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Legionella  bacteria are one of the top three causes of non-epidemic, community-acquired pneumonia, and are cited as the indoor building contaminant bacteria most likely to result in mortality. Legionella bacteria are found naturally in the environment, usually in warm water. People breathe mists or water vapor that is contaminated with the bacteria allowing it to grow and thrive in the lungs.  According to the U.S. Centers for Disease Control and Prevention (CDC), sometimes the bacteria infect the lungs and cause pneumonia — if so, it is called Legionnaires' disease.

The first recognized outbreak of Legionnaires’ disease occurred in July 1976 following an American Legion convention in Philadelphia. Attendees started to become sick, and several passed away. According to the New York Times, 221 individuals eventually became ill and 34 died.  By January 1977, CDC identified Legionella bacteria as the cause and found it in the cooling tower of the Bellevue-Stratford Hotel, where the convention took place.

Legionnaires’ disease has been linked to exposure to contaminated water supplies in residences, commercial office buildings, schools, rehabilitation centers, nursing homes and industrial water supplies.  Look at these recent cases:

  1. In August 2015, an outbreak in Legionnaire’s disease sickened at least 127 people and killed 12.  The source of the bacteria was a hotel’s cooling tower. 
  2. In late October 2015, In Wenatchee, Washington, an investigation is underway at a grocery story suspecting that misters used in the produce department could be the source of Legionnaire’s disease that sickened four in the area.  
  3. According to news reports, also in late October, school officials at Berlin High School in Berlin, Connecticut notified parents because Legionella, the bacteria that caused Legionnaire’s Disease was found in the school’s water supply.  No one became ill but the school had to hire a contractor to disinfect the school. 
  4. The state of Illinois is spending $2.3 million to fix a water system linked to a Legionnaire’s disease outbreak that is believed to have killed 12 residents at a veteran’s home.

Where Legionella lives

Many agree -- regular service and maintenance can help eliminated the problem, the buildup on Legionella bacteria. And, it’s not just cooling towers that need to be maintained.  Improper operation and maintenance of many water disseminating devices or systems increases their potential to harbor, amplify and transmit Legionella  including:

—  Domestic hot water distribution systems – the primary source of infections that develop in healthcare settings and a significant source for other sporadic cases—  Cooling towers and evaporative condensers (swamp coolers)—  Spas and whirlpools (on display or otherwise in use)—  Humidifiers—  Supermarket reservoir misters—  Respiratory therapy equipment—  Water fountains—  Hot springs (artificial waterfalls)—  Dental hygiene equipment—  Cold water systems (ice machines, storage tanks)—  Fire suppression systems

Legionella may also be spread through an HVAC system that is not properly treated and well-maintained. For this to occur, water contaminated with the bacteria must enter the system, through a humidifier, poorly placed air intake unit, or other pathway.

Risk Management Strategies

According to XL Catlin’s Environmental Risk Engineering team, the risk of Legionnaire’s disease may be reduced by implementing a written Water Management Program, which should include operational controls that address the temperature to be maintained for circulating water systems; disinfection for cooling towers and HVAC pipes; water system disinfection methods and frequency; and maintenance for water filters and water tanks. Additional controls for whirlpool spas and similar features may include water replacement intervals, and special controls for disinfection and filtration.  Detection of Legionella should trigger a review of risk management procedures. Written procedures for decontamination of devices should be available to deal with an outbreak of illness or for other conditions that have been specified as constituting a substantial risk.

Creation of a water safety program is an effective tool for increasing building owner and property manager awareness of Legionella risks and appropriate controls. The elements of the plan can be used to create a training program for staff responsible for building water systems and maintenance. Effective implementation of a water safety plan and periodic review of controls will establish a standard of care and should help reduce potential liabilities and claims costs.

For more guidance on how to reduce legionella risks, download XL Catlin’s Environmental Risk Bulletin: Legionella and Risk Management.


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Global Asset Protection Services, LLC, and its affiliates (“AXA XL Risk Consulting”) provides risk assessment reports and other loss prevention services, as requested. This document shall not be construed as indicating the existence or availability under any policy of coverage for any particular type of loss or damage. AXA XL Risk. We specifically disclaim any warranty or representation that compliance with any advice or recommendation in any publication will make a facility or operation safe or healthful, or put it in compliance with any standard, code, law, rule or regulation. Save where expressly agreed in writing, AXA XL Risk Consulting and its related and affiliated companies disclaim all liability for loss or damage suffered by any party arising out of or in connection with this publication, including indirect or consequential loss or damage, howsoever arising. Any party who chooses to rely in any way on the contents of this document does so at their own risk.

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