The purpose of this document is to provide an overview of Legionella, its detection, significance, and treatment.

What is Legionella?

Legionella is a genus of pathogenic gram-negative bacteria that includes the species L. pneumophila, causing legionellosis (all illnesses caused by Legionella) including a pneumonia-type illness called Legionnaires’ disease and a mild flu-like illness called Pontiac fever.

Legionella acquired its name after an outbreak in 1976, of a then-unknown “mystery disease”, sickened 221 people, causing 34 deaths. The outbreak was first noticed among attendees at a convention of the American Legion—an association of U.S. military veterans.

The disease was widely publicized and caused great concern in the United States. On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named Legionella.

Where is Legionella found?

It is common in many environments, including soil and aquatic systems, with at least 50 species and 70 serogroups were identified. These bacteria, however, are not transmissible from person to person, furthermore, most people exposed to the bacteria do not become ill. Most outbreaks are traced to poorly maintained cooling towers.

Legionella species typically exist in nature at low concentrations, in groundwater, lakes, and streams. They reproduce after entering man-made equipment, given the right environmental conditions. In the United States, the disease affects between 8,000 and 18,000 individuals a year.

Documented sources include cooling towers, swimming pools, domestic water systems, showers, ice-making machines, refrigerated cabinets, whirlpool spas, hot springs, fountains, dental equipment, soil, automobile windshield washer fluid, industrial coolant, and wastewater treatment plants.

How is Legionella transmitted?

The largest and one of the most common sources of Legionnaires’ disease outbreaks are cooling towers (heat rejection equipment used in air conditioning and industrial cooling water systems) primarily because of the risk for widespread circulation. Many governmental agencies, cooling tower manufacturers, and industrial trade organizations have developed design and maintenance guidelines for controlling the growth and proliferation of Legionella within cooling towers.

Research in the Journal of Infectious Diseases (2006) provided evidence that L. pneumophila, the causative agent of Legionnaires’ disease, can travel at least 6 km from its source by airborne spread. It was previously believed that transmission of the bacterium was restricted to much shorter distances.

A team of French scientists reviewed the details of an epidemic of Legionnaires’ disease that took place in Pas-de-Calais, northern France, in 2003–2004. Of 86 confirmed cases during the outbreak, 18 resulted in death.

The source of infection was identified as a cooling tower in a petrochemical plant, and an analysis of those affected in the outbreak revealed that some infected people lived as far as 6–7 km from the plant.

Not only are Legionella spp. present in man-made water systems and infrastructure, but this bacteria also lives in natural bodies of water, such as lakes and rivers.

Weather patterns and other environmental factors may increase the risk of Legionella outbreaks; a study in Minnesota, USA, using outbreak information from 2011 to 2018 showed precipitation as having the greatest effect of increasing the risk of Legionella exposure when taking into account other environmental factors (temperature, relative humidity, land use and age of infected person).

Weather patterns heavily relate to the established infrastructure and water sources, especially in urban settings. In the US, most cases of Legionella infection have occurred in the summertime, though they were likely more associated with rainfall and humidity than summer temperatures.

Severe rain patterns can increase the risk of water source contamination through flooding and unseasonable rains; therefore, natural disasters, especially those associated with climate change, may increase the risk of exposure to Legionella.

Legionella transmission is via inhalation of water droplets from a contaminated source that has allowed the organism to grow and spread (e.g., cooling towers). Transmission also occurs less commonly via aspiration of drinking water from an infected source. Person-to-person transmission has not been demonstrated,[4] though it could be possible in rare cases.

How is Legionella detected?

Legionella may be visualized with a silver stain or cultured in cysteine-containing media such as agar. Legionella is traditionally detected by culture on buffered charcoal yeast extract agar. It requires the presence of cysteine and iron to grow, so does not grow on common blood agar media used for laboratory-based total viable counts or on-site dipslides.

Common laboratory procedures for the detection of Legionella in water concentrate the bacteria (by centrifugation and/or filtration through 0.2-μm filters) before inoculation onto a charcoal yeast extract agar containing selective agents (e.g. glycine, vancomycin, polymixin, cyclohexamide, GVPC) to suppress other flora in the sample. Heat or acid treatment is also used to reduce interference from other microbes in the sample.

After incubation for up to 10 days, suspect colonies are confirmed as Legionella if they grow on buffered charcoal yeast extract agar containing cysteine, but not on agar without cysteine added. Immunological techniques are then commonly used to determine the species and/or serogroups of bacteria present in the sample.

Many hospitals use the Legionella urinary antigen test for initial detection when Legionella pneumonia is suspected. Some of the advantages offered by this test are that the results can be obtained in hours rather than the several days required for culture and that a urine specimen is generally more easily obtained than a sputum specimen.

Disadvantages are that the urine antigen test only detects antigens of Legionella pneumophila serogroup 1 (LP1); only a culture will detect infection by non-LP1 strains or other Legionella species and that isolates of Legionella are not obtained, which impairs public health investigations of outbreaks.

New techniques for the rapid detection of Legionella in water samples have been developed, including the use
of polymerase chain reaction and rapid immunological assays. These technologies can typically provide much faster
results.

Public-health surveillance has demonstrated increasing proportions of drinking water–associated outbreaks, specifically in
healthcare settings.

What are the risks of a Legionella infection?

Upon inhalation, the bacteria can infect alveolar macrophages, where they can replicate. This results in Legionnaires’ disease and the less severe illness Pontiac fever. Once inside a host, the incubation period may be up to two weeks. Prodromal symptoms are flu-like, including fever, chills, and dry cough.

Advanced stages of the disease cause problems with the gastrointestinal tract and the nervous system and lead to diahorrea and nausea. Other advanced symptoms of pneumonia may also present.

However, the disease is generally not a threat to most healthy individuals, and tends to lead to severe symptoms more often in immunocompromised hosts and the elderly.

Consequently, the water systems of hospitals and nursing homes should be periodically monitored.

According to Infection Control and Hospital Epidemiology, hospital-acquired Legionella pneumonia has a fatality rate of
28%, and the source is the water distribution system.

A biofilm may also be considered a hydrogel, which is a complex polymer that contains many times its dry weight in water. Biofilms are not just bacterial slime layers but biological systems; the bacteria organize themselves into a coordinated functional community.

Biofilms can attach to a surface such as pipes, a tooth or rock, and may include a single species or a diverse group of microorganisms. Subpopulations of cells within the biofilm differentiate to perform various activities for motility, matrix production, and sporulation, supporting the overall success of the biofilm.

The biofilm bacteria can share nutrients and are sheltered from harmful factors in the environment, such as desiccation, antibiotics, and a host body’s immune system. A biofilm usually begins to form when a free-swimming bacterium attaches to a surface.

The formation of biofilm within a water reticulation system complicates the treatment of that system in that the biofilm provides a haven for microbes and bacteria and provides a barrier to eradication methodologies. Attempts to rid a water reticulation system of Legionella will require long-term treatment to break down the biofilm.

Treatment of a reticulation system will often lead to an initial increase in the quantitative presence of Legionella when it is exposed and freed up from the biofilm, and released into the water stream.

For the most practical intents and purposes, Chlorine Dioxide is the best option for Legionella control and biofilm removal
over the long term.

Biofilm management is therefore essential for the eradication of Legionella and its resurgence. Great care must be taken
to ensure the concentration levels are kept within acceptable limits especially if there is a Dialysis service present.

High concentrations of Chlorine are severely corrosive under conditions of high heat and pressure. Autoclave water supply must be treated with Granular Activated Carbon to effectively remove residual Chlorine.

Patients undergoing Dialysis treatment are highly susceptible to Chlorine or its derivatives. The water supply to Renal unit Reverse Osmosis systems has to be treated with Granular Activated Carbon to remove all traces of Chlorine. Pure water supply for Dialysis must be tested before every Dialysis shift for residual chlorine.

Water Reticulation and Storage
To prevent stagnation, biofilm development and maintain a significant flow velocity within the reticulation system care should be taken as follows:

• A high rate of flow is preferable to help prevent bio-film development and scour pipe surfaces.>2m/s
• Dead-end legs in the reticulation system must be avoided and rectified if present. Dead volume must be kept to a
  minimum.
• Storage systems must not present an opportunity for dead volume within the storage system.
• Multiple storage tanks must be configured correctly with water supply shared equally across all storage tanks from the top of the tank.
• Water draw must be drawn equally from the bottom of each storage tank. This will ensure crossflow within all tanks and prevent dead volume and stagnation.

Water Treatment Methods
Control of Legionella growth can occur through chemical, thermal, or ultraviolet treatment methods.

• Heat
  The more expensive option is temperature control—i.e., keeping all cold water below 25 °C (77 °F) and all hot water
  above 51 °C (124 °F). The high cost incurred with this method arises from the extensive retrofitting required for existing
  complex distribution systems in large facilities and the energy cost of chilling or heating the water and maintaining the
  required temperatures at all times and at all distal points within the system.
  Temperature affects the survival of Legionella as follows:
• Above 70 °C (158 °F) – Legionella dies almost instantly.
• At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
• At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes)
• 48 to 50 °C (118 to 122 °F) – can survive but do not multiply.
• 32 to 42 °C (90 to 108 °F) – ideal growth range
• 25 to 45 °C (77 to 113 °F) – growth range
• Below 20 °C (68 °F) – can survive, even below freezing, but are dormant.
  Other temperature sensitivity:
• 60 to 70 °C (140 to 158 °F) to 80 °C (176 °F) – Disinfection range
• 66 °C (151 °F) – Legionella dies within 2 minutes.
• 60 °C (140 °F) – Legionella dies within 32 minutes.
• 55 °C (131 °F) – Legionella dies within 5 to 6 hours.
  Water can be monitored in real-time with sensors.
• Chlorine
  A very effective chemical treatment is chlorine. For systems with marginal issues, chlorine provides effective results at

0.5 ppm residual in the hot water system. For systems with significant Legionella problems, temporary shock
chlorination—where levels are raised to higher than 2 ppm for a period of 24 hours or more and then returned to 0.5
ppm—may be effective. Hyperchlorination can also be used where the water system is taken out of service and the
chlorine residual is raised to 50 ppm or higher at all distal points for 24 hours or more. The system is then flushed and
returned to 0.5 ppm chlorine prior to being placed back into service. These high levels of chlorine penetrate biofilm, killing
both the Legionella bacteria and the host organisms. Annual hyperchlorination can be an effective part of a
comprehensive Legionella preventive action plan. Extreme caution is advised if a Dialyses service is active on site.
Chlorine removal is imperative for Dialyses and heat sterilisation.

• Copper-silver ionization
  Industrial-sized copper-silver ionization is recognized by the U.S. Environmental Protection Agency and WHO
  for Legionella control and prevention. Copper and silver ion concentrations must be maintained at optimal levels, taking
  into account both water flow and overall water usage, to control Legionella. The disinfection function within all of a facility’s
  water distribution network occurs within 30 to 45 days. Key engineering features such as 10 amps per ion chamber cell
  and automated variable voltage outputs having no less than 100 VDC are but a few of the required features for
  proper Legionella control and prevention, using a specific, nonreferenced copper-silver system. Swimming pool ion
  generators are not designed for potable water treatment.

In any case, any facility or public water system using copper-silver for disinfection should monitor its copper and silver ion concentrations to ensure they are within intended levels – both minimum and maximum. Further, no current standards for silver in the EU and other regions allow the use of this technology.

Copper-silver ionization is an effective process to control Legionella in potable water distribution systems found in health facilities, hotels, nursing homes, and most large buildings. However, it is not intended for cooling towers because of pH levels greater than 8.6, which causes ionic copper to precipitate.

Furthermore, tolyl triazole, a common additive in cooling water treatment, could bind the copper making it ineffective. Ionization became the first such hospital disinfection process to have fulfilled a proposed four-step modality evaluation; by then, it had been adopted by over 100 hospitals. Additional studies indicate ionization is superior to thermal eradication.

• Chlorine dioxide
  Chlorine dioxide has been approved by the U.S. Environmental Protection Agency as a primary disinfectant of potable
  water since 1945. Chlorine dioxide does not produce any carcinogenic byproducts like chlorine when used in the
  purification of drinking water that contains natural organic compounds such as humic and fulvic acids; chlorine tends to
  form halogenated disinfection byproducts such as trihalomethanes. Drinking water containing such disinfection byproducts
  has been shown to increase the risk of cancer.
  
• ClO2 works differently from chlorine; its action is one of pure oxidation rather than halogenation, so these halogenated byproducts are not formed. Chlorine dioxide is not a restricted heavy metal like copper. It has proven excellent control
  of Legionella in cold and hot water systems and its ability as a biocide is not affected by pH, or any water corrosion
  inhibitors such as silica or phosphate.
• However, it is ‘quenched’ by metal oxides, especially manganese and iron. Metal
  oxide concentrations above 0.5 mg/L may inhibit its activity. Monochloramine is an alternative. Like chlorine and chlorine
  dioxide, monochloramine is approved by the Environmental Protection Agency as a primary potable water disinfectant.
  When first applied to a system, chlorine dioxide can be added at disinfection levels of 2 ppm for 6 hours to clean up a
  system. This will not remove all biofilm but will effectively remediate the system of Legionella.
  Chlorine dioxide is a volatile gas and hazardous as it is unstable and may explode when in storage. To mitigate this risk
  CLO2 is manufactured on site and fed directly into the water reticulation system at a concentration of .2ppm. CLO2 is highly
  soluble and readily dissolves into water. An alternative short-term (Acute) treatment via CLO2 tablets dissolved into water
  storage tanks is an alternative to expensive capital-intensive equipment required for its onsite generation.
• Moist heat sterilization
  Moist heat sterilization (superheating to 140 °F (60 °C) and flushing) is a nonchemical treatment that typically must be
  repeated every 3–5 weeks.
• Ultraviolet
  Ultraviolet light, in the range of 200 to 300 nm, can inactivate Legionella. According to a review by the US EPA,[42] three log (99.9%) inactivation can be achieved with a dose of less than 7 mJ/cm2

Water testing and European regulatory standards.

Several European countries established the European Working Group for Legionella Infections to share knowledge and experience about monitoring potential sources of Legionella.

The working group has published guidelines about the actions to be taken to limit the number of colony-forming units (that is, live bacteria that can multiply) of Legionella per litre:

Legionella bacteria
CFU/litre
Action required (35 samples per facility are required, including 20 water and 10 swabs)
1000 or less System under control
more than 1000
up to 10,000

Review program operation:

The count should be confirmed by immediate resampling. If a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions.

Implement corrective action:

The system should immediately be resampled. It should then be “shot dosed” with an appropriate biocide, as a precaution. The risk assessment and control measures should be reviewed to identify remedial actions. (150+ CFU/mL in healthcare facilities or nursing homes require immediate action.)

Conclusion

Legionella poses a significant risk to compromised individuals specifically in the healthcare industry. Regular testing for Legionella and action on positive test results is imperative.

For practical intents, it is proposed to treat the system acutely with Chlorine dioxide tablets and the placement of Ultraviolet sanitizers at specific sites testing positive for Legionella.

Should the infection persist and not abate then chronic treatment of the entire water supply is advocated. The installation of a Chlorine dioxide generator is thus required.

The undersigned is available for assistance and further information upon request.

Mark Pretorius
CEO of Marlin Technologies