Legionella in Cooling Towers - An overview and management plan

What is Legionellosis?

Legionnaires’ disease first garnered public attention in 1976. After attending an American Legion convention at a Philadelphia hotel, 221 people became ill, with 34 dying of a mysterious illness. The U.S. Centers for Disease Control and Prevention (CDC) launched a major investigation, and in 1977 identified the responsible bacterium, naming it Legionella.

Infections caused by Legionella are called Legionellosis and have mild to severe effects. Two diseases caused by Legionella are Legionnaires’ disease and Pontiac Fever. Legionnaires’ disease is a potentially fatal pneumonia, whereas Pontiac Fever is more like a mild flu. While the disease and its cause are well known, the CDC reports that cases of Legionnaires’ disease in the United States have grown by nearly 450 percent since 2000. This may be partly due to more infections, but also to aging population, increased awareness and testing, and other factors.

Symptoms for Pontiac Fever begin a few hours to three days after exposure and last about a week. Legionnaire’s disease symptoms begin 2 to 10 days from exposure. They may include cough, shortness of breath, fever, chills, headaches, muscle aches, and gastrointestinal illness. Patients often require hospitalization. Fatality rate varies, but the overall rate in Europe is 12 percent according to the World Health Organization (WHO).

Inhaling contaminated, aerosolized water droplets less than five microns in diameter is the most common route of exposure. Showerheads and faucets, hot tubs, cooling towers, HVAC systems, water fountains, and other water systems create aerosols that transmit the bacteria. Those most at risk are people over 50 years old, current or former smokers, people with existing lung disease, and those with compromised immune systems.

 

Legionella Bacteria

Legionellae are common throughout the worldwide environment in water and moist soil. While there are numerous species and subspecies of Legionella, only a few cause infections, with the majority resulting from exposure to L. pneumophila.

Legionella prefers warm water for growth, over 20 degrees C (77 degrees F), but below 50 degrees C (122 degrees F). The optimum temperature is 37 degrees C (98.6 degrees F), which is body temperature and the temperature most hot tubs are set at. It multiplies in stagnant water, making facilities with intermittent flows attractive. Cruise ships, hotels, campsites, and schools are highly susceptible for this reason.

In nature, Legionella does not exist in quantities to cause disease. However, small amounts can enter the water distribution system. It can then multiply in the complex water systems of large buildings and other facilities to become infectious. In addition to those noted above, common locations for infection include hospitals, large office complexes, areas around cooling towers, and fountains.

 

 

The Importance of Biofilm

Microorganisms, including Legionellae can adhere to natural and man-made surfaces. As they colonize they form a biofilm, which helps protect them from temperature extremes or biocides.

Biofilms are extremely complex ecosystems and may consist of bacteria, algae, and grazing protozoa. Areas of slow water flow and stagnation encourage biofilm formation.

Water flowing past the biofilm provides nutrients and gas exchange, allowing Legionella to multiply. The biofilm provides stability, making it more difficult to physically remove Legionella and other pathogens, especially on surfaces with scale or corrosion. About 90 percent of the Legionella bacteria are in the biofilm versus the water stream.

Legionellae grown in biofilm are more resistant than those grown in the liquid phase. Research at the Montana State University Center for Biofilm Engineering has also found that as biofilms collect sediment or scale they become brittle and can break off in fragments. When these fragments are inhaled, they are more difficult for the body to clear than single bacteria.

As biofilm grows, protozoans can live within it. Protozoans are single celled animals, and include flagellates, ciliates, and amoebae. Legionella can infect an amoeba, a protozoan species, using the amoeba’s internal materials as nutrients while gaining protection from the outside environment. Legionellae replicate within the amoebae, ultimately exploding and infecting other amoebae, then continuing to multiply.

To make things worse, Legionella that has grown within an amoeba may be protected from adverse conditions. Per a May 2013 article in the journal Virulence, “Cellular microbiology and molecular ecology of Legionella—amoeba interaction,” when environmental conditions are unfavorable, amoeba can form into a cyst, protecting Legionella. The article also notes that “bacteria grown in amoeba have changes in biochemistry, physiology, and virulence potential” including better antibiotic and chemical resistance.

Industries and companies are responsible for minimizing risks posed by the growth of Legionella in their water systems thus preventing Legionellosis.

 

Regulatory Landscape

Regulations for preventing Legionellosis are difficult to encapsulate. The United Kingdom was a leader in this respect, implementing a stringent Code of Conduct after a major outbreak in the 1980’s. The European Technical Guidelines for the Prevention, Control and Investigation of Infections Caused by Legionella Species is used as referral document throughout Europe. While individual countries may have different specific requirements, each has required methods to minimize risk, control Legionella growth, and document actions taken.

Guidelines in the United States (U.S.) are issued by the CDC, but there are currently no regulations. Some states or cities have adopted sections of the guidelines as law. Affected
industries have implemented standards supported by the CDC, which offers a toolkit called Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings: A Practical Guide to Implementing Industry Standards. Other countries, like Indonesia, are now considering regulations for the control and prevention of Legionellosis.

 

Water Safety Plans

The guidelines above include development of a written Water Safety Plan (WSP) or water management program for each affected facility. Companies must perform a survey and risk assessment, looking at every link in the causative chain for Legionellosis. Once the risk assessment is complete they must address all the applicable issues. Other items in the WSP include training requirements for employees, documentation, and procedures to follow if an outbreak occurs. Each WSP is unique to its facility.

Items required in the WSP may include maintaining cold water taps below 15 degrees C (59 degrees F) and above 50 degrees C (122 degrees F), flushing stagnant lines, adding disinfectants, and preventing corrosion and biofilm buildup.

 

Breaking the Causative Chain

While regulations, standards, and guidelines for preventing Legionellosis have been in effect for over 30 years, the number of outbreaks continues to grow. Recent U.S. cases include a July 2018 outbreak resulting in 22 people with Legionnaire’s disease and one death. And in August 2018, an outbreak in New Hampshire left 14 people sick and one person deceased. In Italy, a July 2018 outbreak with 26 cases claimed three lives.

Clearly, the challenge of preventing this deadly disease is still ongoing. Each link in the causative chain must be addressed. Companies must find and cut the chain at its weakest link.

 

How to implement a Legionella management solution

In order to cause infection, Legionella must be allowed to multiply and gain sufficient numbers. By controlling and minimizing Legionella proliferation, facility owners greatly reduce the risk of an outbreak.

Biofilm hosts the clear majority of Legionella in a water system—about 90 percent as noted previously. Also, Legionella grown in biofilm is more resistant to control methods. Heavy biofilm growth also supports amoebae, in which Legionella can strengthen and grow to the point of great multiplication and explosion.

 

By controlling the formation of biofilm, the causative chain of Legionellosis can be broken

 

Biofilm prevention and removal should be part of a general microbial control program. Stopping the multiplication of Legionella does the same for other pathogens. For example, Naegleria fowleri, the “brain-eating amoeba,” or Salmonella, which causes 1.2 million gastrointestinal illnesses in the U.S. each year, could be reduced.

Innovative Water Care is one of the world’s leading biocidal companies, with a presence in North America, Europe, Asia, Africa, South America, and Australia. Our Water Care team collectively has hundreds of years of industrial water treatment experience. With a deep understanding of Legionella and other pathogens, we are experts in controlling the multiplication of waterborne bacteria.

Biofilms are very complex, dynamic systems. Preventing and removing them requires a high level of expertise. Many of our employees have worked in the industrial water industry and understand the systems where Legionella growth occurs.

 

Reducing the Risk of Legionellosis

We also keep up with regulations on a worldwide basis, and have developed an extensive portfolio of products to greatly reduce the potential for Legionellosis, with a three-pronged approach

1. Prevent biofilm formation. This is the key to breaking the causative chain of Legionellosis. Our patented Aphelion® Stabilizer allows chlorine to penetrate the established biofilm. This technology allows the disinfectant to bypass the protective shield typically provided by the biofilm.

2. Enhance the Legionella-inhibiting effectiveness of oxidizing halogen-based disinfectants. Aphelion® technology provides a stabilization and controlled-release mechanism that assures free halogen at all places.

3. Use Non-Oxidizing biocides for Legionella control. In emergency cases, we have 19 products with proven effectiveness against Legionella pneumophila. Included within the group of 19 Innovative Water Care products approved for various applications are Bardac 22Isocil RW 1.5% and Lonzabac 12. These products were tested using the European method according EN13623. (This method may not be recognized in all countries). If the first two steps are utilized, this third method of control may not be needed.

 

Engage Technical Expertise

Using the help of technical experts saves companies time and money while helping to prevent a tragic Legionellosis outbreak. Our team has people around the world with the knowledge and experience to help companies break the chain and reduce the risk of this and other deadly diseases.

To find out more, or to speak with one of our representatives, click this link to the Contact Us form.

 

 

 

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Recommended resources:

European technical guidelines for the prevention, control and investigation of infections caused by Legionella species

ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems

Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings - Center for Disease Control and Prevention