Today marks 50 years since approximately 4,000 Legionnaires arrived at the Bellevue-Stratford Hotel in Philadelphia to kick off the 58th annual convention of the American Legion’s Pennsylvania Chapter, not knowing that many of them would contract a deadly illness while there.
This article outlines some key milestones in the history of Legionella preventive efforts and – based on lessons learned – proposes key factors for reducing Legionella in the years ahead.
Discovery of Legionnaires’ Disease and Legionella
The outbreak of what became known as “Legionnaires’ disease” struck 221 persons, 72 of whom did not attend the convention but were in or near the Bellevue-Stratford Hotel over the same period. 34 died (Fraser 1976).
Then started one of the largest epidemic investigations up to that point in history. After about six months, the Centers for Disease Control and Prevention (CDC) investigators traced the illness, which had been named “Legionnaires’ disease” by the press, to a previously unknown bacterium now called Legionella.
Legionella had secretly been causing disease for a long time, probably since the invention of enclosed plumbing systems. The first known hospital outbreak occurred in 1965 when 81 patients at St. Elizabeths Hospital in Washington, DC developed pneumonia and 14 died. The cause could not be found at the time, but 12 years later, after Legionella was discovered, frozen specimens that had been retained from the outbreak were removed from storage and retested. The results confirmed that Legionella was the cause (Brundrett 1978, Goetz 1991, Thacker 1978).
Key Milestones in Legionella Prevention Efforts in the United States
After the 1977 discovery, tremendous amounts of research ensued to find out why water systems promote growth of Legionella and how the bacteria are transmitted to people’s lungs.
By the 1990s, well over 100 scientific papers had been released, as well as publications (OSHA 1996; Freije 1996) that condensed scientific findings into action steps building operators could implement to reduce risk. Government regulations for Legionella prevention were established in the UK and in some Australian states in 1991.
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Guideline 12 was first published in 2000. Significantly, the CDC, which up to then had recommended a largely reactive approach to Legionnaires’ disease, wrote that, “Adoption of the ASHRAE guidelines could dramatically reduce the likelihood that Legionella will be amplified in a water system, thereby diminishing the risk of transmission” (Fields 2002).
Among the most important Legionella guidelines and standards in the United States, ASHRAE Standard 188 is definitely king. The June 2015 release of ASHRAE 188 was a giant step for Legionella prevention in the United States in part because it represented unprecedented agreement among government agencies and industry groups—not only about the need for Legionella prevention in building water systems—but also about the approach to it.
In recent years, new standards have significantly increased requirements related to water management programs. For example, ASHRAE 514, which became an ANSI standard in July 2023, significantly broadened the scope and increased the level of detail for water management programs. The stated purpose of ASHRAE 188 is to reduce one illness (legionellosis) by managing only one hazard (Legionella) in building water systems. By contrast, the stated purpose of ASHRAE 514 is to “reduce illness and injury from physical, chemical, and microbial hazards,” expanding the scope from one microbe to an unspecified number of microbes as well as to physical hazards (scalding) and chemical hazards.
Factors that will Determine the Future of Legionnaires’ Disease
Although more research is needed to know how better to prevent Legionnaires’ disease, evidence indicates that the reason Legionnaires’ cases have been on the rise since ASHRAE 188 was released is not due to lack of knowledge, but lack of action by building owners.
Our 2021 study of more than 900 water management programs clearly showed that the premise of ASHRAE 188 is sound – fully implementing a comprehensive water management program will reduce Legionella in water systems. The problem is that very few facilities are doing so. The CDC found that 70% of the deficiencies implicated in Legionnaires’ outbreaks from 2015 to 2019 were in WMP implementation.
Most hospitals are required to implement water management programs (WMPs) either by law or by their accrediting organization, but very few non-healthcare facilities that should be implementing WMPs based on ASHRAE 188 even have one. State health departments realize this, and some are working on adopting regulations. States indeed hold the keys to preventing Legionella infections.
New Jersey’s regulations, effective later this year, require Legionella water management programs for all building types and water systems per ASHRAE 188. Since 2015, other states have established regulations but only for specific types of water systems (cooling towers) or only for healthcare facilities.
All eyes are on New Jersey and other states to see if they succeed. Whether cases of Legionnaires’ disease in the US continue to rise or are drastically reduced depends on states establishing smart regulations – and inspecting WMPs well.
What do you think are key milestones in the history of Legionella preventive efforts and key factors for reducing Legionella in the years ahead?
Thanks Matt, a really thoughtful article.
I recall my first job in the industry at 17 years old in 1993 when my new boss gave me a copy of HSG 70 and said this is your new bible, read it and learn it. Great advice as I made a career from that day.
For me, the future has to be in the design of buildings water systems and embracing new technologies at design stage. Already we are seeing cooling of recirculated domestic cold water in healthcare settings with high risk augmented patients (rare in the UK but I have seen at least one in a recent build).
It is also still rare to see dry tested fittings specified (such as taps and healthcare specific thermostatic taps and fittings) so I would like to see that being the norm for all water fittings.
Finally, the future design of drainage systems (not specifically for Legionella control) must be improved. I see a huge shift in gravity systems being replaced with vacuum systems in the distant future.
All the best from the UK!
Thank you Haydn! Great point about the importance of plumbing system design.
Key factors for reducing Legionella risks in the future, is that it becomes mandatory by law for building owners to implement a WMP. Unless it is mandatory, it will only be implemented in health care facilities and sensible industries, where it pays off, due to production issues.
It makes little sense, just to fucus on Legionella. It is better to focus on the general hygiene in the water system. The good thing is, whatever you do do prevent Legionella, also helps against most other microbes.
ASHRAE 188 is great, but too specific on Legionella. On the other hand ASHRAE 514, is too broad and should be sharpened in the future.
In Europe different standards are used, e.g. L8, VDI 6022 and ISO 22.000, and like ASHRAE 188 and 514 they all recommend to build and implement a WMP according to HACCP principles. Verification and documentation are the most important part of any WSP – and the resposibility needs to be clearly defined, but also limited to what can be measured.
Thank you for the thoughtful comments, Leo. All the best to you!
ASHRAE188 and its evolution to ASHRAE514 as well as well-designed Water Management Program platforms, are significant milestones in the history of Legionella prevention.
There is a wealth of knowledge and years of practical experience available to us from those that have been involved with managing and minimizing these risks over the decades. Let’s continue to tap into these resources and mentor together for as long as we can.
We need to also review and enhance plumbing standards and codes to minimize low flow and stagnation in premise plumbing systems and associated unit operations in health care and commercial applications. These last two will remain key factors to minimizing water borne pathogen risk, exposure to physical, chemical, and microbial hazards, and thereby reducing Legionella in the future. [Please excuse any typos]
Great points, Anthony. I agree that plumbing codes are important. Thank you for commenting.
Thank you, the article is clearly and interestingly written. I think that in the future, regulation will emphasize disinfection of the end point. It is not logical and effective to invest so much in the water system when a significant part of the problem is created at the end point. Until now, it was not possible to disinfect the last meter, but my invention, fortunately, makes this possible.
Thanks for you input, Lidor.
Thank you, Matt. I am glad you included a link to your 1996 publication Legionella Control in Healthcare Facilities because, as far as I am concerned, that was certainly an early and key milestone in legionellosis prevention.
It’s good to hear from you, Dan! Thank you for the encouraging comment.
Thank you sharing this insightful information Matt.
Looking ahead, it is believed the most important factors for further reducing Legionella risk will be:
• Having a government mandated adoption of comprehensive water management plans, supported by strong governance, accountability and utilizing the skills of water safety professions.
• Better building and water system design, with greater emphasis on minimizing stagnation, maintaining appropriate temperatures, and ensuring effective disinfectant residuals.
• Education and training for facility managers, engineers, healthcare operators, infection preventionists and building owners to ensure consistent implementation of best practices and having a more streamlined, uniform set of guidelines that are less subjective and more concise to that more facilities can follow a standardized approach.
• Adaptation to emerging challenges, such as aging infrastructure, water conservation measures, and climate-related changes that may increase Legionella growth opportunities.
• Adopting a multibarrier approach with a cross functional team to help adopt s strategy that can be shared across departments.
Ultimately, the greatest progress will likely come from moving beyond periodic testing toward a proactive, risk-based approach that integrates design, operations, monitoring, and continuous improvement across the entire water system lifecycle.
Thanks for taking the time to write well thought-out comments, Amanda.
Matt,
Congratulations on an excellent historical summary. I see several major factors contributing to the increasing frequency of isolated infections and outbreaks.
They are:
The impact of poor plumbing design with respect to pipe sizing, valve and fixture selection, and balancing This leads to problems with water velocity, unintentional dead legs, water temperature control, extended water age and deposit accumulation.
The impact of poor post construction cleaning,
passivation and monitoring on new construction.
The stubborn impact of the Covid pandemic on building occupancy. Buildings and plumbing systems are designed assuming occupancy projections. Low occupancy promotes low water usage, low flow, low velocity, poor temperature control, extended water ageand deposits.
The impact of environmental regulation on the use of historically very effective chemical treatment programs. This has a “triple whammy” effect on corrosion, deposition, and microbial multiplication.
The inconsistency and the inadequacy of regulations from state to state, combined with the above factors, leading to reluctance on the part of building owners to implement basic treatment and control strategies.
What can we do about this mix of influences?
I. suggest the following preliminary ideas:
Require those who design our plumbing systems to be given additional plumbing specific training and to be licensed specifically for plumbing design.
Develop and require a specific standard and specific education for new construction cleaning and passivation.
Require specific building shutdown ,start-up and low occupancy monitoring, cleaning, and treatment practices.
Increase training for water treatment vendors and building operators on. the need for better monitoring and control of the operation and treatment of building water systems, including the application of treatment to the incoming water supplies if municipal pretreatment is insufficient.
Establish uniform and complete regulations to require the above to be consistently applied, monitored and recorded.
Regards,
Bob Cunningham
I know your comments are based on many years of experience, Bob. Thank you for taking the time to write out the factors and recommendations. And thank you for all you have contributed to the water treatment industry and to Legionella prevention.
Good article – but as mentioned also in comments, ‘new’ technology is very effective. If you don’t make a point to learn – and try new techniques, you get what you’ve always got. It’s very difficult to access leaders who have the capacity – and authority to assign and execute a valid and true pilot. And, consider the tech I’m aware of that is highly effective vs. waterborne pathogens – consistently and durably is ‘Clean&Green – and 35+ years in the global market. Regardless, it won’t take long to dramatically reduce legionella occurrences. I hope!
Thanks for your input, Bob
As of today, ASHRAE Standard 514 is not mandated by either California or Nevada as a statewide code or regulation. It remains a consensus standard that organizations may voluntarily adopt or may be required to follow by contract, accreditation, or an Authority Having Jurisdiction (AHJ), but it has not been incorporated into either state’s building or plumbing codes.
California has not adopted ASHRAE 514 into:
California Building Standards Code (Title 24)
California Plumbing Code
California Mechanical Code
California Drinking Water regulations
The 2025 Title 24 codes (effective January 1, 2026) include healthcare-related plumbing provisions addressing topics such as potable water disinfection, hot-water temperatures, storage tanks, and Legionella control, but they do not adopt ASHRAE 514 as an enforceable standard.
Healthcare facilities in California are still generally expected to develop Legionella Water Management Programs consistent with ASHRAE 188 because of CMS expectations and accreditation requirements—not because ASHRAE 514 has been adopted into California law.
Nevada likewise has not adopted ASHRAE 514 into its statewide building codes.
Nevada’s current statewide building code references include standards such as ASHRAE 90.1 for energy efficiency, but not ASHRAE 514 for building water risk management.
When ASHRAE 514 May Still Apply
Even though it is not state law, ASHRAE 514 may effectively become a project requirement through:
Hospital or healthcare system policies
VA or federal facility design criteria
Owner specifications
Insurance risk-management requirements
Accreditation organizations
Contract documents
Local AHJ requirements on a case-by-case basis
Mike, thanks for commenting about ASHRAE 188 and 514 adoption.