Find out what this national report says buildings should do to prevent Legionnaires’ disease

by Brianna Crandall — August 26, 2019 — 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 — private, nonprofit institutions that provide independent, objective analysis and advice to inform public policy decisions. 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 reportedly do not capture everyone who contracts the disease. Legionnaires’ disease afflicts and kills more people in the US than any other reported waterborne disease.

Legionnaire’s disease graphic from NASEM

Legionnaire’s disease graphic courtesy NASEM. Click image to enlarge.

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.

Joan Rose, chair of the committee that wrote the report, and the Homer Nowlin Endowed Chair of Water Research at Michigan State University in East Lansing, stated:

A range of approaches can and should be used to better protect the public from Legionella bacteria. 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 health-care 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:

  • For all types of buildings, hot-water heater temperatures should be maintained above 140°F (60°C) and the hot-water temperature to distal points (the point of connection to a fixture such as a faucet, showerhead, or thermal mixing valve that blends hot and cold water right before they reach the tap) should exceed 131°F (55°C).  Maintaining water temperature outside Legionella’s preferred growth range is the main Legionella control strategy, and it has been proved successful by multiple field studies. These temperature requirements could be codified by changing building and plumbing codes for residences and other buildings or by modifying the Centers for Medicare and Medicaid Services (CMS) memo that affects health-care facilities.
  • Guidance is needed for homeowners about practical steps that can be taken to combat Legionella bacteria. For example, flushing stagnant water from taps after periods of disuse may help to prevent Legionella Increasing the water temperature in household hot-water heaters to 140°F (60°C) also can help limit Legionella growth in home hot-water systems, but this step must be weighed individually against the risk of scalding and burns.
  • All public buildings such as hotels, businesses, schools, apartments, and government buildings should be required to have a water management plan. ASHRAE 188, AIHA (2015), and other guidance documents are available to help create a water management plan that can meet this requirement. Ideally, this requirement would be codified by either local jurisdictions with authority (such as building inspectors) or state authorities (such as departments of environmental protection or health). Once codified, this requirement could be enforced by insurance companies; i.e., without a water management plan, a building would not qualify for insurance.
  • Low-flow fixtures should not be allowed in hospitals and long-term care facilities, due to these buildings’ high-risk occupant populations. Low-flow fixtures have been promoted to conserve water and sometimes energy, but these fixtures increase water stagnation and reduce disinfectant levels, presenting a greater risk for Legionella.
  • Criteria for certifying green buildings, energy-conserving features, and water conservation features should be modified to take into account risk factors for growth of Legionella in building water systems. Green buildings have exacerbated problems with Legionella by lowering hot-water temperatures and by lengthening the amount of time water sits in pipes, which leads to a decrease in disinfectant and associated biofilm growth. Substantial water conservation can still be potentially achieved while protecting public health if the water is more deliberately managed to prevent stagnation — for example, through routine flushing of a target fraction of the water use.
  • Cooling towers should be registered and monitored. Building- and industrial-scale cooling towers — which remove heat from recirculating water used in water-cooled chillers, heat pumps, and other HVAC equipment — have been implicated in many outbreaks of Legionnaires’ disease. These towers may generate bacteria-laden aerosols that drift away from the facility and then are inhaled by people working and living in the building or by passersby. Cooling tower registries allow for rapid public health response to community clusters of Legionella cases, including timely remediation of sources of infection.
  • A minimum disinfectant level should be required throughout public water systems, along with monitoring for Legionella. EPA should require a minimum level of disinfectant in public water systems and validate that the treatment is working by routine monitoring for Legionella. Monitoring could focus on warm-water conditions and be triggered when water temperatures consistently exceed 20°C.

In addition, education about how to monitor, prevent, and control Legionella is needed for those designing water systems, overseeing municipal water supplies, and 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 full Management of Legionella in Water Systems report — undertaken by the Committee on Management of Legionella in Water Systems — was sponsored by the US Centers for Disease Control and Prevention (CDC), US Department of Veterans Affairs (VA), US Environmental Protection Agency (EPA), and the Alfred P. Sloan Foundation, and is available as a free PDF download from the National Academies website.

A recording of the report release briefing is available online. Presenters’ slides (PDF) have also been posted.

The American Industrial Hygiene Association (AIHA) guideline Recognition, Evaluation, and Control of Legionella in Building Water Systems, which is referenced by the National Academies report,  is available for purchase in the AIHA Marketplace. An article in the June/July issue of The Synergist discussed Legionella regulations in New York.