I know one thing, the moment you say “Legionella” to a group of plumbing engineers, everyone pays attention.

It’s the likeliest word in our verbal repertoire to set off alarm bells next to the word “lead.” Ironically, “plumbum” is the base word for plumbing and also the Latin word for lead, which is now known to be a poisonous material plumbing engineers attempt to avoid at all costs. Maybe we should rename our profession to “legionell-ing” engineers, since our shift to learn as much as we can on how to avoid these bacteria at all costs. But I digress…

Here are four facts about Legionella and why we as plumbing engineers should care.

Fact No. 1: Legionella is a general category of bacterium that is commonly found in our water supplies

There are over 60 different species of bacterium, of which 25 are known to be implicated in human disease. There is one king of the species, Legionella pneumophila, which is responsible for approximately 90% of all infections. The remaining non-pneumophila species (found in water and soil) are considered non-pathogenic until shown to cause disease. Of the reported cases to the Centers for Disease Control and Prevention (CDC), less than 5% are attributed to non-pathogenic species.

As previously mentioned, Legionella pneumophila is responsible for most infections. Anyone who gets sick after being exposed to Legionella bacteria will likely be diagnosed with either Legionnaire’s disease or Pontiac Fever. Typical symptoms are cough, shortness of breath, fever, muscle aches and headaches. Nausea, diarrhea, vomiting and confusion can also be symptoms. However, Legionnaires’ disease is often misdiagnosed as other types of pneumonia because it will look the same on an X-Ray. The only way to know if you have Legionnaires’ disease is through specific testing. The good news is, this testing is becoming more commonplace. The bad news, we are seeing cases of Legionnaires’ disease rise significantly.

Fact No. 2: These infections are presenting with startling severity 

About 1 out of every 10 people diagnosed with Legionnaires’ disease will die due to complications from their illness. For those who get Legionnaires’ disease during a stay in a health care facility, the mortality rate climbs to about 1 out of every 4.

Plumbing engineers have good reason to be so concerned about Legionella as plumbing domestic water systems are the predominant source of the bacteria. Legionella bacteria are found in freshwater distributed by municipalities to buildings and homes. The bacteria do not represent a significant health concern until they grow and spread in a facility’s water piping networks. If Legionella grows in a plumbing system, the bacteria can spread to humans via small droplets and/or vapor inhaled into the lungs. Common sources where these droplets are “made” include:

• Showerheads and sink faucets;
• Cooling towers;
• Hot tubs;
• Decorative fountains and water features;
• Hot water tanks and heaters; and
• Large, complex plumbing systems.

So how do the bacteria grow and spread? There are several factors, all of which should be concerning to plumbing engineers. Water temperature, disinfectant residual, stagnation and quality as well as pipe materials and other factors can all contribute to the development of Legionella pneumophila growth in the domestic water system. The larger and more complex the building is, the more challenging it is to maintain a healthy, balanced system. Complicating this further, the age, location, surrounding environment and incoming water quality can also have a significant impact on the development of Legionella bacteria.

Legionella bacteria have an ideal temperature range for growth which also happens to be right in the sweet spot most building occupants favor for washing, bathing, showering or soaking in a hot tub. And if the building occupants are in a higher risk category, you may have to consider more options, such as supplemental disinfection to keep occupants safe.

Fact No. 3: Plumbing engineers are being asked to play the role of chemist and microbiologist as we design systems to protect the public

We are increasingly responsible for analyzing and understanding the water chemistry behind the development of Legionella — and then how to successfully control it. I’m not sure this falls under what we consider our “standard of care” when it comes to engineering services, but this is the world we live in. Gone are the days when our biggest concern was making sure hot and cold water came out of the correct side of the faucet.

Fact No. 4: There is no simple answer to any of this, but working together, we can make a difference

As plumbing engineers, it is imperative we constantly try to learn as much as possible about this threat and about the options available to reduce the risk. I emphasize that the goal is to reduce the risk. We cannot, and should not, ever guarantee complete elimination of waterborne pathogens in a plumbing system. Our responsibility as engineers is to design a system that is capable of reducing the risk. It is the responsibility of the building operators to run the building within the design parameters for any of this to be successful.