What is Legionella and Why Should You Care?

By Chad Edmondson


Legionella. It is a potentially fatal bacterium that for the most part has managed to fly under the radar of the general public since it was first determined as the cause of Legionnaires’ disease in the 1970s.  Despite the fact that there are well-known techniques to prevent the growth of the causative bacteria, legionellosis (commonly known as Legionnaires’ disease) has taken the lives of well over 100,000 people in the U.S. alone.  Furthermore, reported cases of the bacteria has risen 217 percent in just the last decade, according to the Centers for Disease Control and Prevention. 

What is Legionella?

There are over 50 known species of Legionella, a common aquatic bacterium.  The most worrisome of these is Legionella pneumonia, the species associated with the vast majority of legionellosis cases.  Legionellosis or Legionnaire’s disease is an acute bacterial infection of the lower respiratory tract and is accompanied by pneumonia. 

Legionella can be found in both natural and man-made water systems, including hot tubs, cooling towers, hot water tanks, and plumbing systems.  The bacterium was originally identified in 1976 when a large number of people attending a Legionnaires’ convention in Philadelphia became ill (hence the naming of the disease), but documented cases of the disease date back to 1947. 

The symptoms of Legionnaires’ disease are similar to pneumonia.  It is contracted through inhalation (not person-to-person contact), which makes aerosolized water a frequent culprit.  There is no vaccine, but antibiotics can be used to treat the infection.

What HVAC and Plumbing Professionals Should Know

If Legionella prevention isn’t on the radar of HVAC and plumbing professionals, it should be – especially now. 

An article in last month’s Plumbing Engineer magazine clarifies the relevance of understanding Legionella when it comes to designing energy efficient plumbing systems.   In the article, Scott Baron, a Plumbing Engineer and a registered Professional Engineer in Chicago, identifies a potential conflict between ASHRAE 90.1 energy efficiency requirements and the best prevention practices against Legionella. 

ASHRAE 90.1 mandates that domestic hot water systems have adjustable temperature controls that can be turned down to 120°F or lower.  While this is a useful energy savings measure, Baron explains that this practice could also lead to more favorable conditions for Legionella to survive.  Specifically, if hot water pump recirculation is timed out for any length of time in a turndown design, it could lead to water stagnation in part of the piping, increasing the risk of Legionella growth, and thus its associated risks. Legionella can survive in up to 122°F water – and even above that in certain conditions that allow for its protection. 

ASHRAE Standard 188

Perhaps in response to some of these concerns, ASHRAE has initiated a new standard of practice for facility managers/owners to prevent Legionellosis associated with building water systems.  Standard 188 aims to reduce the risk of legionellosis thru specific measures that identify and subsequently address the risk of Legionella.  The standard is modeled on the principles of Hazard Analysis and Critical Control Point (HACCP) plans, which have been widely used to prevent disease from infectious organisms transmitted from food and water. 

While the Standard 188 will require facility managers/owners to formally take responsibility for controlling Legionella in their building water systems, it is likely to take a while longer for it to go into effect.  Even though development of the standard began in 2006, a 4th draft is still currently in review.  With any luck, it may be officially published in 2015. 

Stay tuned for more on ASHRAE Standard 188 and preventive measures for Legionella in hot water systems in upcoming blogs.