Legionella Management Basics

Legionella bacteria presents serious health risks that can be mitigated with proper professional guidance—this article offers background and steps toward Legionella management.

Robust Legionella management is an important element of safe water system operation for a range of structures and facilities. Legionella is the bacteria that causes Legionnaires’ disease—a severe, potentially fatal form of pneumonia. The bacteria can grow in building cooling and plumbing systems, and it presents significant health, legal, and financial risks if it is not managed properly. Management of Legionella should include a combination of routine monitoring for growth of the bacteria, regular water system maintenance, and proactive water system treatment as necessary.

Fast Facts and Legionella Management Basics:

The numbers shown here are the rate of cases/100,000 population.
Source: National Notifiable Diseases Surveillance System

About Legionnaires’ disease
Most cases of Legionnaires’ disease are caused by a single species of Legionella bacteria known as Legionella pneumophila. The disease was initially identified following an outbreak of pneumonia among attendees of an American Legion convention in Philadelphia, PA, in 1976. Since this outbreak, the reported number of cases of Legionnaires’ disease observed annually has continued to rise as healthcare providers institute increase surveillance for the disease. The Centers for Disease Control and Prevention (CDC) indicates that Health departments reported nearly 10,000 cases of Legionnaires’ disease in the United States in 2018.1 However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate the true incidence.1 Legionnaires’ disease proves fatal for about one out of 10 people who contract the disease.

How Legionnaires’ disease is contracted
Infection may occur by inhalation of Legionella bacteria contained within airborne water droplets. These water droplets may be formed from aerosolizing water systems, such as cooling towers and decorative fountains. The bacteria may also be introduced to the respiratory system through a process known as aspiration. Aspiration occurs when small droplets of water enter the trachea instead of the esophagus. This can occur when an individual chokes while drinking water (when water “goes down the wrong pipe”). In 2016, one potential case of human-to-human Legionnaires’ disease transmission was reported in Portugal.2 However, decades of prior research has failed to identify person-to-person transmission of the disease among susceptible populations, suggesting that this mode of transmission is extremely rare.

Those at risk of contracting Legionnaires’ disease
Typically, healthy individuals who are exposed to Legionella bacteria are not at a high risk for infection. According to the CDC, the following risk factors3 make an individual more likely to contract Legionnaires’ disease following exposure to Legionella bacteria:

  • Age (>50 years)
  • Smoking
  • Chronic lung disease
  • Cancer
  • Weakened immune system/consumption of immunosuppressing drugs
  • Other underlying illnesses (diabetes, kidney failure, liver failure, etc.)

Environments that require Legionella management
Legionella management is a key concern in the operation and maintenance of large, complex water systems and water systems that generate aerosols, especially those serving populations with a high incidence of the risk factors described above. Occurrences of Legionnaire’s disease are most often associated with Legionella that grows in the cooling towers or plumbing systems of large facilities like hospitals, long-term care facilities, hotels, and cruise ships—but the bacteria can also be found in decorative fountains, hot tubs, and domestic hot water systems. The bacteria typically grows in hot water systems that maintain water temperatures between 70 – 120°F, but growth in cold water systems can also occur if temperatures reach this range.

Legionella management guidance
The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) has developed industry standard ASHRAE 188-2015, which provides minimum Legionella risk management requirements for building water systems. These requirements include development of a water management program for buildings that possess factors that place them at a higher risk for Legionella growth and transmission. The CDC has issued additional guidance for development of water management programs that comply with the requirements developed under ASHRAE 188-2015. Additional technical guidelines that include recommendations for Legionella management have been developed by the Occupational Safety and Health Administration (OSHA) and the Cooling Technology Institute (CTI).

What is a water management program?
A water management program is a comprehensive plan that applies risk management principles to the control of Legionella growth in building water systems. Water management programs vary based on the type of facility, but they typically include the following elements:

  • Identification of program team
  • Description of facility water systems (narrative and flow diagrams)
  • Building water system risk analysis
  • Legionella control measures
  • Monitoring/corrective actions
  • Procedures for evaluating the water management program’s effectiveness
  • Documentation and record-keeping procedures

Contact Scott Quinlan, PE, 412.399.5385, for more information about GAI’s Legionella management and water management program support services.

Scott QuinlanScott Quinlan, PE specializes in water and wastewater engineering, water resource planning, alternative water supply, and project funding. He has strong project management skills in addition to his process engineering capabilities. Scott is responsible for client management, utility valuation, and development of municipal capital improvement programs for both water and wastewater systems.


1 Case Definitions; Centers for Disease Control and Prevention

2 Probable Person-to-Person Transmission of Legionnaires’ Disease; New England Journal of Medicine

3 Causes, How it Spreads, and People at Increased Risk; Centers for Disease Control and Prevention

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