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Environmental Protection

Legionella Outbreaks Are Increasing, but Preventable


Chris Boyd

General Manager, Building Water Health, NSF International

We have much to celebrate during World Water Week. Water utilities across the United States provide safe and affordable drinking water throughout the country from large cities to small towns.

However, once water enters distribution systems, many factors can affect its chemical and microbiological composition. These factors can include biofilms, water main breaks, residual disinfectant depletion, stagnant “dead zones” in building plumbing systems, and temperatures that help facilitate growth of certain bacteria, including Legionella, the bacteria responsible for Legionnaires’ disease.

Becoming a crisis

New outbreaks of Legionnaires’ disease, a severe form of pneumonia, are reported across the United States on a regular basis.

The U.S. Centers for Disease Control and Prevention (CDC) reports that more than 8,000 cases were identified in 2018, a fivefold increase since 2000, but public health officials and scientists agree cases are largely underreported or undiagnosed. The Occupational Safety and Health Administration estimates between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease each year in the United States.

A report published Aug. 14 by the National Academies of Science, Engineering, and Medicine estimates 52,000 to 70,000 suffer from Legionnaire’s each year.. The State of Georgia is currently experiencing the largest outbreak in its history.

Risk factors

Legionella is a common bacteria in lakes, rivers, and soil and poses little public health risk in its natural environments. Legionella becomes a significant public health concern when it enters distribution/plumbing systems, where it can multiply and be inhaled in the form of aerosolized droplets from showers, evaporative cooling towers, decorative fountains, and hot tubs, among other water sources.

People over 50, current or former smokers, people with chronic or other underlying diseases, and those with compromised immune systems are at the highest risk of illness. The CDC reports that among the general public, Legionnaires’ disease is deadly in 10 percent of cases, and the mortality rate can rise to 25 percent in healthcare settings. Legionella can also cause the milder Pontiac Fever.


Fortunately, we know that many, if not most, Legionnaires’ disease illnesses and deaths can be prevented. The CDC conducted an exhaustive review of Legionella outbreaks and found approximately 90 percent of them could have been prevented if a comprehensive building water management plan had been implemented.

This conclusion is not surprising to environmental health professionals.

By identifying hazards, developing engineered and process control measures, monitoring outcomes, and validating that the designed approach is working, environmental health professionals can successfully manage risk across a wide range of settings.

This preventative model is routinely applied across the entire environmental health field, in drinking water systems, food processing plants, pharmaceutical manufacturing facilities, restaurants, and even daycare centers, among others. In all these settings, the initial response is to an amplification in risk, not to failures that have led to injury, illness, or death.

Change through policy

In contrast, health departments responding to Legionella outbreaks are frequently not proactive in requesting or even requiring preventative building water management plans. Health departments must shift from a reactive to a preventive model for addressing Legionella outbreaks. To do this, they will need support from legislators and the code officials who write the laws and produce codes that health departments must follow. Specific steps to prevent Legionella illnesses and deaths should include registries for cooling towers for local health departments. Cooling towers are used in air conditioning and refrigeration, and are associated with the majority of community outbreaks, according to a comprehensive review of Legionnaires’ disease outbreaks between 2006 and 2017 published by Kerry A. Hamilton, Charles N. Haas, and Warish Ahmed in the May 2018 journal Current Environmental Health Reports.

Other prevention measures should include legislation that requires water management plans for building owners, as well as surveillance/reporting and updating plumbing codes.

Working in collaboration, the public and private sector can reduce the number of Legionnaires’ disease victims.


Experts from around the world will gather in September at the Legionella Conference 2019 – Building Water Systems: The Sustainability & Public Health Nexus to explore this growing public health concern, to discuss emerging issues related to plumbing systems, and to explore proactive water management strategies.

CDC’s Dr. Pat Breysse, director of the National Center for Environmental Health/Agency for Toxic Substances and Disease Registry, will deliver the opening keynote address on Sept. 11 at the conference hosted by NSF International and the National Environmental Health Association. More information about the conference can be found at

Learn more about Legionella at

Chris Boyd, General Manager, Building Water Health, NSF International, [email protected]

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