significant amount of Legionella has been detected and it is a pathogenic species or serogroup, then you should consider a supplemental disinfection method. This is especially true if your facility houses people that are susceptible to Legionellosis, such as a senior living or a healthcare facility.

Module 7: Preventing Legionnaires’ Disease During Construction and Renovation

Similarly, a disturbance in potable water served as the source of Legionella exposure during construction at the Rhode Island Hospital in Providence. In this case, there were three separate outbreaks of Legionnaires’ disease that occurred over the course of 10 years, resulting in two deaths (Mermel et al. 1995). When testing was performed, it showed widespread contamination of the hospital’s potable water system with Legionella pneumophila serogroup 1. Investigators matched an increase in positivity to a concurrent construction event…


Module 8: Legionella Outbreak Response

When a health department determines that an investigation is required, public health officials work with facility leadership, including facility managers, hospital administrators, quality assurance staff, infection preventionists, and others. If your facility is found to be the source of exposure for a Legionnaires’ disease case, emergency prevention measures might need to be implemented.

The following emergency prevention measures could be required to protect building occupants and patients from exposure to Legionella, and to identify the extent of the outbreak and source of exposure (CDC 2019)…

Module 9: Other Waterborne Pathogens

he opportunistic waterborne pathogens discussed in this module are microorganisms specifically mentioned in the 2018 Centers for Medicare & Medicaid Services (CMS) memorandum (Wright 2018), which mandated addressing the risk from waterborne pathogens in building water systems (as discussed in Module 3). These microbes include: Pseudomonas, Acinetobacter, Burkholderia, Stenotrophomonas, nontuberculous Mycobacteria (NTM), and fungi. 

Unlike the fecal pathogens mentioned earlier, these organisms cannot be completely removed from water or inactivated by filtration or disinfection at the treatment plant. At times, opportunistic waterborne pathogens can amplify after these treatments…

Take a peek inside

Flip through to preview the introduction spread from each module.


Ideal for Professionals

concerned about water safety, instructors, and students.

Authoritative Resource & Guide

provides foundational knowledge you need to understand and control Legionella to prevent Legionnaires’ disease.

Written by The Legionella Experts®

with contributions from infectious disease, microbiology, engineering, public health, and infection prevention professionals.

Officially Recognized by ASSE

as appropriate training material in preparing for the ASSE 12080 certification examination.

Accessible & Practical

filled with tips and myth-facts.


Take practice quizzes, access videos and download PDFs, web resources and tools.


“Easy to read and engaging. Love the QR codes and myth facts.”

“Very informative and easy to follow. Information was clear cut.”

“This guidebook is the perfect reference to help control Legionella.”

Fundamental Diagrams

Our diagrams featured throughout the study guide enhance the learning and the cognitive processing of the reader. We took conceptual information and turned it into an easy to understand visual representation that proves to be far more effective in information retention.

Interactive Quizes

Each module ends with an engaging quiz to make sure you’re well on your way to becoming a Legionella expert professional. The book author has strategically created these quizzes to help you retain the most crucial informaiton for the topic.

Use the easy to scan QR codes in to take the quiz online or simply answer in the study guide itself.

Myth vs. Fact

We’re setting the record straight with Legionella. Don’t be fooled by the rumors floating around. Our experts have developed a Myth vs. Fact figure for each module to address the most common, but sometimes detrimental misunderstandings.

About the author

Dr. Janet E. Stout is internationally recognized for pioneering discoveries and research and in Legionella detection, control and prevention. An infectious disease microbiologist for more than 30 years, her expertise includes disinfection and control strategies for the prevention of Legionnaires’ disease and other waterborne pathogens. Her seminal discovery that demonstrated the link between the presence of Legionella in hospital water systems and Legionnaires’ disease shifted the paradigm from cooling towers to water distributions systems as the primary source for Legionnaires’ disease. Published in the New England Journal of Medicine in 1982, Dr. Stout’s findings changed the direction of research and expanded the water treatment industry’s approach to controlling Legionella. To date, Dr. Stout has evaluated every major Legionella disinfection technology used in the industry. Her work is published widely in major medical and scientific peer-reviewed journals.

Dr. Janet E. Stout

Founder, Special Pathogens Technology
Founder, Special Pathogens Laboratory

Associate Research Professor, University of Pittsburgh Swanson School of Engineering

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Legionella Resources

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Legionella prevention solutions through education and evidence-based water management technology.