Managing Legionella Risk in the Age of COVID-19

Oct. 1, 2020

This article originally appeared in WQP October Commercial Water 2020 issue as "Party in the Pipes" 

About the author:

Janet E. Stout, PhD, is president for Special Pathogens Laboratory. Stout can be reached at [email protected].


It is hard not to think about anything besides COVID-19 these days, but this virus is not the only pathogen we need to worry about. In fact, COVID-19 is causing us to worry even more about the bacteria Legionella and the life-threatening pneumonia it causes—Legionnaires’ disease. 

Certainly, cases of COVID-19 infections are occurring rapidly with more than 4 million in the U.S. alone, but tallying up the 50,000-plus annual reported cases of Legionnaires’ disease since its discovery in 1976 finds 2 million cases. Although COVID-19 and Legionella have different modes of transmission, the mortality rates for Legionella contamination are much higher at 10% to 25% depending on if acquired in a community or hospital. Interestingly, one patient was recently reported to have been infected with both COVID-19 and Legionella.

Comparing COVID-19 & Legionella

Why does COVID-19 cause us to worry more about Legionella? The COVID-19 shut down has affected the quality of water in our building water systems where Legionella grows and spreads. Stay at home advisories and operating restrictions have decreased water use and demand in large buildings and hospitals. 

COVID-19 and Legionella both cause serious lung infections and the people affected are often both the elderly and infirmed. These individuals are the occupants of nursing homes, senior retirement communities, healthcare facilities, hotels and entertainment venues, such as casinos. All of these facilities have been operating at low or no occupancy and under low or no flow conditions. This low-use situation caused stagnation and increased the time water is in the pipes (water age). When this happens, water quality is degraded and bacteria thrive.

Taking advantage of this situation, bacteria like Legionella have what we call a “party in the pipes.” Legionella bacteria grow especially well when the water is near body temperature, when it is in close association with other microbes and where there are nutrients. These conditions are met in dormant buildings or unoccupied hospitals and commercial spaces. Other waterborne bacteria, such as Pseudomonas aeruginosa and mycobacteria may also be at the party and can cause serious infections.

Now, more than ever, the water systems of these affected buildings need to be evaluated for Legionella and waterborne pathogen risk. History shows that we should be concerned about the opening of buildings or healthcare facilities after being dormant. The current situation is reminiscent of construction-related outbreaks of Legionnaires’ disease. Water remained in the pipes, Legionella proliferated and then the building resumed normal operation, leading to increased cases of Legionnaires’ disease followed along with deaths. We must learn from the past or we are destined to repeat it as the saying goes.

Managing Legionella Risks

How do we meet this new challenge safely and effectively? Special Pathogens Laboratory has developed an easy to follow guide that can be accessed at

This guidance includes:

  • How to prevent Legionella from spoiling reopening; 
  • Reopening checklist; 
  • Reopening Legionella testing; and
  • Remediation resources for building water systems.

The water treatment professional is also a key resource for responding to this threat. They are the frontline protectors of water quality and water safety. Building managers and water treatment professionals need a short-term and long-term plan for Legionella water management. The above mentioned “remediation resources for building water systems” lists water treatment professionals by region that can help disinfecting building water systems if needed.

The most common short-term remedy will be a shock disinfection with an oxidizing biocide. Develop a disinfectant sampling, monitoring methods and documentation plan for the disinfection procedure and execution. Do not underestimate the time and effort required to complete this process successfully.

Testing for Legionella within 48 hours of completing a shock disinfection demonstrates the effectiveness of the procedure in reducing Legionella within the system and mitigating the risk of exposure. Note that any shock treatment will temporarily reduce Legionella and levels will return to baseline without ongoing mitigation efforts.

Whether a building needs to be disinfected for Legionella control depends on whether it is colonized with Legionella. This can only be determined by testing the water for Legionella. The gold standard method for testing is the standard culture method. This needs to be done approximately two weeks prior to occupancy to allow for the test results to be known and a response planned.

Buildings need a water safety and management plan as described in the ASHRAE Standard 188. Buildings without a plan will need one to minimize water-related risks at their facility and to demonstrate due diligence. The purpose of a water safety and management plan is to minimize Legionella and other waterborne pathogens risks associated with building water systems. A robust plan will have recommendations and actions to be followed during low or no flow situations. 

In addition to having a water safety and management plan, long-term strategies include periodic testing and monitoring of cooling towers, decorative water features and the warm water distribution system.

You might be wondering who is qualified to help with Legionella water management and proactive prevention. Up until recently, it was buyer beware or catch as catch can when selecting your Legionella water safety consultant. A new professional qualifications standard has been published that takes the guesswork out of this decision. ASSE/IAPMO/ANSI 12080 outlines the minimum knowledge and competency needed to perform a Legionella risk assessment. Learn about the new ASSE Standard 12080 and the IAPMO training for the certification examination at

You are now well equipped to meet this COVID-related challenge. Legionella is betting that you will not crash the party in the pipes. Prove Legionella wrong. 

Sponsored Recommendations

SmartSights WIN-911 Alarm Notification Software Enables Faster Response

March 15, 2024
Alarm notification software enables faster response for customers, keeping production on track

Automated Fresh Water Treatment

March 15, 2024
SCADA, Automation and Control for Efficient and Compliant Operations

Digital Transformation Enables Smart Water

March 15, 2024
During this webinar we will discuss factors driving the transformation to digital water, water industry trends, followed by a summary of solutions (products & services) available...

Smart Water Solutions: Transforming the Water Universe

March 15, 2024
Water is our most valuable resource, and efficient and effective water and wastewater handling is crucial for municipalities. As industry experts, you face a number of challenges...