How to Prevent Legionella Outbreaks in Your Facilities

Five steps to incorporate water management planning into your overall building safety plans

Prevent Legionella Outbreaks

The risk of Legionella bacteria in manmade water systems has never been greater, with tens of thousands of buildings closed or experiencing very little water flow since the COVID-19 pandemic forced sudden and extreme quarantine measures. Recent reports of Legionella detection in closed schools and other facilities underscore the need for facility maintenance professionals to proactively address the risks associated with low water demand, such as waterborne illnesses.

Legionnaires’ disease—deadly in 10% of community-acquired cases—was already a rapidly increasing burden in the United States prior to the COVID-19 pandemic. Since 2000, the U.S. Centers for Disease Control and Prevention (CDC) reported an eight-fold increase in Legionella cases, making this bacteria the No. 1 cause of waterborne disease outbreaks in the U.S.

A 2019 National Academies of Sciences, Engineering, and Medicine report on managing Legionella risks in building water systems estimated there are 52,000 to 70,000 Legionella cases in the U.S. annually. This estimate is about 10 times higher than the number of cases officially reported to the CDC.

Still waters breed bacteria

Buildings impacted by low occupancy during the COVID-19 pandemic face water quality degradation due to the unprecedented decline in water demand. Specifically, increased water residence time in domestic water systems may cause:

  • Amplification of Legionella, which can become aerosolized and lead to Legionnaires’ disease, or Pontiac fever
  • Growth of additional microorganisms that causes gastrointestinal or other respiratory infections
  • Decreased temperature in hot water systems
  • Elevated temperature in cold water systems
  • Increased sediment and corrosion
  • Disinfection level reduction due to increased residence times
  • Leaching of lead or copper due to increased corrosion, including fixtures classified as

The changes in building occupancy and usage caused by the pandemic have created new challenges for water safety. In addition to public health concerns, the financial costs of Legionella are high.

According to a 2012 study, “Direct Healthcare Costs of Selected Diseases Primarily or Partially Transmitted by Water,” insurance companies estimate an annual total cost of US$434 million for claims arising from Legionnaires’ disease with a total health care cost of $38,363 per patient. The total annual economic cost of waterborne pathogens including Legionella pneumophila, Mycobacterium avium, Pseudomonas aeruginosa, and Acanthamoeba is $1 billion, according to a 2015 paper published in Pathogens, “Opportunistic Premise Plumbing Pathogens: Increasingly Important Pathogens in Drinking Water.”

Monitor water pathogen risk factors

Plumbing, pools and spas, cooling towers, on-site water storage, decorative fountains, and ice machines are examples of building water systems associated with elevated water pathogen risk.

Specific factors that cause Legionella to grow in these systems include:

  • Tepid water temperature: Hot water systems, spas/swimming pools, and showers are responsible for the majority of outbreaks. Warm water, between 77 F and 108 F, is the optimal temperature range for Legionella growth.
  • Lack of disinfection/infrequent use of fixtures: Not all areas receive equal amounts of use, disinfection treatment, and/or cleaning; occupancy fluctuation can allow fixtures like shower heads, faucets, etc., to grow biofilm, causing the bacteria to thrive.
  • Complex plumbing designs: Dead legs (a length of pipe leading to an outlet that is rarely or never used) and other design complexities can cause water to stagnate and create low/poor flow.

Steps for long-term safety

Outbreak prevention is possible with effective water management. A 2016 CDC study showed that nine of 10 Legionella outbreaks were preventable.

Facility managers need to incorporate water safety into business continuity plans following this unprecedented downturn in demand. Facility reopening strategies must include a coordinated evaluation of a building water system and the development of a management plan to ensure water systems can be used safely.

Here are five practical steps to take now, along with strategies for creating site-specific water management plans that incorporate water management planning into the long-term safety and resiliency of your buildings.

1. Keep water flowing to reduce water age and chlorine depletion. Conduct an environmental assessment using a site-specific flow diagram to identify and record areas of low use and show the flow of hot and cold water throughout plumbing configurations and appliances. The flow diagram should include all components of water systems, including showerheads, backflow preventers, irrigation equipment, fire suppression equipment, cooling towers, ice machines, pools and spas, and dead legs. Effective flushing programs require an initial flush to remove low quality water and contaminants, followed by subsequent flushes to provide water with acceptable levels of disinfectant residual.

2. Frequently and strategically monitor disinfectant residuals. Monitor temperature and disinfectant residual levels at the identified stagnation points/dead legs in the building’s water system. Develop a monitoring method and schedule for temperature and disinfectant residuals for both hot and cold water systems, including sampling points of entry and points of use farthest from the main. Monitor chlorine residuals at strategic locations to ensure water of acceptable quality is reaching all points of the building water system. Building water systems require oversight when chemicals are added that could pose a risk to public health or cause an exceedance of maximum contaminant levels (MCL). Hospital or building plumbing codes and procedures must be incorporated into water management plans when implementing monitoring and control processes. Measure supplemental disinfectant residuals twice weekly to meet safe drinking water standards.

3. Maintain routine treatment of cooling towers and other aerosol-generating water systems. Cooling tower water systems can transmit contaminated aerosols into a building or about 2 km away from the tower. Reopening procedures for evaporative cooling systems should include offline cleaning and disinfection, inspections, preventative maintenance, and testing for Legionella. Following start-up, routine chemical treatment, maintenance, cleaning and disinfection, and testing should be maintained to mitigate hazards. Most health departments have no way to identify how many cooling towers are in their jurisdiction. Cooling tower registries and water management plans assist with managing risks from cooling towers. Other aerosol-generating systems such as decorative fountains, spas, HVAC humidifiers, and irrigation should be flushed with the rest of the building water systems, cleaned, and disinfected prior to reopening. When water sources are disabled, it is important to not only drain the system completely and disinfect all parts, but also to monitor each supply line to the deactivated system. The line becomes a point where standing water can occur and it should be drained weekly.

4. Follow normal water quality monitoring, inspection, analysis, and cleaning strategies. Allow for normal procedures, paying special attention to drinking fountains, showers, swimming pools, tanks, water treatment equipment, and emergency systems/equipment. Where applicable, there must be a temperature and disinfectant residual profile of the water system that informs the monitoring and sampling strategy, including critical points such as boilers, heat exchangers, storage vessels, water hammer arrestors, dead ends, recirculating loops, risers, and end points that reflect the flow of hot water throughout the system. High-risk points, such as dead ends and locations with lower utilization, should be captured in the profile.

5. Maintain defensible records showing verification and validation of safety steps. Good records provide a reasonable level of assurance that maintenance workers are managing risk. Facility managers should document all results from reopening procedures and incorporate them into the overall water management plan. They also should reevaluate plans to ensure necessary control measures are carried out consistently and expectations are being met.


Water Management Resources

There is no shortage of guidance and regulatory expectations available to help building owners and facility managers care for water systems in buildings of all sizes. Among them:

Posted On October 8, 2020

Chris Boyd

Chris Boyd is general manager of Building Water Health at NSF Health Sciences, LLC, a company of NSF International, a global public health organization based in Ann Arbor, Michigan. Boyd and the Building Water Health team organize the annual Legionella Conference. A former public health official in New York City, Boyd led the city’s response to the 2015 Legionnaires’ outbreak, the largest in its history, and oversaw implementation of the first Legionella-controlling regulatory standards for cooling towers. He can be reached at [email protected].

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