Legionella
Overview
 
Legionella is a pathogenic Gram negative bacterium, including species that cause legionellosis
Legionellosis
Legionellosis is a potentially fatal infectious disease caused by gram negative, aerobic bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between , with an optimum temperature...

 or Legionnaires' disease, most notably L. pneumophila
Legionella pneumophila
Legionella pneumophila is a thin, ærobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires' disease.-Characterization:L...

. It may be readily visualized with a silver stain.

Legionella is common in many environments, with at least 50 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 and 70 serogroups
Serotype
Serotype or serovar refers to distinct variations within a subspecies of bacteria or viruses. These microorganisms, viruses, or cells are classified together based on their cell surface antigens...

 identified. The side-chains of the cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

 carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many Gram-negative bacteria.

Legionella acquired its name after a July, 1976 outbreak of a then-unknown "mystery disease" sickened 221 persons, causing 34 deaths.
Encyclopedia
Legionella is a pathogenic Gram negative bacterium, including species that cause legionellosis
Legionellosis
Legionellosis is a potentially fatal infectious disease caused by gram negative, aerobic bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between , with an optimum temperature...

 or Legionnaires' disease, most notably L. pneumophila
Legionella pneumophila
Legionella pneumophila is a thin, ærobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires' disease.-Characterization:L...

. It may be readily visualized with a silver stain.

Legionella is common in many environments, with at least 50 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 and 70 serogroups
Serotype
Serotype or serovar refers to distinct variations within a subspecies of bacteria or viruses. These microorganisms, viruses, or cells are classified together based on their cell surface antigens...

 identified. The side-chains of the cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

 carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many Gram-negative bacteria.

Legionella acquired its name after a July, 1976 outbreak of a then-unknown "mystery disease" sickened 221 persons, causing 34 deaths. The outbreak was first noticed among people attending a convention of the American Legion
American Legion
The American Legion is a mutual-aid organization of veterans of the United States armed forces chartered by the United States Congress. It was founded to benefit those veterans who served during a wartime period as defined by Congress...

 - an association of U.S.
United States armed forces
The United States Armed Forces are the military forces of the United States. They consist of the Army, Navy, Marine Corps, Air Force, and Coast Guard.The United States has a strong tradition of civilian control of the military...

 military veterans. The convention in question occurred in Philadelphia during the U.S. Bicentennial
United States Bicentennial
The United States Bicentennial was a series of celebrations and observances during the mid-1970s that paid tribute to the historical events leading up to the creation of the United States as an independent republic...

 year. This epidemic among U.S. war veterans, occurring in the same city as – and within days of the 200th anniversary of – the signing of the Declaration of Independence
United States Declaration of Independence
The Declaration of Independence was a statement adopted by the Continental Congress on July 4, 1776, which announced that the thirteen American colonies then at war with Great Britain regarded themselves as independent states, and no longer a part of the British Empire. John Adams put forth a...

, 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. See Legionnaires' Disease for full details.

Detection

Legionella is traditionally detected by culture on buffered charcoal yeast extract (BCYE) agar. Legionella requires the presence of cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

 to grow and therefore does not grow on common blood agar media used for laboratory based total viable counts or on site displides. Common laboratory procedures for the detection of Legionella in water concentrate the bacteria (by centrifugation and/or filtration through 0.2 micrometre filters) before inoculation onto a charcoal yeast extract agar containing antibiotics (e.g. glycine vancomycim polymixin cyclohexamide, GVPC) to suppress other flora in the sample. Heat or acid treatment are 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 BCYE containing cysteine, but not on agar without cysteine added. Immunological techniques are then commonly used to establish 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 is that the results can be obtained in a matter of hours rather than the five days required for culture, and that a urine specimen is generally more easily obtained than a sputum specimen. One disadvantage is that the urine antigen test only detects anti-bodies towards Legionella pneumophila; only a culture will detect infection by the other Legionella species.

New techniques for the rapid detection of Legionella in water samples are emerging including the use of polymerase chain reaction
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....

 (PCR) and rapid immunological assays
Immunoassay
An immunoassay is a biochemical test that measures the presence or concentration of a substance in solutions that frequently contain a complex mixture of substances. Analytes in biological liquids such as serum or urine are frequently assayed using immunoassay methods...

. These technologies can typically provide much faster results.

Pathogenesis

Legionella live within amoebae in the natural environment. Legionella species are the causative agent of the human Legionnaires' disease and the lesser form, Pontiac fever
Legionellosis
Legionellosis is a potentially fatal infectious disease caused by gram negative, aerobic bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between , with an optimum temperature...

. Legionella transmission is via aerosols — the inhalation of mist droplets containing the bacteria. Common sources include cooling tower
Cooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...

s, swimming pools (especially in Scandinavian countries), domestic hot-water systems, fountains, and similar disseminators that tap into a public water supply. Natural sources of Legionella include freshwater ponds and creeks. Person-to-person transmission of Legionella has not been demonstrated.

Once inside a host, incubation may take up to two weeks. Initial 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 diarrhea 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 harmful symptoms only in those with a compromised immune system and the elderly. Consequently, it should be actively checked for in the water systems of hospitals and nursing homes. The Texas Department of State Health services provides recommendations for hospitals to detect and prevent the spread of nosocomial infection
Nosocomial infection
A nosocomial infection , also known as a hospital-acquired infection or HAI, is an infection whose development is favoured by a hospital environment, such as one acquired by a patient during a hospital visit or one developing among hospital staff...

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

In the United States, the disease affects between 8,000 to 18,000 individuals a year.

Weaponization

It has been suggested that Legionella could be used as a weapon, and indeed genetic modification of Legionella pneumophila has been shown where the mortality rate in infected animals can be increased to nearly 100%.

Molecular biology

With the application of modern molecular genetic and cell biological techniques, the mechanisms used by Legionella to multiply within macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s are beginning to be understood. The specific regulatory cascades that govern differentiation as well as the gene regulation are being studied. The genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 sequences of five L. pneumophila strains have been published and it is now possible to investigate the whole genome by modern molecular methods. The molecular structure of some of the proven virulence factors of Legionella have been discovered by some researchers. The molecular studies are contributing to the fields of clinical research, diagnosis, treatment, epidemiology, and prevention of disease.

Source control

The most common sources of Legionella and Legionnaires' disease outbreaks are cooling towers (used in industrial cooling water systems), domestic hot water systems,and spas. Additional sources include large central air conditioning systems, fountains, domestic cold water, swimming pools (especially in scandinavian countries and northern ireland) and similar disseminators that draw upon a public water supply. Natural sources include freshwater ponds and creeks. Many governmental agencies, cooling tower manufacturers, and industrial trade organisations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers.

Recent research in the Journal of Infectious Diseases provides evidence that Legionella 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. There were 86 confirmed cases during the outbreak, of which 18 resulted in death. The source of infection was identified as a cooling tower in a petrochemical
Petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

 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.

Several European countries established the European Working Group for Legionella Infections
European Working Group for Legionella Infections
The European Working Group for Legionella Infections was formed in 1986. Its members are scientists with an interest in improving knowledge and information on the epidemiological and microbiological aspects of legionnaires' disease...

 (EWGLI) to share knowledge and experience about monitoring potential sources of Legionella. The EWGLI has published guidelines about the actions to be taken to limit the number of colony-forming units (CFU, that is, live bacteria that are able to multiply) of Legionella per litre:
Legionella bacteria CFU/litreAction 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 re-sampling. 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.
more than 10,000 Implement corrective action. The system should immediately be re-sampled. It should then be "shot dosed" with an appropriate biocide
Biocide
A biocide is a chemical substance or microorganism which can deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means. Biocides are commonly used in medicine, agriculture, forestry, and industry...

, 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.)


According to the paper "Legionella and the prevention of legionellosis," found at the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 website, 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)
    D-value (microbiology)
    In microbiology, D-value refers to decimal reduction time is the time required at a certain temperature to kill 90% of the organisms being studied. Thus after a colony is reduced by 1 D, only 10% of the original organisms remain. The population number has been reduced by one decimal place in the...

     = 2)
  • At 50 °C (122 °F) - 90% die in 80-124 minutes, depending on strain (Decimal reduction time (D)
    D-value (microbiology)
    In microbiology, D-value refers to decimal reduction time is the time required at a certain temperature to kill 90% of the organisms being studied. Thus after a colony is reduced by 1 D, only 10% of the original organisms remain. The population number has been reduced by one decimal place in the...

     = 80-124) - Can survive but do not multiply - Ideal growth range - Growth range
  • Below 20 °C (68 °F) - Can survive but are dormant, even below freezing


Other sources claim alternate temperature ranges:
to 80 °C (176 °F) - Disinfection range - Legionella die within 2 minutes - Legionella die within 32 minutes - Legionella die within 5 to 6 hours to 45 °C (113 °F) - Legionella multiply & below - Legionella are dormant
Control of Legionella growth can occur through chemical or thermal methods. The least expensive and most effective control method is keeping all cold water below 78F and all hot water above 124F. Copper-silver ionization
Copper-silver ionization
thumb|100px|[[Copper]] electron shellthumb|100px|[[Silver]] electron shellCopper-silver ionization is an industrial control and prevention process, approved by the U.S...

 is a heavy metal, systemic toxin that destroys biofilms and slimes that can harbor Legionella over the long term. To date no copper-silver system has had EPA approved efficacy studies resulting in final EPA approval as a biocide. Chlorination with chlorine dioxide
Chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....

 or monochloramine are extremely effective oxidizing biocides. Ultraviolet light is an excellent treatment but it does not leave a residual in the bulk water system. Thermal eradication is a short term marginally effective and expensive method. Ozone is extremely effective oxidizing biocide for cooling towers, fountains and spas treatment.

Chlorine

A very effective chemical treatment is chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

. For systems with marginal issues chlorine will provide effective results at 0.5 ppm residual in the hot water system. For systems with significant Legionella problems a residual of as much as 3 ppm free chlorine is required in the hot water system. This level of chlorine will destroy copper piping within 7 to 10 years.

Copper-silver ionization

Industrial-size copper-silver ionization
Copper-silver ionization
thumb|100px|[[Copper]] electron shellthumb|100px|[[Silver]] electron shellCopper-silver ionization is an industrial control and prevention process, approved by the U.S...

 is approved by the U.S. Environmental Protection Agency for Legionella control and prevention. As long as levels of copper and silver ions are sufficient to perform their disinfection function, disinfection can occur as rapidly as one week. Items that can dramatically impact the levels of copper ions include city water pH, free chlorine, and city water corrosion inhibitors of phosphate and silica.

The US EPA issued a Federal Register Regulation document on September 21, 2007 titled “Pesticide Registration; Clarification for Ion-Generating Equipment” stating that copper silver ionization units must be registered as a biocide. The Federal register document states the following; “Under FIFRA, it is unlawful to sell or distribute any ``pesticide unless it is registered by EPA pursuant to FIFRA section 3.
EPA has authority to register pesticides under FIFRA section 3, and therefore to interpret the terms ``pesticide and ``device for purposes of determining what is and what is not subject to the registration requirements of FIFRA.” “The articles covered by this notice are ion generators that incorporate a substance (e.g., silver or copper) in the form of an electrode, and pass a current through the electrode to release ions of that substance for the purpose of preventing, destroying, repelling, or mitigating a pest (e.g., bacteria or algae). Because these items incorporate a substance or substances that accomplish their pesticidal function, such items are considered pesticides for purposes of FIFRA, and must be registered prior to sale or distribution.”

http://www.epa.gov/oppad001/ion_gen_equip.htm

Chlorine dioxide

Chlorine dioxide has been EPA approved as a primary potable water  disinfectant since 1945. It does not produce any carcinogenic byproducts like chlorine and 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 impacted by pH, or any water corrosion inhibitors like silica or phosphate. Monochloramine is an alternative. Like chlorine and chlorine dioxide, monochloramine is EPA approved as a primary potable water disinfectant. EPA registration requires an EPA biocide label which lists toxicity and other data required by the EPA for all EPA registered biocides. If the product is being sold as a biocide then the manufacturer is legally required to supply a biocide label. And the purcharser is legally required to apply the biocide per the biocide label. 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

Moist heat sterilization

Moist heat sterilization
Moist heat sterilization
Heating an article is one of the earliest forms of sterilization practiced. Moist heat, as the name indicates, utilizes hot air that is heavily laden with water vapour and where this moisture plays the most important role in the process of sterilization....

 (superheating
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...

 to 140 °F (60 °C) and flushing) is a nonchemical treatment that typically must be repeated every 3–5 weeks.

Monitoring

Minimal monitoring guidelines are stated in ACOP L8 in the UK. These are not mandatory however are widely regarded as so. Failure to show monitoring records to at least this standard has resulted in several high profile prosecutions, e.g Nalco + Bulmers - Both could not prove a sufficient scheme to be in place whilst investigating an outbreak, therefore both were fined in the region of £300,000GBP.

Any building within the UK which is subject to HASAW 1974 is required under COSHH and ACOP L8 to have a legionella risk assessment carried out. The report should include a detailed narrative of the site, asset register, simplified schematic drawings (if none available on site), reccomendations on compliance and a proposed monitoring scheme.

Log books should be held on site for a minimum of 5 years. E-logbooks are available, however issues can arise if a site audit is carried out and the auditor cannot access the server for any reason (User isn't set up, someone is on holiday/ill, etc). Electronic logbooks are generally more useful when managing large portfolios, however a duplication is advisable because of the 5 year 'on site / available for inspection' requirement, and therefore kills the 'no paper' argument.

The guidance to the ACOP L8 regulations says that the legionnaires risk assessment should be reviewed at least every 2 years and whenever there is reason to suspect it is no longer valid, such as if you have added to, or modified, your water systems, or if the use of the water system has changed, or if your legionella control measures are no longer working. For a simple system, the risk assessment review may be fairly straight forward, but for more complex systems it may be best to carry out a full legionnaires risk assessment from scratch.

See also

  • Biocide
    Biocide
    A biocide is a chemical substance or microorganism which can deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means. Biocides are commonly used in medicine, agriculture, forestry, and industry...

  • European Working Group for Legionella Infections
    European Working Group for Legionella Infections
    The European Working Group for Legionella Infections was formed in 1986. Its members are scientists with an interest in improving knowledge and information on the epidemiological and microbiological aspects of legionnaires' disease...

  • Environmental microbiology
    Environmental microbiology
    Environmental microbiology is the study of the composition and physiology of microbial communities in the environment. The environment in this case means the soil, water, air and sediments covering the planet and can also include the animals and plants that inhabit these areas...

  • Nosocomial infection
    Nosocomial infection
    A nosocomial infection , also known as a hospital-acquired infection or HAI, is an infection whose development is favoured by a hospital environment, such as one acquired by a patient during a hospital visit or one developing among hospital staff...


External links


Maintenance guidelines

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