The genus
Legionella is a pathogenic group of
gram negative bacterium, that includes the species
L. pneumophila, which causes
Legionnaires Disease and
L.longbeachae which causes
Pontiac Fever.
[1][2] It may be readily visualized with a
silver stain.
Legionella is common in many environments, including soil and aquatic systems, with at least 50
species and 70
serogroups identified.
The
side-chains of the
cell wall 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—an association of
U.S. military
veterans. The convention in question occurred in
Philadelphia during the
U.S. Bicentennial 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, was widely publicized and caused great concern in the United States.
[3] On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named
Legionella. See
Legionnaires' Disease for full details.
Detection[edit]
Legionella is traditionally detected by culture on buffered charcoal yeast extract (BCYE) agar.
Legionella requires the presence of
cysteine and iron to grow and therefore 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
[4] 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.
Although the plating method is quite specific for most species of Legionella, one study has shown that a coculture method that accounts for the close relationship with amoebas may be more sensitive since it can detect the presence of the bacteria even when masked by its presence inside the amoeba.
[5] Consequently, the true clinical and environmental prevalence of the bacteria is likely to be underestimated due to false negatives inherent in the current lab methodology.
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. Disadvantages are that the urine antigen test only detects antigen 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 of LD.
[6]
New techniques for the rapid detection of
Legionella in water samples are emerging including the use of
polymerase chain reaction (PCR) and
rapid immunological assays. These technologies can typically provide much faster results.
Pathogenesis[edit]
Legionella live within amoebae in the natural environment.
[7] Upon inhalation the bacteria can infect alveolar macrophages. subverting the normal host cell machinery to create a niche where the bacteria can replicate. This results in
Legionnaires' disease and the lesser form,
Pontiac fever.
Legionella transmission is airborne via respiratory droplets containing the bacteria. Common sources include
cooling towers, 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.
[8]
Once inside a host, incubation may take 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 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 due to legionella.
[9] 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.
[10]
In the United States, the disease affects between 8,000 to 18,000 individuals a year.
[3]</ref>
Weaponization[edit]
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%.
[11][12][13]
Molecular biology[edit]
With the application of modern molecular genetic and cell biological techniques, the mechanisms used by
Legionella to multiply within
macrophages are beginning to be understood. The specific regulatory cascades that govern
differentiation as well as the gene regulation are being studied. The
genome sequences of six
L. pneumophila strains have been published and it is now possible to investigate the whole genome by modern molecular methods. It has been discovered that Legionella is a genetically diverse species with 7-11% of genes strain specific. The molecular function of some of the proven virulence factors of Legionella have been discovered by some researchers.
[14] Molecular studies are contributing to the fields of clinical research, diagnosis, treatment, epidemiology, and prevention of disease.
[2]
Source control[edit]
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 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.
[15]
Several European countries established the
European Working Group for Legionella Infections (EWGLI)
[16] 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/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 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, 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,"
[17] found at the
World Health Organization 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) = 2)
- At 50 °C (122 °F) - 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80-124)
- 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 but are dormant, even below freezing
Other sources
[18][19][20] claim alternate temperature ranges:
- 60 to 70 °C (140 to 158 °F) to 80 °C (176 °F) - Disinfection range
- 66 °C (151 °F) - Legionella die within 2 minutes
- 60 °C (140 °F) - Legionella die within 32 minutes
- 55 °C (131 °F) - Legionella die within 5 to 6 hours
- 20 °C (68 °F) to 45 °C (113 °F) - Legionella multiply
- 20 °C (68 °F) & 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 25°C (78°F) and all hot water above 51°C (124°F).
Copper-silver ionization 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 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.
[21]
Chlorine[edit]
A very effective chemical treatment is
chlorine. For systems with marginal issues chlorine will provide effective results at 0.5 ppm
[citation needed] 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.
Industrial Size Copper-Silver ionization[edit]
Industrial-size
copper-silver ionization is recognized by the
U.S. Environmental Protection Agency and WHO for
Legionella control and prevention. When copper and silver ions maintained, when taking into account both water flow and overall water usage, the disinfection function within all of a facilities water distribution network will occur 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 0-100 VDC are but a few of the required features for proper Legionella control and prevention. Swimming pool ion generators are not engineered for facility potable water Legionella control and prevention.
Ionization is an effective industrial control and prevention process to control
Legionella in potable water distribution systems found in health facilities, hotels, nursing homes and most large buildings. CuAg is not intended for cooling towers because of pH levels over 8.6 that cause ionic copper to precipitate. In 2003 researchers that heavily support ionization developed a four validation process that supports their research on ionization. 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.
[22] Additional studies indicate ionization is superior to thermal eradication.
Chlorine dioxide[edit]
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.
Vaccine research[edit]
There is no vaccine for legionellosis, and antibiotic
prophylaxis is not effective. Any licensed vaccine for humans in the US is most probably still many years away. Vaccination studies using heat-killed or acetone-killed cells have been carried out, and guinea pigs were challenged intraperitoneally or by using the aerosol model of infection. Both vaccines were shown to give moderately high levels of protection. Protection was found to be dose dependent and correlated with antibody levels as measured by enzyme-linked immunosorbent assay to an outer membrane antigen and by indirect
immunofluorescence to heat-killed cells.
Moist heat sterilization[edit]
Moist heat sterilization (
superheating to
140 °F (60 °C) and flushing) is a nonchemical treatment that typically must be repeated every 3–5 weeks.
Monitoring[edit]
Minimal monitoring guidelines are stated in ACOP L8 in the UK. These are not mandatory however are widely regarded as so. An ACOP is an Approved Code of Practice which an employer or property owner must follow, or achieve the same result. 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. Important case law in this area is R v Trustees of the Science Museum 3 All ER 853, (1993) 1 WLR 1171
[24]
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), recommendations 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 requirements of the L8 ACOP and 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.
See also[edit]
References[edit]
- Jump up ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- ^ Jump up to: a b Heuner K, Swanson M (editors). (2008). Legionella: Molecular Microbiology. Caister Academic Press. isbn = 978-1-904455-26-4.
- Jump up ^ Lawrence K. Altman (August 1, 2006). "In Philadelphia 30 Years Ago, an Eruption of Illness and Fear". New York Times.
- Jump up ^ ISO 11731-2:2004 Water quality -- Detection and enumeration of Legionella -- Part 2: Direct membrane filtration method for waters with low bacterial counts
- Jump up ^ La Scola B, Mezi L, Weiller PJ, and Raoult1 D (2001). "Isolation of Legionella anisa Using an Amoebic Coculture Procedure". J Clin Microbiol. 39(1): 365–6. doi:10.1128/JCM.39.1.365-366.2001. Retrieved 2013-06-28.
- Jump up ^ Trends in legionnaires disease, 1980-1998: declining mortality and new patterns of diagnosis. Benin AL; Benson RF; Besser RE. Clin Infect Dis November 1, 2002;35(9):1039-46. Epub October 14, 2002.
- Jump up ^ Swanson M, Hammer B (2000). "Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages". Annu Rev Microbiol 54: 567–613. doi:10.1146/annurev.micro.54.1.567. PMID 11018138.
- Jump up ^ Winn, W.C. Jr. (1996). Legionella (In: Baron's Medical Microbiology, Baron, S. et al., eds. (4th ed.). University of Texas Medical Branch. ISBN 0-9631172-1-1. (via NCBI Bookshelf)
- Jump up ^ Report of the Texas Legionnaires' Disease Task Force, Texas Department of State Health Services [1]
- Jump up ^ Infection Control and Hospital Epidemiology, July 2007, Vol. 28, No. 7, "Role of Environmental Surveillance in Determining the Risk of Hospital-Acquired Legionellosis: A National Surveillance Study With Clinical Correlations" [2]
- Jump up ^ http://www.aina.org/news/20081201063837.htm
- Jump up ^ Gilsdorf et al., Clinical Infectious Diseases 2005; 40 p1160–1165 "New Considerations in Infectious Disease Outbreaks: The Threat of Genetically Modified Microbes" http://cid.oxfordjournals.org/content/40/8/1160.full
- Jump up ^ http://www.homelandsecurity.org/journal/Interviews/PopovInterview_001107.htm
- Jump up ^ Raychaudhury S, Farelli JD, Montminy TP, Matthews M, Ménétret JF, Duménil G, Roy CR, Head JF, Isberg RR, Akey CW (Apr 2009). "Structure and function of interacting IcmR-IcmQ domains from a Type IVb secretion system in Legionella pneumophila". Structure 17 (4): 590–601. doi:10.1016/j.str.2009.02.011. PMC 2693034. PMID 19368892.
- Jump up ^ Nguyen, T.; Ilef, D.; Jarraud, S.; Rouil, L.; Campese, C.; Che, D.; Haeghebaert, S.; Ganiayre, F.; Marcel, F.; Etienne, J.; Desenclos, J. (2006). "A community-wide outbreak of legionnaires disease linked to industrial cooling towers—how far can contaminated aerosols spread?". Journal of Infectious Diseases 193 (1): 102–11. doi:10.1086/498575. PMID 16323138.
- Jump up ^ "European Working Group for Legionella Infections".
- Jump up ^ "LEGIONELLA and the prevention of legionellosis".
- Jump up ^ "Safe Hot Water Temperature".
- Jump up ^ "Controlling Legionella in Domestic Hot Water Systems".
- Jump up ^ "Employers Guide to the control of Legionella".
- Jump up ^ Hayes, John. "Copper/silver ionization gaining approval". Professional Carwashing & Detailing 25 (12).
- Jump up ^ Stout & Yu 2003 "(1) Demonstrated efficacy of Legionella eradication in vitro using laboratory assays, (2) anecdotal experiences in preventing legionnaires’ disease in individual hospitals, (3) controlled studies in individual hospitals, and (4) validation in confirmatory reports from multiple hospitals during a prolonged time."
- Jump up ^ www.hse.gov.uk/chemicals/.../legionella-09/law-and-legionella.pdf
http://www.who.int/water_sanitation_health/emerging/legionella.pdf
External links[edit]
Maintenance guidelines[edit]
