Aug. 14, 2019

Stronger Policies Needed to Protect the Public From Legionnaires’ Disease

WASHINGTON – The U.S. needs stronger policies and guidance to combat Legionnaires’ disease, a form of pneumonia caused by inhaling air contaminated with Legionella bacteria from water systems, says a new report from the National Academies of Sciences, Engineering, and Medicine. Currently there is an absence of regulations that can broadly control the presence of Legionella in water systems, the report states.

The report – titled Management of Legionella in Water Systems -- estimates that about 52,000 to 70,000 Americans suffer from Legionnaires’ disease each year, an incidence rate about 10 times higher than the number of reported cases, which do not capture everyone who contracts the disease. Legionnaires’ disease afflicts and kills more people in the U.S. than any other reported waterborne disease. 

Studies worldwide have shown increasing incidence of Legionnaires’ disease. In the United States, the reported incidence of Legionnaires’ disease increased more than fivefold from 2000 to 2017, likely due to multiple issues, including an increasing share of the population with health vulnerabilities (including the elderly and immunosuppressed), more people living in cities served by aging and centralized water systems that include cooling towers, and newer and easier ways to test for the disease, among other factors, the report says.

“A range of approaches can and should be used to better protect the public from Legionella bacteria,” said Joan Rose, chair of the committee that wrote the report, and Homer Nowlin Endowed Chair of Water Research at Michigan State University in East Lansing. “These include ensuring that hot water temperatures in buildings are high enough, requiring a minimum level of disinfectant in public water systems, and offering homeowners more guidance on how to prevent Legionella. We hope our report serves as a road map to help policymakers and others take action.”

Inhaling Legionella can cause either classic Legionnaires’ disease -- marked by fever, cough, shortness of breath, muscle soreness, and sometimes gastrointestinal, neurologic, or mental symptoms – or a milder flu-like condition called Pontiac fever. Between 3 and 33 percent of Legionella infections lead to death; patients are more likely to die from Legionnaires’ disease if they are immunocompromised, receive delayed treatment, or acquire their disease in a hospital.

The Legionella bacteria that cause these illnesses grow inside amoeba that are part of biofilms – thin layers of microbes that coat wet surfaces. For example, biofilms can form in drinking water distribution systems and building plumbing systems and their associated faucets and showerheads, cooling towers, hot tubs, and fountains. Conditions that promote the growth of biofilms and Legionella include warm temperatures, stagnant water, lack of chemical disinfectants, and the presence of nutrients in the water because of pipe corrosion.

The federal Safe Drinking Water Act (SDWA) does not provide any substantial control of Legionella in water systems, the report says.  Although the SDWA requires that public water supplies be treated with disinfectants to kill microbes, the disinfectant may not extend into building plumbing downstream of treated public water systems, which leaves these buildings vulnerable to Legionella growth. Two federal agencies, along with New York City and New York State, have attempted to control Legionella in certain buildings and cooling towers under their purview, but most buildings and private residences are not protected by regulations.  Building and plumbing codes were not written to control Legionella, although they could be modified to do so. 

More uniform protection of public health is needed from Legionella in building water systems, including hospitals and healthcare facilities, and cooling towers across the country, the report says. It calls for a range of actions to combat the growth of the bacteria, including the following:

In addition, education about how to monitor, prevent, and control Legionella is needed for those designing water systems, overseeing municipal water supplies, developing and implementing plumbing codes, as well as for those in government responsible for the safety of buildings, cooling towers, and water supply. And well-funded studies in multiple jurisdictions are needed to determine the most common sources of sporadic Legionnaires’ disease, which is critical to reducing the rising rates observed over the last 20 years.

The study — undertaken by the Committee on Management of Legionella in Water Systems — was sponsored by the Centers for Disease Control and Prevention, U.S. Department of Veterans Affairs, U.S. Environmental Protection Agency, and the Alfred P. Sloan Foundation. The National Academies are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit  

Sara Frueh, Senior Media Officer

Office of News and Public Information
202-334-2138; e-mail

Additional Resources:

Interactive Overview of Legionella in Water Systems