Mitigating Risk: How to Avoid Legionnaires’ Disease Becoming Act 2 in the Global Pandemic.

Closing buildings for months during COVID-19 has created the perfect environment for Legionella to breed in building water supplies. What can be done to prevent an outbreak?

June 17, 2021

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As discussed in part 1 in this series, Legionnaires’ disease poses a very serious health threat, with a mortality rate that far exceeds that for COVID-19 and a perfect storm of unexpected conditions in thousands of buildings across the world has left us extremely vulnerable to an outbreak thanks to the prolonged absence of people.


Legionella bacteria, the causative agent of Legionnaires’ disease live in water. The very water you have been told to wash your hands in, has sat and stagnated for months. Even the municipal water supply can become a source of contamination if not enough water is moving through the supply lines. Free chlorine effectively dissipates as the water sits, removing any barrier to bacteria that would otherwise have been held at bay.


What steps can we take to address Legionella risks?


Public health agencies, including the CDC, have warned of the risks posed by Legionella, but little actual guidance on what to do has been provided. The Safe Drinking Water Act does not necessarily mean water is safe or palatable. Water problems existed in many areas before 2019, and there is no requirement for municipal water suppliers to test for, or ensure drinking water is free from the Legionella bacteria.


Figure 1. The water supplied on this building supply line met all of the requirements under the Safe Water Act.1


Flushing, pasteurization, hyperchlorination, and water testing have all been proposed as strategies to deal with the threat of Legionella, but the truth is that some of these methods work better than others, and none will work as a stand-alone solution to the problem. So, what can be done to address the problem?


Stepwise re-opening to mitigate the Legionella threat


In an ideal world, local government and municipal water suppliers will work with building owners to implement a stepwise re-opening plan. The first step of which is for municipal water suppliers to flush out their own supply lines, replacing stagnant un-chlorinated water with a fresh chlorinated supply. Only then can building owners undertake a multipoint building sterilization plan to safely bring their building back online.


  • Depending on the building, some upfront testing may be advisable. This has the potential to reduce and focus efforts, and act as a driver for the next steps.
  • Hyperchlorination, followed by flushing, followed by a rest period of 5-7 days to let the system return to normal before any testing to make sure we capture any rebound in bacterial numbers.
  • Testing or re-testing, to determine if the water is now safe, with additional targeted hyperchlorination as required, until all samples come back negative.



Other factors to consider

  • Culture testing takes time, typically 3-7 days to get results, but it is the only way to be sure about a water sample. PCR and other methods will often return false-positive results as they only detect the presence of Legionella DNA which provides no information on the viability or infective ability of any bacteria present.
  • Never let anyone collect a sample from your building without also collecting a parallel sample for yourself. Health authorities, the CDC, etc., may not share data with you and in the event of questioning, these samples will be invaluable.
  • Call your insurer and find out what you are covered for in the event of an outbreak, and what part of the proactive measures they might cover.


Finally, remember that Legionella does not discriminate between buildings new or old. If the bacteria have gained access or multiplied during the COVID-19 shut down, then there is potential for infection and an outbreak could easily result in a building being shut down again for many months while expensive remediation steps are implemented.


Access Dr David Krause’s webinar to learn more about managing Legionella risks in building water systems, and waterborne pathogen outbreak best practices: prevention, investigation and remediation. Then tune in for the final blog in this series , where we willdiscuss how to improve testing and ensure you are giving yourself the best possible chance of detecting Legionella.


Learn more about membrane filtration for simple efficient water testing for Legionella


In the event of Immediate Critical Contamination and Outbreak, please call Pall’s Emergency 24hr Outbreak Hotline: 1-866-347-3428. Pall can rapidly deploy Point-of-Use Water Filters to deliver an immediate barrier against Legionella outbreak. 


Image credit Dr David Krause, taken from the webinar Reopening Hotels, Office Buildings And Healthcare Facilities After The COVID-19 Pandemic: Managing Legionella Risks In Building Water Systems

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