How to Prevent A Legionella Outbreak

graphic showing outdoor cooling tower system and says 'how to prevent legionella outbreaks'

Water safety and quality have been some of the United States’ most pressing concerns in recent years with cities like Flint, Michigan and the Bronx in New York reporting disease as the result of poor water quality. Ensuring the safety and health of your staff and clients is one of the most important things on your mind. Providing safe, disease-free water, however, requires learning more about water-borne, disease-causing bacteria and how to combat them. Of particular concern is the detection of Legionella pneumophila.

What Is Legionella?

Legionella refers to a family of over 50 species of disease-causing aquatic bacteria. Found primarily in freshwater environments across the world, like lakes, streams and man-made water systems, Legionella is largely harmless in natural environments. However, with the use of dark, warm, stagnant human water systems, Legionella has arisen as a prominent disease-causing agent. In these environments, Legionella thrives. Legionella bacteria tend to grow in temperatures ranging from 68 to 122 degrees Fahrenheit, with optimal growth occurring between 95 and 115 degrees, and typically prefer a pH between 5.0 and 8.5, typical conditions for many water systems across the United States.

legionella bacteria grows in temperatures ranging from 68-122 degrees Fahrenheit statistic graphic

The most deadly species of the Legionella family is Legionella pneumophila, a species name meaning “lung-loving.” This particular variety was the first Legionella species described, discovered following an outbreak at an American Legion convention in Philadelphia in 1976. Later, the species was split into 15 serogroups based on the cell surface antigens of each organism. Only a few of these serogroups are pathogenic. However, the most prevalent serogroup, serogroup 1, is pathogenic in nature. As a whole, L. pneumophila is closely associated with human disease, causing about 70 percent of Legionella infections in Europe. 

What Is the Impact of Legionella?

Legionella poses a serious health risk to people around the world. Any infection of Legionella bacteria is called “legionellosis,” but this infection can result in one of three distinct diseases, distinguishable by their different symptoms. These diseases are:

  • Pontiac Fever: Named after the town in Michigan in which the disease was discovered in 1968, Pontiac fever affects 95 percent of those exposed to the Legionella bacteria. A milder form of Legionnaires’ disease, Pontiac fever symptoms include fever and muscle aches starting anywhere from hours to days after exposure to the Legionella bacteria. Typically the symptoms last less than a week, and a patient can usually recover from the disease without specific treatment.
  • Legionnaires’ Disease: Discovered in 1976 after an outbreak at the Philadelphia convention of the American Legion, Legionnaires’ disease affects up to five percent of all people exposed to the Legionella bacteria. The disease itself is a more severe form of Pontiac fever, involving additional symptoms of pneumonia. In addition to muscle aches and fever, symptoms of Legionnaires’ disease include cough, shortness of breath and headaches. Less common symptoms include diarrhea, nausea and confusion. These symptoms typically begin two to 10 days after exposure to the Legionella bacteria and can last for a few weeks. According to the CDC, about 6,000 reported cases of Legionnaires’ disease occurred in 2015, and an average of 5,000 cases occur annually. However, since Legionnaire’s Disease is underdiagnosed, the number of infections occurring annually is likely much larger.
  • Extrapulmonary Variants: In rare cases, Legionella can spread from the respiratory system to the rest of the body, infecting the spleen, liver, kidney, bone, digestive tract, and, most commonly, the heart. Symptoms include fever, night sweats and organ failure. These infections are most common in hospitals where patients with open wounds and suppressed immune systems are more common and more vulnerable.

legionnaires' disease affects up to 5% of all people exposed to Legionella bacteria

These diseases can be differentiated and diagnosed with a simple blood or urine test. Legionnaires’ disease sufferers may undergo an additional chest x-ray or sputum test to confirm the diagnosis. Sufferers of extrapulmonary infections may need additional tests to confirm the cause of the infection. Immediately after diagnosis, doctors will usually ask the patient questions to determine the possible source of the infection so they can report the outbreak to the proper authorities.

While most healthy people can successfully fight off a Legionella infection after exposure, people belonging to some key demographics tend to be at higher risk for infection and complications. People with the following attributes tend to be more susceptible to a Legionella infection:

  • Advanced Age: People over the age of 50 tend to have weaker immune and respiratory systems than younger individuals, and therefore are at a higher risk of contracting Legionnaires’ disease.
  • Smoking Habit: Both current and former smokers tend to have weaker respiratory systems and are therefore less able to fight off respiratory infections than non-smokers.
  • Chronic Lung Disease: Since Legionella tends to affect the human respiratory system, sufferers of chronic lung diseases, such as chronic obstructive pulmonary disease, emphysema and asthma tend to be more likely to feel the full effects of the bacteria.
  • Weakened Immune System: Cancer patients, diabetics and people suffering from kidney failure tend to have weakened immune systems and are therefore more likely to experience a Legionella infection. This is also true of people taking drugs specifically to suppress the immune system, such as transplant patients and chemotherapy recipients.

Though there is no vaccine for these diseases due to their bacterial nature, they are treatable. If you get Legionnaires’ disease or an extrapulmonary infection, you’ll likely need hospital care and a round or two of antibiotics to get rid of the disease. While this helps reduce the lethality of the infection, complications still occur — among Legionnaires’ sufferers, lung failure is a possibility for people already suffering lung problems, and around one in 10 infected individuals still die from the disease due to complications. 

What Causes Legionella Outbreaks?

Legionella bacteria spread by aspiration – breathing in the bacteria. Since the bacteria are aquatic, this means a potential victim of the disease has to inhale water droplets containing Legionella bacteria in order to facilitate the infection. This can happen in one of two ways:

  • Breathing Moist Air: Steam coming off a hot tub, fountain or other water source consists of water droplets large enough for the Legionella bacteria to survive. People around these water sources can breathe in the steam, letting those water droplets into their respiratory systems and facilitating an infection. This is the most common way people contract Legionnaires’ disease and Pontiac fever.
  • Aspirating Drinking Water: Though this is a less common way to contract the disease, it is possible to get Legionnaires’ disease by accidentally breathing in drinking water. You may know this as water “going down the wrong pipe.” In these cases, water goes down the trachea, or windpipe, instead of the digestive tract. People with swallowing difficulties are particularly vulnerable to this method of infection.

Both of these methods of infection require a water source of some kind. In man-made systems, the most common and most concerning infection sites include showers and faucets connected to outdated home plumbing systems, poorly-maintained fountain and hot tub systems and even humidifiers. Even emergency home water stores have been linked to outbreaks, as water containers are often kept in warm, dark environments that are ideal for Legionella growth. However, the most abundant sources of Legionella outbreaks are HVAC cooling towers. The reason for this is discussed in more detail in the next section.

the CDC estimates that 10% of identified Legionella infections are travel-related - infographic

The impact of Legionella on water systems is most apparent in the summer and early fall, when infection rates experience a sharp increase. This is primarily because water systems of all types tend to run slightly warmer during these periods, allowing the bacteria to grow. This season is also ideal for international travelers visiting hotels, resorts and other tourist attractions, many of which use HVAC cooling tower systems. This may why be 10 percent of identified Legionella infections are travel-related, as estimated by the CDC.

This may why the CDC estimates that 10 percent of identified Legionella infections are travel-related.

How Do HVAC Cooling Towers Promote Legionella Outbreaks?

HVAC cooling towers lead to more infections than any other source, outpacing exposure due to showering by a factor of 100. Exposure through this source is so common due to the fact that HVAC cooling towers combine the perfect growing conditions for Legionella with an air cycling system and tend to be used in buildings containing hundreds of people at a time.

Essentially, HVAC cooling towers are large air conditioning units for commercial and residential buildings, designed to cycle and cool large quantities of air. The system works by cycling air to pass by a refrigeration unit, which efficiently removes heat from the air. These systems also use a recirculated water system, coming in contact with the refrigerant to remove excess heat and dispose of it by way of evaporation. To keep this water from stagnating, the water is cycled through the system by regularly bleeding and adding fluid, discouraging bacterial growth.

Though HVAC cooling tower systems are useful for cooling air, they are also prime locations for Legionella growth. This is due to the following factors:

  • Temperature: The water in cooling towers is often kept at temperatures around 20°C or 68°F, which is at the lower end of Legionella’s ideal range. If the temperature of the system’s water stays at or around this range, the system becomes an ideal location for Legionella to grow and thrive.
  • Open Systems: While most newer cooling tower systems enclose the system to prevent the drift of water vapor, many older systems don’t take such precautions, making it easy for water vapor to cycle into the air system. Even new systems can leak infected water back into the air if improperly maintained.
  • Stagnation: To ensure that the water does not stagnate, cooling towers regularly cycle their water by bleeding and adding fluid. Though this water cycling discourages bacterial growth, it doesn’t prevent all growth. Mineral buildups and surface defects in the system can create stagnant pockets that are ideal for bacterial growth, and short system shutdowns due to electrical failures or shutoffs can be all that’s needed for Legionella bacteria to grow.
  • Maintenance: Manufacturers and public health officials recommend cleaning and disinfecting cooling towers once annually if they are used year-round and two to four times annually if used seasonally. Failure to appropriately clean and disinfect cooling towers on an appropriate time scale can result in bacterial growth as the system’s water stagnates, creating perfect conditions for an outbreak the next time the system is turned on.

Most of these factors can be prevented by updating existing systems and keeping up with maintenance. You can also employ a water treatment company like Chardon Laboratories to regularly test your system for pathogenic serotypes of Legionella pneumophilia and develop a customized treatment and prevention plan for your application. 

How Do You Prevent Legionella Outbreaks?

It is common to find Legionella in the raw water entering your water systems, but you can fight off colonization with proper planning and equipment. With the prevalence of potential growth sites — and the appearance of Legionella in city water sources like in Flint, Michigan — preventing Legionella outbreaks is more important than ever before. This can be done with a few basic steps recommended by the World Health Organization:

  • Recognize Health-Based Targets and Regulations: Usually set at a national level, these targets and regulations specify the acceptable level of bacteria in any one area. Acceptable levels tend to vary based on the location and context of the infected water source – for example, acceptable levels for a public fountain may not be the same as acceptable levels for a cooling tower or hospital water heater. These Legionella targets and guidelines continue to evolve each year in response to new outbreaks.
  • Implement Water Safety Plans: Also known as “risk management plans,” these procedures pertain to the prevention of outbreaks and involve detailed plans for how to apply and monitor disease prevention measures in water systems. They usually begin with an assessment of the system’s current status and compliance with health-based targets. After this, new systems and control measures, such as disinfectants and environmental controls, can be introduced, and monitoring and management systems can be put in place to ensure proper implementation of the new measures.
  • Surveil Systems Regularly: This involves putting in place monitoring systems and regular water tests to ensure the water source is compliant with health-based targets.

common to find Legionella in raw water entering your water systems but can fight off - infographic

In terms of preventing and controlling Legionella bacteria specifically, facilities can prevent and treat Legionella outbreaks by:

  • Controlling Nutrient Levels: Limiting the amount of organic nutrients in a water system can help control Legionella populations. Design your systems to minimize the accumulation of biofilms, sediment and deposits, reducing the prevalence of nutrients on which the bacteria can feed.
  • Preventing Stagnation: Low flow rates increase the chances of creating a biofilm or deposit, increasing the likelihood of growing bacteria. Regularly flushing low-flow areas and designing water systems to minimize stagnation and remove dead-lags helps eliminate this possibility.
  • Introducing Biocides: In addition to system designs and maintenance procedures, you should use biocides and other chemical treatments to control Legionella populations and the microorganisms on which they feed. However, biocides can only kill what it comes into contact with, so you should use them in tandem with other prevention and control methods.

A combination of all these control measures could help control Legionella growth. However, doing so effectively can be a challenge. That’s why you need a team of experienced water treatment professionals on your side. 

Where Can You Find a Quality Water Treatment Service?

If you’re looking for an industrial and commercial water treatment company, Chardon Laboratories can offer you great service and results.

Our testing procedures will monitor your systems for harmful Legionella outbreaks, identifying the serogroup of the species and the prevalence of the bacterial growth. If we discover that your systems contain over 100 colony-forming units per milliliter of water, we’ll work with you to develop a customized treatment and prevention program to handle Legionella colonization in your cooling tower systems. Our ISO-certified company works to get you results at competitive and transparent prices. We’ll even provide you with hand-delivered products and regular electronic reports so that you can maintain your system more effectively.

At Chardon Labs, we don’t just sell chemicals — we sell clean systems. Contact us today to learn more about our quality water treatment services.

Page Updated September 26, 2017

Portrait of Matt Welsh, the co-president
Matt Welsh
Vice President, Water Consultant at Chardon Labs | Website | + posts

Matt Welsh is the Vice President and Water Consultant at Chardon Labs.  He helps consult a wide range of customers utilizing various methods of water treatment, from chemical to chemical-free approaches, large and small applications, and across a wide range of geographical influences.  With 20 years of water treatment experience, including a wide range of troubleshooting and service in potable water and non-potable HVAC and industrial applications, he is an expert in water treatment chemistry for cooling towers, boilers, and closed-loop systems.


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