5 NASEM Report Recommendations for Better Legionella Control

"Legionella is now the number one cause of reported waterborne disease in the United States," wrote Joan Rose, Michigan State University water microbiologist and chair of NASEM's committee for the report, in the preface. "Legionella pneumophila is the species most often diagnosed as the cause of Legionnaires' disease. For every case associated with an outbreak, there are nine more sporadic cases."

Given the complex issues associated with controlling the bacteria and a lack of clear federal guidelines, the Centers for Disease Control and Prevention, the Department of Veterans Affairs, the Environmental Protection Agency (EPA), and the Alfred P. Sloan Foundation asked NASEM to examine the current state of Legionella science.

NASEM's committee undertook a two-year study, during which they reviewed scientific literature, listened to international experts, looked at rules for addressing Legionella contamination, and conducted original data analyses. The resulting prepublication report released in 2019 calls for stronger policies. Specifically, the chapter about regulations and guidelines on Legionella control in water systems features five recommendations.

1. Expand the CMS Memorandum to Require Monitoring for Legionella in Environmental Water Samples

In 2017, the Centers for Medicare & Medicaid Services (CMS) issued a memorandum requiring hospitals and long-term care facilities that receive CMS funding to develop and implement water management plans. The memo targets buildings where the Legionnaires' disease mortality rates are high due to vulnerable patient populations.

"Routine quantitative Legionella monitoring programs would enable these institutions to assess the effectiveness of their water management programs," the NASEM publication notes. "All health care organizations should have the capacity and expertise to use these data proactively to help limit nosocomial legionellosis."

2. Register and Monitor Cooling Towers

Cooling towers can be hot spots for Legionella bacteria growth and exposure. "Unless the location of cooling towers is known, it is impossible to react quickly to identify the source of an outbreak or to assess the overall contribution of cooling towers to the occurrence of Legionnaires' disease," wrote NASEM's committee. Cooling tower registries enable a rapid response to clusters.

Monitoring cooling towers, meanwhile, can help with disease prevention. Citing examples from Quebec and Garland, Texas, NASEM found that regulations requiring ongoing Legionella monitoring of cooling towers have been shown to reduce colonization rates in them.

3. Require Water Management Plans for All Public Buildings

The most prominent guiding documents for managing Legionella in building water systems — including the ASHRAE 188 standard, 2015 direction from the American Industrial Hygiene Association, and National Sanitation Foundation International's standard 453 — require developing a water management plan or program to mitigate risks. The NASEM committee recommends that these plans become a requirement for all public buildings. This would extend to hotels, businesses, schools, apartments, and government buildings.

"Ideally, this requirement would be codified by either local jurisdictions with authority or state authorities," the report says. "Once codified, the requirements could be supported by insurance companies; that is, without a water management plan, a building would not qualify for insurance."

4. Require a Temperature of 60 C (140 F) for Hot Water Heaters and 55 C (131 F) to Distal Points

NASEM found international consensus for maintaining minimum temperatures across the different parts of a hot water system to restrict Legionella growth, even when a disinfectant is used. Making sure that requirement is met means measuring the temperature at hot water systems' distal points.

"Typically, the requirements include maintaining temperatures of greater than 60 C (140 F) at the water heater and in reservoirs, greater than 55 C (131 F) in the return loop, and ensuring that distal points reach a minimum temperature of 55 C within one minute of use," the publication says. A chapter about strategies for building water systems discusses lowering the risk of scalding.

Periodic monitoring of Legionella and water system temperatures is mandatory in England, France, Germany, and the Netherlands, NASEM notes. They recommend aligning the U.S. with these countries.

5. Require a Minimum Disinfectant Residual Throughout Public Water Systems and Concomitant Monitoring for Legionella

AWWA Water Science research published in 2019 found data that suggest a relationship between Legionella pneumophila growth and public water systems where free chlorine residuals were less than 0.1 milligrams per liter. The researchers recommend maintaining chlorine residuals of at least 0.1 milligrams per liter in all parts of water systems to prevent outbreaks. However, they note that Legionella pneumophila may still occur in low concentrations when free chlorine residuals are more than 1.0 milligrams per liter, even in well-maintained systems.

NASEM is urging the EPA to require a minimum disinfectant residual throughout public water systems and to validate treatment performance with routine monitoring for Legionella pneumophila from sampling sites that are representative of the distribution system.

While the EPA is considering including Legionella pneumophila in the next version of its Unregulated Contaminant Monitoring Rule for drinking water in 2022, the NASEM committee says water utilities can start taking preventive actions now. They can begin by collecting information and setting internal targets for optimizing their internal distribution systems.

NASEM's committee acknowledged that its five recommendations entail training and education for a wide range of professionals, such as building owners and operators, engineering consultants, clinicians and epidemiologists, inspectors, and lab technicians. Implementing the suggestions could take five to 10 years, the group said. Although that might sound like plenty of time, professionals in public health department labs, distribution water systems, and communities across the country can start working now to reduce the risk of this preventable disease by adopting the committee's suggestions.