{{Short description|Pathogenic genus of Gram-negative bacteria}}{{Automatic taxobox | image = Legionella_Plate_01.png | image_caption = ''Legionella'' sp. under UV light | parent_authority = Brenner ''et al.'' 1979 | taxon = Legionella | authority = Brenner ''et al.'' 1979 | subdivision_ranks = Species | subdivision = {{ubl |''Legionella adelaidensis''<ref name=Legionella>{{cite journal |last1=Parte |first1=A.C. |title=Legionella |website=LPSN |url=https://lpsn.dsmz.de/genus/legionella}}</ref> |''Legionella anisa''<ref name=Legionella/> |''Legionella beliardensis''<ref name=Legionella/> |''Legionella birminghamensis''<ref name=Legionella/> |''Legionella bozemanae''<ref name=Legionella/> |''Legionella brunensis''<ref name=Legionella/> |''Legionella busanensis''<ref name=Legionella/> |''Legionella cardiaca''<ref name=Legionella/> |''Legionella cherrii''<ref name=Legionella/> |''Legionella cincinnatiensis''<ref name=Legionella/> |''Legionella clemsonensis''<ref>{{cite journal |title=Legionella clemsonensis sp. nov.: a green fluorescing Legionella strain from a patient with pneumonia |first1=Allison |last1=Palmer |first2=Joseph |last2=Painter |first3=Hayley |last3=Hassler |first4=Vincent P. |last4=Richards |first5=Terri |last5=Bruce |first6=Shatavia |last6=Morrison |first7=Ellen |last7=Brown |first8=Natalia A. |last8=Kozak-Muiznieks |first9=Claressa |last9=Lucas |first10=Tamara L. |last10=McNealy |date=1 October 2016 |journal=Microbiol Immunol |volume=60 |issue=10 |pages=694–701 |doi=10.1111/1348-0421.12439 |pmid = 27619817 |s2cid=3331351|doi-access=free }}</ref> |''Legionella donaldsonii''<ref name=Legionella/> |''Legionella drancourtii''<ref name=Legionella/> |''Legionella dresdenensis''<ref name=Legionella/> |''Legionella drozanskii''<ref name=Legionella/> |''Legionella dumoffii''<ref name=Legionella/> |''Legionella erythra''<ref name=Legionella/> |''Legionella fairfieldensis''<ref name=Legionella/> |''Legionella fallonii''<ref name=Legionella/> |''Legionella feeleii''<ref name=Legionella/> |''Legionella geestiana''<ref name=Legionella/> |''Legionella'' genomospecies 1 |''Legionella gormanii''<ref name=Legionella/> |''Legionella gratiana''<ref name=Legionella/> |''Legionella gresilensis''<ref name=Legionella/> |''Legionella hackeliae''<ref name=Legionella/> |''Legionella impletisoli''<ref name=Legionella/> |''Legionella israelensis''<ref name=Legionella/> |''Legionella jamestowniensis''<ref name=Legionella/> |''Candidatus'' ''Legionella jeonii'' |''Legionella jordanis''<ref name=Legionella/> |''Legionella lansingensis''<ref name=Legionella/> |''Legionella londiniensis''<ref name=Legionella/> |''Legionella longbeachae''<ref name=Legionella/> |''Legionella lytica''<ref name=Legionella/> |''Legionella maceachernii''<ref name=Legionella/> |''Legionella maioricensis''<ref name=Legionella/> |''Legionella massiliensis''<ref name=Legionella/> |''Legionella micdadei''<ref name=Legionella/> |''Legionella monrovica''<ref name=Legionella/> |''Legionella moravica''<ref name=Legionella/> |''Legionella nagasakiensis''<ref name=Legionella/> |''Legionella nautarum''<ref name=Legionella/> |''Legionella norrlandica''<ref name=Legionella/> |''Legionella oakridgensis''<ref name=Legionella/> |''Legionella parisiensis''<ref name=Legionella/> |''Legionella pittsburghensis''<ref name=Legionella/> |''Legionella pneumophila''<ref name=Legionella/> |''Legionella quateirensis''<ref name=Legionella/> |''Legionella quinlivanii''<ref name=Legionella/> |''Legionella rowbothamii''<ref name=Legionella/> |''Legionella rubrilucens''<ref name=Legionella/> |''Legionella sainthelensi''<ref name=Legionella/> |''Legionella santicrucis''<ref name=Legionella/> |''Legionella shakespearei''<ref name=Legionella/> |''Legionella spiritensis''<ref name=Legionella/> |''Legionella steelei''<ref name=Legionella/> |''Legionella steigerwaltii''<ref name=Legionella/> |''Legionella saoudiensis''<ref name=Legionella/> |''Legionella taurinensis''<ref name=Legionella/> |''Legionella thermalis''<ref name=Legionella/> |''Legionella tucsonensis''<ref name=Legionella/> |''Legionella tunisiensis''<ref name=Legionella/> |''Legionella wadsworthii''<ref name=Legionella/> |''Legionella waltersii''<ref name=Legionella/> |''Legionella worsleiensis''<ref name=Legionella/> |''Legionella yabuuchiae''<ref name=Legionella/> |''Legionella bononiensis''<ref name=Legionella/> }} }}
'''''Legionella''''' is a genus of Gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. Most Legionella species are intracellular pathogens whose primary hosts are amoebae, however many ''Legionella'' are accidental pathogens of humans<ref>{{cite journal |last1=Wang |first1=Yuehua |last2=Jiang |first2=Linzhe |last3=Zhou |first3=Fei |last4=Zhang |first4=Yi |last5=Fine |first5=Ryan D. |last6=Li |first6=Mingguang |title=The hidden dancers in water: the symbiotic mystery of Legionella pneumophila and free-living amoebae |journal=Frontiers in Microbiology |date=8 August 2025 |volume=16 |doi=10.3389/fmicb.2025.1634806 |doi-access=free|url=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1634806/full |language=English |issn=1664-302X|pmc=12370740 }}</ref>. Legionella bacteria are known to cause legionellosis<ref name="WHO2007">{{cite book |url=httpdss://apps.who.int/iris/bitstream/handle/10665/43233/9241562978_eng.pdf |title=Legionella and the prevention of legionellosis |date=2007 |publisher=World Health Organization |isbn=978-9241562973}}</ref> (all illnesses caused by ''Legionella'') including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever.<ref name="WHO2007" /> These bacteria are common in many places, like soil and water. ''Legionella'' are aerobic and motile.<ref>{{cite book |last1=Mahgoub |first1=Siham |last2=Awosika |first2=Ayoola O. |last3=Nguyen |first3=Andrew D. |last4=Tobin |first4=Ellis H. |title=Legionaires' Disease |date=February 17, 2026 |publisher=StatPearls Publishing |location=Treasure Island (FL) |url=https://www.ncbi.nlm.nih.gov/books/NBK430807/ |access-date=March 21, 2026}}</ref> There are over 50 species and 70 types (serogroups) identified. ''Legionella'' does not spread from person-to-person.<ref name=":0">{{Cite book |last=Winn |first=Washington C. |url=https://www.ncbi.nlm.nih.gov/books/NBK7627/ |title=Medical Microbiology |publisher=University of Texas Medical Branch at Galveston |year=1996 |isbn=0-9631172-1-1 |editor-last=Baron |editor-first=Samuel |edition=4th |chapter=Chapter 40: Legionella |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK7619/}}</ref> Most individuals who are exposed to the bacteria do not get sick.<ref>{{cite web |last=Kutty |first=Preeta K. |date=October 26, 2015 |title=What Everyone Needs to Know About Legionnaires Disease |url=https://www.medscape.com/viewarticle/852874 |work=Medscape}}</ref> Most outbreaks result from poorly maintained cooling towers.
The cell wall of the ''Legionella'' bacteria has parts that determine its specific type. The structural arrangement and building blocks (sugars) in the cell wall help classify the bacteria.
== Etymology == ''Legionella'' was named after a 1976 outbreak of a then-unknown "mystery disease" at a convention of the American Legion, an association of U.S. military veterans, in Philadelphia. This outbreak happened within days of the 200th anniversary of the signing of the Declaration of Independence, which led to it being highly publicized and caused great concern in the U.S.<ref name=":6">ISO 11731:2017 [https://www.iso.org/standard/32326.html Water quality – Detection and enumeration of Legionella – Part 2: Direct membrane filtration method for waters with low bacterial counts]</ref> On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named ''Legionella''.
== Detection == The detection of ''Legionella'' typically requires growing them on buffered charcoal yeast extract agar. As ''Legionella'' growth requires cysteine and iron, it cannot grow on other common lab media.
To detect ''Legionella'' in water, it is first concentrated, then inoculated into charcoal yeast extract agar containing selective agents that prevent the growth of other organisms.<ref name=":6" /> Heat or acid treatments are sometimes used to eliminate other microbes in a sample.<ref>{{Cite journal |last1=Rech |first1=Melanie M. |last2=Swalla |first2=Brian M. |last3=Dobranic |first3=Jason K. |date=2018-10-01 |title=Evaluation of Legiolert for Quantification of Legionella pneumophila from Non-potable Water |url=https://doi.org/10.1007/s00284-018-1522-0 |journal=Current Microbiology |language=en |volume=75 |issue=10 |pages=1282–1289 |doi=10.1007/s00284-018-1522-0 |issn=1432-0991 |pmc=6132855 |pmid=29980812}}</ref>
After incubation for up to ten days, the presence of ''Legionella'' can be confirmed if colonies grow on agar with cysteine but not on agar without it. Immunological techniques are then commonly used to determine the species and/or serogroups of bacteria present in the sample.<ref>{{Cite book |last=Baron |first=Samuel |title=Medical Microbiology |publisher=University of Texas Medical Branch |year=1996 |isbn=978-0963117212 |edition=4th |publication-date=January 1, 1996 |language=English}}</ref>alt=A black lateral flow test showing a negative result for Serogroup 1|left|thumb|An example of an LFICA test showing a negative result for Serogroup 1
Some hospitals use the ''Legionella'' urinary antigen test when ''Legionella'' pneumonia is suspected. This test is faster and uses a urine instead of a sputum sample, giving results in hours compared to days. However, it only detects one type of ''Legionella'': ''Legionella pneumophila serogroup 1'' (LP1).<ref>{{Cite journal |last1=Mercante |first1=Jeffrey W. |last2=Winchell |first2=Jonas M. |date=January 1, 2015 |title=Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations |journal=Clinical Microbiology Reviews |language=en |volume=28 |issue=1 |pages=95–133 |doi=10.1128/CMR.00029-14 |issn=0893-8512 |pmc=4284297 |pmid=25567224}}</ref> Non-LP1 strains can only be detected through culturing.
Methods like polymerase chain reaction (PCR) and rapid immunological tests can detect ''Legionella'' in water much faster.<ref>{{Cite web |last=CDC |date=2024-08-15 |title=Laboratory Testing for Legionella |url=https://www.cdc.gov/legionella/php/laboratories/?CDC_AAref_Val=https://www.cdc.gov/legionella/clinicians/diagnostic-testing.html |access-date=2024-11-01 |website=Legionella (Legionnaires' Disease and Pontiac Fever) |language=en-us}}</ref>
Government health surveillance reports have shown an increase in the proportion of water-related ''Legionella'' outbreaks, particularly in healthcare settings.<ref>{{cite journal |last1=Beer |first1=Karlyn D. |last2=Gargano |first2=Julia W. |last3=Roberts |first3=Virginia A. |last4=Hill |first4=Vincent R. |last5=Garrison |first5=Laurel E. |last6=Kutty |first6=Preeta K. |last7=Hilborn |first7=Elizabeth D. |last8=Wade |first8=Timothy J. |last9=Fullerton |first9=Kathleen E. |last10=Yoder |first10=Jonathan S. |date=August 14, 2015 |title=Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water – United States, 2011–2012 |journal=Morbidity and Mortality Weekly Report |volume=64 |issue=31 |pages=842–848 |doi=10.15585/mmwr.mm6431a2 |jstor=24856648 |pmc=4584589 |pmid=26270059}}</ref>
Genomic analyses of ''Legionella'' has resulted in the identification of 24 conserved signature indels (CSIs) in diverse proteins including 30S ribosomal protein S8, periplasmic serine endoprotease DegP precursor, DNA polymerase I, and ABC transporter permease, that are specifically present in different species of the ''Legionella''.<ref name=":5">{{Cite journal |last1=Saini |first1=Navneet |last2=Gupta |first2=Radhey S. |date=July 2021 |title=A robust phylogenetic framework for members of the order Legionellales and its main genera (Legionella, Aquicella, Coxiella and Rickettsiella) based on phylogenomic analyses and identification of molecular markers demarcating different clades |url=https://link.springer.com/10.1007/s10482-021-01569-9 |journal=Antonie van Leeuwenhoek |language=en |volume=114 |issue=7 |pages=957–982 |doi=10.1007/s10482-021-01569-9 |pmid=33881638 |issn=0003-6072|url-access=subscription }}</ref> These markers can help distinguish ''Legionella'' from other types of bacteria, improving diagnosis.<ref name=":5" />
=== Sources === Documented sources include cooling towers,<ref>{{cite journal |vauthors=Osawa K, Shigemura K, Abe Y, etal |title=A case of nosocomial Legionella pneumonia associated with a contaminated hospital cooling tower |journal=Journal of Infection and Chemotherapy |volume=20 |issue=1 |pages=68–70 |date=January 2014 |pmid=24462430 |doi=10.1016/j.jiac.2013.07.007}}</ref> swimming pools, domestic water systems, showers, ice-making machines,<ref>{{cite journal |vauthors=Graman PS, Quinlan GA, Rank JA |title=Nosocomial legionellosis traced to a contaminated ice machine |journal=Infection Control and Hospital Epidemiology |volume=18 |issue=9 |pages=637–40 |date=September 1997 |pmid=9309436 |doi=10.2307/30141491 |jstor=30141491|s2cid=32896608 }}</ref> refrigerated cabinets, whirlpool spas,<ref>{{cite journal |vauthors=Coetzee N, Duggal H, Hawker J, etal |title=An outbreak of Legionnaires' disease associated with a display spa pool in retail premises, Stoke-on-Trent, United Kingdom, July 2012 |journal=Euro Surveillance |volume=17 |issue=37 |year=2012 |doi=10.2807/ese.17.37.20271-en |pmid=22995431 |doi-access=free }}</ref><ref>{{cite journal |vauthors=Campese C, Roche D, Clément C, etal |title=Cluster of Legionnaires' disease associated with a public whirlpool spa, France, April-May 2010 |journal=Euro Surveillance |volume=15 |issue=26 |date=July 2010 |doi=10.2807/ese.15.26.19602-en |pmid=20619131 |doi-access=free }}</ref> hot springs,<ref>{{cite journal |vauthors=Kurosawa H, Fujita M, Kobatake S, etal |title=A case of Legionella pneumonia linked to a hot spring facility in Gunma Prefecture, Japan |journal=Japanese Journal of Infectious Diseases |volume=63 |issue=1 |pages=78–9 |date=January 2010 |doi=10.7883/yoken.63.78 |pmid=20093771 |s2cid=43919158 |url=http://www0.nih.go.jp/JJID/63/78.html|doi-access=free }}</ref> fountains,<ref>{{cite journal |vauthors=Palmore TN, Stock F, White M, etal |title=A cluster of cases of nosocomial legionnaires disease linked to a contaminated hospital decorative water fountain |journal=Infection Control and Hospital Epidemiology |volume=30 |issue=8 |pages=764–8 |date=August 2009 |pmid=19580436 |pmc=2886954 |doi=10.1086/598855}}</ref> dental equipment,<ref>{{cite journal |vauthors=Kadaifciler DG, Cotuk A |title=Microbial contamination of dental unit waterlines and effect on quality of indoor air |journal=Environmental Monitoring and Assessment |volume=186 |issue=6 |pages=3431–44 |date=June 2014 |pmid=24469014 |doi=10.1007/s10661-014-3628-6 |bibcode=2014EMnAs.186.3431K |s2cid=207135938}}</ref> soil,<ref>Infection Due to Legionella Species Other Than L. pneumophila Barry S. Fields*, Robert F. Benson, and Richard E. Besser https://academic.oup.com/cid/article/35/8/990/330989</ref> automobile windshield washer fluid (especially if filled with water instead of wiper fluid),<ref>{{citation |author=American Society for Microbiology |title=Windshield washer fluid a source of Legionnaires: Found in most school buses |url=https://www.sciencedaily.com/releases/2014/05/140518164421.htm}}</ref> industrial coolant<ref>RR910 - Survival of Legionella pneumophila in metalworking fluids https://www.hse.gov.uk/research/rrhtm/rr910.htm</ref> and waste water treatment plants.{{fact|date=January 2025}}
Air-conditioning units that do not use water to cool air cannot be sources of infection.<ref name=":1">{{cite web |date=November 3, 2024 |title=Legionella - Causes and Transmission - Legionnaires |url=https://www.cdc.gov/legionella/causes/?CDC_AAref_Val=https://www.cdc.gov/legionella/about/causes-transmission.html |website=CDC}}</ref>
==== Airborne transmission ==== The bacteria can spread through tiny droplets of water that get into the air. People can breathe in these droplets, which then infect cells in the airways, resulting in illness. This is the most common way Legionella spreads.<ref name=":1" />
==== Recreational exposure ==== Cooling towers are well established as sources of ''Legionella'' that may have an effect on community exposure to the bacterium and Legionnaires' disease epidemics.<ref>{{cite journal |last1=García-Fulgueiras |first1=Ana |last2=Navarro |first2=Carmen |last3=Fenoll |first3=Daniel |last4=García |first4=José |last5=González-Diego |first5=Paulino |last6=Jiménez-Buñuales |first6=Teresa |last7=Rodriguez |first7=Miguel |last8=Lopez |first8=Rosa |last9=Pacheco |first9=Francisco |last10=Ruiz |first10=Joaquín |last11=Segovia |first11=Manuel |date=August 2003 |title=Legionnaires' Disease Outbreak in Murcia, Spain |url=http://wwwnc.cdc.gov/eid/article/9/8/03-0337_article.htm |journal=Emerging Infectious Diseases |volume=9 |issue=8 |pages=915–921 |doi=10.3201/eid0908.030337 |pmc=3020623 |pmid=12967487}}</ref> In addition to cooling towers, use of swimming pools, spa pools, and other recreational water bodies has also been shown to increase risk of exposure to ''Legionella'', though this differs by species of ''Legionella''.<ref name=":7" /> In a review of disease caused by recreational exposure to ''Legionella'', most exposures occurred in spas or pools used by the public (hotels or recreational centers) or in natural settings (hot springs or thermal water).<ref name=":7" />
Hotels and other tourist destinations have contributed to ''Legionella'' exposure.<ref name=":2">{{cite journal |last1=De Giglio |first1=Osvalda |last2=Napoli |first2=Christian |last3=Diella |first3=Giusy |last4=Fasano |first4=Fabrizio |last5=Lopuzzo |first5=Marco |last6=Apollonio |first6=Francesca |last7=D'Ambrosio |first7=Marilena |last8=Campanale |first8=Carmen |last9=Triggiano |first9=Francesco |last10=Caggiano |first10=Giuseppina |last11=Montagna |first11=Maria Teresa |date=November 2021 |title=Integrated approach for legionellosis risk analysis in touristic-recreational facilities |journal=Environmental Research |language=en |volume=202 |article-number=111649 |doi=10.1016/j.envres.2021.111649 |pmid=34252427 |bibcode=2021ER....20211649D |doi-access=free |hdl=11573/1561995 |hdl-access=free }}</ref> The relative danger at commonly used facilities with heating and cooling water systems depends on several factors, such as the water source, how much ''Legionella'' is present (if there is any), if and how the water system is treated, how people are interacting with this water, and other factors that make the water systems so dynamic.<ref name=":2" />
In addition to tourists and other recreators, gardeners may be at increased risk for exposure to ''Legionella''.<ref name=":3">{{cite journal |last=Walker |first=Jt |date=September 2018 |title=The influence of climate change on waterborne disease and Legionella: a review |url=http://journals.sagepub.com/doi/10.1177/1757913918791198 |journal=Perspectives in Public Health |language=en |volume=138 |issue=5 |pages=282–286 |doi=10.1177/1757913918791198 |pmid=30156484 |s2cid=52115812 |url-access=subscription }}</ref> In some countries (like Australia), ''Legionella'' lives in soil and compost.<ref name=":3" /> Warmer temperatures and increased rainfall in some regions of the world due to climate change may impact ''Legionella'' in soil, gardeners' seasonal exposure to contaminated soil, and complex water systems used by the public.<ref name=":3" />
==== Exposure related to natural disasters and climate change ==== Not only are ''Legionella'' spp. present in artificial water systems and infrastructure, but also these bacteria live in natural bodies of water, such as lakes and rivers.<ref>{{Cite journal |last1=Passer |first1=J. K. |last2=Danila |first2=R. N. |last3=Laine |first3=E. S. |last4=Como-Sabetti |first4=K. J. |last5=Tang |first5=W. |last6=Searle |first6=K. M. |date=2020-06-29 |title=The association between sporadic Legionnaires' disease and weather and environmental factors, Minnesota, 2011-2018 |journal=Epidemiology and Infection |volume=148 |article-number=e156 |doi=10.1017/S0950268820001417 |issn=1469-4409 |pmc=7378963 |pmid=32594925}}</ref> Weather patterns and other environmental factors may increase 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 risk of ''Legionella'' exposure when taking into account other environmental factors (temperature, relative humidity, land use and age of infected person).<ref name=":7">{{cite journal |last1=Passer |first1=J. K. |last2=Danila |first2=R. N. |last3=Laine |first3=E. S. |last4=Como-Sabetti |first4=K. J. |last5=Tang |first5=W. |last6=Searle |first6=K. M. |date=2020 |title=The association between sporadic Legionnaires' disease and weather and environmental factors, Minnesota, 2011–2018 |journal=Epidemiology and Infection |language=en |volume=148 |article-number=e156 |doi=10.1017/S0950268820001417 |pmc=7378963 |pmid=32594925}}</ref> 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.<ref name=":3" /> Severe rain patterns can increase risk of water source contamination through flooding and unseasonable rains; therefore, natural disasters, especially those associated with climate change, may increase risk of exposure to ''Legionella''.<ref name=":3" />
=== Vaccine research === No vaccine is available for legionellosis.<ref>{{Cite web |date=2022-09-06 |title=Legionellosis |url=https://www.who.int/news-room/fact-sheets/detail/legionellosis |access-date=2023-12-04 |website=WHO |language=en}}</ref><ref>{{Cite journal |last1=Khan |first1=Md Tahsin |last2=Mahmud |first2=Araf |last3=Hasan |first3=Mahmudul |last4=Azim |first4=Kazi Faizul |last5=Begum |first5=Musammat Kulsuma |last6=Rolin |first6=Mohimenul Haque |last7=Akter |first7=Arzuba |last8=Mondal |first8=Shakhinur Islam |date=2022-08-31 |editor-last=Faucher |editor-first=Sébastien P. |title=Proteome Exploration of Legionella pneumophila To Identify Novel Therapeutics: a Hierarchical Subtractive Genomics and Reverse Vaccinology Approach |journal=Microbiology Spectrum |language=en |volume=10 |issue=4 |pages=e0037322 |doi=10.1128/spectrum.00373-22 |doi-access=free|issn=2165-0497 |pmc=9430848 |pmid=35863001}}</ref> Vaccination studies using heat-killed or acetone-killed cells have been carried out in guinea pigs, which were then given ''Legionella'' intraperitoneally or by aerosol. Both vaccines were shown to give moderately high levels of protection. Protection was dose-dependent and correlated with antibody levels as measured by enzyme-linked immunosorbent assay (ELISA) to an outer membrane antigen and by indirect immunofluorescence to heat-killed cells.<ref>{{Cite journal |last1=Eisenstein |first1=T. K. |last2=Tamada |first2=R. |last3=Meissler |first3=J. |last4=Flesher |first4=A. |last5=Oels |first5=H. C. |date=1984 |title=Vaccination against Legionella pneumophila: serum antibody correlates with protection induced by heat-killed or acetone-killed cells against intraperitoneal but not aerosol infection in guinea pigs |journal=Infection and Immunity |volume=45 |issue=3 |pages=685–691 |doi=10.1128/iai.45.3.685-691.1984 |issn=0019-9567 |pmid=6469355|pmc=263350 }}</ref>
== Molecular biology == ''Legionella'' is a genetically diverse species with 32% of genes being strain-specific<ref>{{cite journal |title=PNAS |journal=PNAS |doi=10.1073/pnas.1808016116 |url=https://www.pnas.org/doi/10.1073/pnas.1808016116 |language=en}}</ref>. The molecular function of some of the proven virulence factors of ''Legionella'' have been discovered.<ref>{{cite journal |vauthors=Raychaudhury S, Farelli JD, Montminy TP |display-authors=etal |title=Structure and function of interacting IcmR-IcmQ domains from a type IVb secretion system in Legionella pneumophila |journal=Structure |volume=17 |issue=4 |pages=590–601 |date=April 2009 |pmid=19368892 |doi=10.1016/j.str.2009.02.011 |pmc=2693034}}</ref>
== ''Legionella'' disease manifestation == === Signs and symptoms === Legionella pneumonia, often called ''atypical pneumonia'', is the most common form of legionellosis. The early symptoms are general, including fever, muscle pain, headache, shortness of breath, and a dry or productive cough. Patients with pneumonia who also have neurological or gastrointestinal symptoms like loss of appetite, nausea, or vomiting may be more likely to have legionellosis. A physical examination may reveal abnormal lungs sounds such as rales or rhonchi, and if consolidation is present, there may be signs like egophony or dullness to percussion. Laboratory tests might show either a high or low white blood cell count, low platelets, elevated liver enzymes (ALT, AST), low sodium levels, and possibly decreased kidney function.<ref name=":8">{{Cite book |title=Harrison's Principles of Internal Medicine |date=2022 |publisher=McGraw Hill |isbn=978-1-264-26851-1 |editor-last=Loscalzo |editor-first=Joseph |edition=21st |location=New York |publication-date=March 28, 2022 |editor-last2=Fauci |editor-first2=Anthony S. |editor-last3=Kasper |editor-first3=Dennis L. |editor-last4=Hauser |editor-first4=Stephen L. |editor-last5=Longo |editor-first5=Dan L. |editor-last6=Jameson |editor-first6=J. Larry}}</ref>
Another form of legionellosis is Pontiac fever, which resembles the flu and includes symptoms like fever, headache, muscle pain, chills, dizziness, nausea, vomiting, and diarrhea. This form is milder than Legionella pneumonia and typically resolves on its own.<ref name=":8" />
In some cases, ''Legionella'' can cause infections outside the lungs, including skin and soft tissue infections similar to cellulitis. This is especially a concern if contaminated water comes into contact with surgical wounds. It can also lead to heart infections, such as prosthetic valve endocarditis (without positive blood cultures), myocarditis, and pericarditis. In rare cases, ''Legionella'' species have been linked to joint infections (example: septic arthritis) and sinusitis.<ref name=":8" />
=== Pathogenesis === thumb|upright|left|A ''Legionella pneumophila ''bacterium (green) caught by a ''Vermamoeba vermiformis'' amoeba (orange) In nature, ''Legionella'' bacteria live inside tiny organisms, like amoebae (examples: ''Acanthamoeba'' spp., ''Naegleria'' spp., ''Vermamoeba'' spp., or other protozoa such as ''Tetrahymena pyriformis''<ref name="Swanson_2000">{{cite journal |vauthors=Swanson MS, Hammer BK |year=2000 |title=Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages |journal=Annual Review of Microbiology |volume=54 |pages=567–613 |doi=10.1146/annurev.micro.54.1.567 |pmid=11018138 |s2cid=19944003}}</ref>). These amoebae are found in water and soil. They are found in low amounts in natural water sources like lakes and streams, but can grow quickly in man-made water systems under the right conditions.<ref>{{Cite journal |last1=Oliva |first1=Giulia |last2=Sahr |first2=Tobias |last3=Buchrieser |first3=Carmen |date=2018-01-19 |title=The Life Cycle of L. pneumophila: Cellular Differentiation Is Linked to Virulence and Metabolism |journal=Frontiers in Cellular and Infection Microbiology |volume=8 |article-number=3 |doi=10.3389/fcimb.2018.00003 |issn=2235-2988 |pmc=5780407 |pmid=29404281 |doi-access=free}}</ref>
''Legionella'' is spread through inhaling contaminated water droplets, which can come from mists, sprays, or other sources that release tiny droplets into the air.<ref name=":1" /> In homes, the most common sources of exposure are shower heads and sinks. The incubation period, or the time it takes for symptoms to appear, is usually two to ten days for Legionella pneumonia and one to three days for Pontiac fever.<ref name=":8" /> In rare cases, infection can also happen if people accidentally breathe in drinking water. Person-to-person spread has not been proven,<ref name=":0" /> but could be possible in rare situations.<ref name=":1" />
Most healthy people don't get severely sick. The risk of ''Legionella'' infection is higher in adults, especially those over 40 years old. People with certain health conditions, like kidney or liver disease, chronic lung disease, or heart disease, are at a greater risk. Those with weakened immune systems, such as cancer patients or organ transplant recipients, are at risk as well. People with chronic illnesses, like autoimmune disease treated with TNF inhibitors, also face a higher risk of infection. Men are about three times more likely than women to get infected, while children are less likely to develop severe cases. Smoking, including cannabis smoking, is strongly linked to increased risk due to damage to the airway lining.<ref name=":8" />
Hospitals and nursing homes are especially concerned about water system safety because vulnerable patients are at a higher risk. For example, the Texas Department of State Health Services, has guidelines for hospitals to stop the spread of ''Legionella''.<ref>{{Cite web |title=Legionellosis (Legionnaires' Disease) Task Force Recommendations |url=https://www.dshs.texas.gov/legionellosis-legionnaires-disease/legionellosis-legionnaires-disease-task-force-recommendations |access-date=2023-12-04 |website=Texas DSHS}}</ref>
In the United States, ''Legionella'' infects about 8,000 to 18,000 people each year.<ref>{{cite web |date= 11 January 2023|title=Legionella (Legionnaires' Disease and Pontiac Fever) |url=https://www.cdc.gov/legionella/fastfacts.html |access-date=November 3, 2024 |website=CDC}}</ref> Preventing exposure to contaminated water droplets remains key to reducing spread.
=== Mechanism === After inhaling or accidentally swallowing small aerosol particles, ''Legionella'' bacteria attach to immune cells and are taken up by them through a process called phagocytosis. Inside the body, the bacteria can grow and multiply in lung cells, specifically alveolar macrophages and monocytes.<ref name=":8" />
''Legionella'' has several ways to evade the immune system, increasing the chance that a person develops symptoms of infection. It creates special vacuoles, or protective bubbles, inside immune cells to hide from the body's defenses. It also reduces the activity of cytokine receptors (which play a role in immune response), blocks the production of certain proteins needed by the host, and avoids being broken down by lysosomes, which are cell structures meant to digest harmful particles.<ref name=":8" />
=== Diagnosis === ''Legionella'' is usually diagnosed using a urinary antigen test. Some patients, especially those in the ICU or those who cannot provide a sputum sample, may need an invasive procedure, such as a bronchoscopy, if the initial urinary antigen test is negative. For the most accurate diagnosis, doctors may take cultures from sputum, fluid from the lungs (called bronchoalveolar lavage), lung tissue, or other affected areas. These cultures are considered the "gold standard" for confirming ''Legionella'' infection.<ref name=":8" />
=== Prevention and screening === Preventing ''Legionella'' infection starts with improving water systems and setting up water-monitoring processes to keep it under control.<ref name=":1" /> In the U.S., prevention efforts focus mainly on health care settings, especially hospitals, where water-based exposures are more likely to be fatal. Federal guidelines to reduce ''Legionella'' risks were first introduced in June 2017, requiring all medical centers to monitor water quality and have systems in place to prevent hospital-acquired Legionella pneumonia. Facilities with water features, like therapy pools, ice machines, and decorative fountains, must have cleaning and disinfection policies.<ref name=":8" />
To remove ''Legionella'' from water systems, chemical disinfectants are often added. Water filtration can also be used, either at the plumbing level or at specific points of use, as a primary or combined prevention method. Using disinfectants requires regular maintenance and monitoring of chemical levels to ensure they're effective in preventing ''Legionella'' growth.<ref name=":8" />
=== Treatment === Antibiotics are usually the first choice when treating community-acquired pneumonia, which may or may not be caused by ''Legionella''. The first-line options when ''Legionella'' is the causative agent are macrolides and fluoroquinolones. Azithromycin, a type of macrolide, is the preferred choice. For patients with mild illness, the treatment course usually lasts about 10–14 days, although most symptoms tend to improve within five days of starting the antibiotics. For patients who are immunosuppressed or have severe cases of ''Legionella'' pneumonia, a longer treatment course of three weeks is recommended to ensure effective recovery.<ref name=":8" />
=== Outcomes and prognosis === Even with the right treatment, ''Legionella'' pneumonia can lead to serious health problems and can be life-threatening. The case fatality rate for this type of pneumonia is about 10%, and patients who are admitted to the ICU or have other major health issues are more likely to die from it.<ref name=":8" /> If there is a delay in starting antibiotic treatment, the risk of death can be about three times higher compared to those who receive treatment promptly.<ref name=":8" /> Among patients who develop pneumonia in the hospital, especially cases caused by ''Legionella'', the death rate is around 25%. For those who are immunocompromised, the mortality rate can be as high as 30–50%.<ref name=":8" />
After surviving ''Legionella'' pneumonia, many patients experience long-term complications, with more than 25% facing ongoing issues such as recurrent hospitalizations, acute kidney failure, lung problems, and recurring pneumonia.<ref name=":8" /> On the other hand, recovery from Pontiac fever usually occurs within five days, and serious complications or death related to Pontiac fever are very rare.<ref name=":8" />
=== Epidemiology === ''Legionella'' is responsible for more than 50% of all waterborne outbreaks and over 10% of diseases related to drinking water in the U.S. The incidence of legionellosis, or Legionella infection, is about two to three cases annually per {{val|100000}} people; however, the true number of cases is likely higher than reported.<ref name=":8" /> This is because many studies on community-acquired pneumonia do not routinely test for ''Legionella'', meaning some cases may go undetected.<ref name=":8" />
=== History === Examples of common-source outbreaks:<ref name=":8" />
* 2001 Spain; source: cooling tower; 449 documented cases of Legionnaires' disease<ref name="pmid12967487">{{cite journal |vauthors=García-Fulgueiras A, Navarro C, Fenoll D, García J, González-Diego P, Jiménez-Buñuales T, Rodriguez M, Lopez R, Pacheco F, Ruiz J, Segovia M, Balandrón B, Pelaz C |title=Legionnaires' disease outbreak in Murcia, Spain |journal=Emerging Infectious Diseases |volume=9 |issue=8 |pages=915–21 |date=August 2003 |pmid=12967487 |pmc=3020623 |doi=10.3201/eid0908.030337 |url=}}</ref> * 2012: Hotel; source: potable water, fountain, spa; # cases: 89 (+29 suspected) * 2012: Hospital; source: potable water; # cases: 22 * 2014: Community; source: cooling tower; # cases: 334 * 2014-2015: Hospital/community; source: potable water, household, cooling towers; # case: 86 * 2015: Long-term care facility; source: potable water; # cases: 74 * 2018: Hospital; source: potable water, showers; # cases: 128 * 2019: Hotel; source: fountain; # cases: 13 (+66 suspected) * 2019: Community; source: hot tub display; # cases: 141
== ''Legionella'' control and biomonitoring == Control of ''Legionella'' growth can occur through chemical, thermal or ultraviolet treatment methods.<ref>{{Cite book |author=((National Academies of Sciences, Engineering, and Medicine)) |title=Management of ''Legionella'' in Water Systems. |publisher=National Academies Press |year=2019 |isbn=978-0-309-49947-7 |location=Washington DC, US |chapter=Strategies for ''Legionella'' Control and Their Application in Building Water Systems |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK555108/}}</ref>
=== Heat === One option is temperature control{{dash}}i.e., keeping all cold water below {{convert|20|C|F}} and all hot water above {{convert|51|C|F}}.<ref name="WHO2007" />
Temperature affects the survival of ''Legionella'' as follows:<ref name="WHO2007"/> * Above {{convert|70|°C|°F|abbr=on}} – ''Legionella'' dies almost instantly * At {{convert|60|°C|°F|abbr=on}} – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes) * At {{convert|50|°C|°F|abbr=on}} – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes) * {{convert|48|to|50|C|F}} – can survive but do not multiply * {{convert|32|to|42|C|F}} – ideal growth range * {{convert|25|to|45|C|F}} – growth range * Below {{convert|20|°C|°F|abbr=on}} – can survive, but are dormant
Other temperature sensitivity:<ref>{{cite web |title=Safe Hot Water Temperature |url=http://www.ciphe.org.uk/Global/Databyte/Safe%20Hot%20Water.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110626201630/http://www.ciphe.org.uk/Global/Databyte/Safe%20Hot%20Water.pdf |archive-date=2011-06-26 |website=Chartered Institute of Plumbing and Heating Engineering}}</ref><ref>{{cite web |title=Employers Guide to the control of ''Legionella'' |url=http://www.hse.gov.uk/pubns/iacl27.pdf |url-status=dead |archive-url=https://web.archive.org/web/20080611231131/http://www.hse.gov.uk/pubns/iacl27.pdf |archive-date=11 June 2008 |access-date=14 July 2019 |website=Health and Safety Executive}}</ref> * {{convert|60|to|70|°C|°F|abbr=on}} to {{convert|80|°C|°F|abbr=on}} – Disinfection range * {{convert|66|°C|°F|abbr=on}} – ''Legionella'' dies within 2 minutes * {{convert|60|°C|°F|abbr=on}} – ''Legionella'' dies within 32 minutes * {{convert|55|°C|°F|abbr=on}} – ''Legionella'' dies within 5 to 6 hours
Water temperature can be monitored in real time with electronic devices.<ref>{{Cite journal |last1=Whiley |first1=Harriet |last2=Hinds |first2=Jason |last3=Xi |first3=James |last4=Bentham |first4=Richard |date=2019 |title=Real-Time Continuous Surveillance of Temperature and Flow Events Presents a Novel Monitoring Approach for Hospital and Healthcare Water Distribution Systems |journal=International Journal of Environmental Research and Public Health |volume=16 |issue=8 |pages=1332 |doi=10.3390/ijerph16081332 |doi-access=free |issn=1661-7827 |pmc=6518245 |pmid=31013887}}</ref>
=== Controlling ''Legionella'' in potable water systems === Potable water is water that is intended for drinking. The CDC recommends that hot water is kept between {{convert|60|°C|°F}} and {{convert|49|°C|°F}} and that cold water is stored below {{convert|20|°C|°F}}. It is also recommended to flush infrequently used fixtures regularly.<ref>{{Cite web |last=CDC |date=2024-04-02 |title=Controlling Legionella in Potable Water Systems |url=https://www.cdc.gov/control-legionella/php/toolkit/potable-water-systems-module.html#:~:text=Recommendations:%20Store%20hot%20water%20above,F%20(20%C2%B0C). |access-date=2024-10-24 |website=Controlling Legionella |language=en-us}}</ref>
=== In building water systems === ==== Chlorine ==== A very effective chemical treatment is chlorine. For systems with marginal issues, chlorine provides effective results at >0.5 ppm<ref>{{cite web |date=2013 |title=HSG274 Part 1 Legionnaires' disease: Technical guidance |url=https://legionellacontrol.com/wp-content/uploads/2013/11/HSG274-Part-1-Evaporative-Cooling-Compliments-Legionella-Control-International.pdf |access-date=2023-02-06 |website=legionellacontrol.com |publisher=Health and Safety Executive - UK}}</ref> residual in the hot water system. For systems with significant ''Legionella'' problems, temporary shock chlorination{{dash}}where levels are raised to higher than 2 ppm for a period of 24 hours or more and then returned to 0.5 ppm{{dash}}may be effective.<ref>{{Cite web |date=2003 |title=Guidelines for Environmental Infection Control in Health-Care Facilities |url=https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/water.html |access-date=2023-12-04 |website=CDC |language=en-us}}</ref> 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.<ref>{{cite web |last1=Reiff |first1=Fred |title=Legionella Control in Institutional Water Systems |url=http://www.waterandhealth.org/legionella-control-in-institutional-water-systems/ |website=Water Quality and Health Council |access-date=18 January 2017 |date=22 January 2010}}</ref>
==== Copper–silver ionization ==== Copper–silver ionization is recognized by the U.S. Environmental Protection Agency and WHO for ''Legionella'' control and prevention.<ref>{{Cite book |last1=Fewtrell |first1=Lorna |url=https://cdn.who.int/media/docs/default-source/wash-documents/wash-chemicals/silver-020320188b233a75-5b6f-489d-bff5-99d7f2e77d98.pdf?sfvrsn=fed05531_3 |title=Silver as a drinking-water disinfectant |last2=Bevan |first2=Ruth |date=2018 |publisher=World Health Organization |isbn=978-92-4-151369-2 |access-date=2023-12-04}}</ref><ref>{{Cite web |author=((Office of Water)) |date=2001 |title=Legionella: Drinking Water Health Advisory |url=https://www.epa.gov/sites/default/files/2015-10/documents/legionella-report.pdf |access-date=2023-12-04 |publisher=US Environmental Protection Agency |id=EPA-822-B-01-005}}</ref> It is a popular method used in building water systems to control ''Legionella'' bacteria, mainly because it is affordable and does not require much maintenance. In this method, the copper ions weaken the bacteria's cell wall, allowing silver ions to then disrupt the bacteria's DNA and proteins, preventing further proliferation.<ref name=":02">{{Citation |last1=National Academies of Sciences |first1=Engineering |title=Strategies for Legionella Control and Their Application in Building Water Systems |date=2019-08-14 |work=Management of Legionella in Water Systems |url=https://www.ncbi.nlm.nih.gov/books/NBK555108/ |access-date=2024-10-24 |publisher=National Academies Press (US) |language=en |last2=Division |first2=Health and Medicine |last3=Studies |first3=Division on Earth and Life |last4=Practice |first4=Board on Population Health and Public Health |last5=Sciences |first5=Board on Life |last6=Board |first6=Water Science and Technology |last7=Systems |first7=Committee on Management of Legionella in Water}}</ref> Copper and silver ion concentrations must be maintained at optimal levels, taking into account both water flow and overall water usage, to control ''Legionella''.
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, that cause ionic copper to precipitate. Furthermore, tolyltriazole, 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.<ref name="iche2">{{cite journal |last1=Stout |first1=Janet E. |last2=Yu |first2=Victor L. |date=August 2003 |title=Experiences of the First 16 Hospitals Using Copper–Silver Ionization for Legionella Control: Implications for the Evaluation of Other Disinfection Modalities |journal=Infection Control & Hospital Epidemiology |volume=24 |issue=8 |pages=563–568 |doi=10.1086/502251 |pmid=12940575 |quote=(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.}}</ref> Copper–silver ionization works slower than other disinfectants and is affected by the water's chemical makeup.<ref name=":02" />
==== 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 some other chlorine sources when used in the purification of drinking water that contains natural organic compounds such as humic and fulvic acids; trihalomethanes may be formed. Drinking water containing such molecules has been shown to increase the risk of cancer.
Since chlorine dioxide stays as a gas, it is easier for it to enter microorganisms to disrupt their internal functions. It works better than chlorine when it comes to disrupting biofilms and is effective across a wider pH range. Testing has demonstrated that low levels of chlorine dioxide reduced Legionella bacteria to undetectable levels in six days; however, its effectiveness can be reduced when amoebae are present.<ref name=":03">{{Citation |last1=National Academies of Sciences |first1=Engineering |title=Strategies for Legionella Control and Their Application in Building Water Systems |date=2019-08-14 |work=Management of Legionella in Water Systems |url=https://www.ncbi.nlm.nih.gov/books/NBK555108/ |access-date=2024-10-24 |publisher=National Academies Press (US) |language=en |last2=Division |first2=Health and Medicine |last3=Studies |first3=Division on Earth and Life |last4=Practice |first4=Board on Population Health and Public Health |last5=Sciences |first5=Board on Life |last6=Board |first6=Water Science and Technology |last7=Systems |first7=Committee on Management of Legionella in Water}}</ref> It is also not widely distributed in water systems due to concerns regarding its toxicity, unpleasant odors, and harmful byproducts, as stated above, that it can create.
Monochloramine is an alternative. It is created by mixing chlorine and ammonia and valued for its stability and ability to penetrate biofilms better than chlorine. Like chlorine and chlorine dioxide, monochloramine is approved by the U.S. Environmental Protection Agency as a primary potable water disinfectant. Environmental Protection Agency registration requires a biocide label, which lists toxicity and other data required for all registered biocides.
It does work slower than chlorine and requires precise chemical management due to concerns for toxicity.<ref name=":03" />
==== Ultraviolet light ==== Ultraviolet light, in the range of 200 to 300 nm, can inactivate Legionella. According to a review by the US EPA, three-log (99.9%) inactivation can be achieved with a dose of less than 7 mJ/cm<sup>2</sup>.<ref name=":4">{{Cite web |date=2016 |title=Technologies for ''Legionella'' Control in Premise Plumbing Systems: Scientific Literature Review |url=https://www.epa.gov/sites/default/files/2016-09/documents/legionella_document_master_september_2016_final.pdf |website=EPA |page=60}}</ref>
==== Biomonitoring ==== A ''Legionella''-specific aptamer has been discovered<ref>{{cite journal |last1=Saad |first1=Mariam |last2=Chinerman |first2=Deanna |last3=Tabrizian |first3=Maryam |last4=Faucher |first4=Sebastien |title=Identification of two aptamers binding to Legionella pneumophila with high affinity and specificity |journal=Scientific Reports |date=2020 |volume=10 |issue=1 |page=9145 |doi=10.1038/s41598-020-65973-3 |pmid=32499557 |pmc=7272621 |bibcode=2020NatSR..10.9145S }}</ref> and in 2022 was developed into an assay for detecting to a limit of 10<sup>4.3</sup> cells/mL with no processing steps.<ref>{{cite journal |last1=Saad |first1=Mariam |last2=Castiello |first2=F. Rafael |last3=Sebastien |first3=Faucher |last4=Tabrizian |first4=Maryam |title=Introducing an SPRi-based titration assay using aptamers for the detection of Legionella pneumophila |journal=Sensors and Actuators B: Chemical |date=15 January 2022 |volume=351 |article-number=130933 |doi=10.1016/j.snb.2021.130933 |bibcode=2022SeAcB.35130933S |s2cid=244584437 |url=https://www.sciencedirect.com/science/article/pii/S092540052101501X |access-date=2 July 2022|url-access=subscription }}</ref>
== European standards == Several European countries established the European Working Group for Legionella Infections<ref>{{cite web |url=http://www.ewgli.org |title=European Working Group for ''Legionella'' Infections |access-date=2006-07-07 |archive-url=https://web.archive.org/web/20121225121713/http://www.ewgli.org/ |archive-date=2012-12-25 |url-status=dead}}</ref> 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 are able to multiply) of ''Legionella'' per litre:
{| class="wikitable" |- !width=22%|''Legionella'' bacteria CFU/litre!!Action required (35 samples per facility are required, including 20 water and 10 swabs) |- | align=center|1000 or less || System under control |- | align=center|more than 1000<br />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. |- | align=center|more than 10,000 || 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.) |}
Monitoring guidelines are stated in Approved Code of Practice L8 in the UK. These are not mandatory, but are widely regarded as so. An employer or property owner must follow an Approved Code of Practice, 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 – neither could prove a sufficient scheme to be in place while investigating an outbreak, therefore both were fined about £300,000GBP. Important case law in this area is R v Trustees of the Science Museum 3 All ER 853, (1993) 1 WLR 1171.<ref>{{cite web |last1=Whittaker |first1=Howard |title=The Law & Legionella (& HSE's Enforcement strategy) |url=http://www.hse.gov.uk/chemicals/workshop/legionella-09/law-and-legionella.pdf}}</ref>
Employers and those responsible for premises within the UK are required under Control of Substances Hazardous to Health to undertake an assessment of the risks arising from Legionella. This risk assessment may be very simple for low risk premises, however for larger or higher risk properties may include a narrative of the site, asset register, simplified schematic drawings, recommendations on compliance, and a proposed monitoring scheme.<ref>{{Cite web |title=Legionnaires' disease - What you must do |url=https://www.hse.gov.uk/legionnaires/what-you-must-do.htm |accessdate=2023-05-17 |website=Health and Safety Executive}}</ref>
The L8 Approved Code of Practice recommends that the risk assessment should be reviewed at least every 2 years and whenever a reason exists to suspect it is no longer valid, such as water systems have been amended or modified, or if the use of the water system has changed, or if there is reason to suspect that Legionella control measures are no longer working.<ref>{{Cite book |title=Approved Code of Practice L8: Legionnaires' Disease |publisher=Health & Safety Executive |year=2013 |isbn=9780717666157 |edition=4th |location=London, UK |publication-date=2013 |language=English}}</ref>
== Weaponization == ''Legionella'' can be used as a weapon, and indeed genetic modification of ''L. pneumophila'' has been shown where the mortality rate in infected animals can be increased to nearly 100%.<ref>{{cite web |last1=Bhargava |first1=Pushpa M. |title=The Growing Planetary Threat From Biological Weapons and Terrorism |url=http://www.aina.org/news/20081201063837.htm |website=aina.org |publisher=Assyrian International News Agency |date=December 1, 2008 |access-date=June 16, 2017}}</ref><ref>{{cite journal |vauthors=Gilsdorf JR, Zilinskas RA |title=New considerations in infectious disease outbreaks: the threat of genetically modified microbes |journal=Clinical Infectious Diseases |volume=40 |issue=8 |pages=1160–5 |date=April 2005 |pmid=15791517 |doi=10.1086/428843 |jstor=4463254 |doi-access=free}}</ref><ref name=homeland>{{cite web |title=Interview – Serguei Popov |archive-url=https://web.archive.org/web/20110927023507/http://www.homelandsecurity.org/journal/Interviews/PopovInterview_001107.htm |url=http://www.homelandsecurity.org/journal/Interviews/PopovInterview_001107.htm |archive-date=September 27, 2011 |date=November 1, 2000 |access-date=June 16, 2017 |url-status=dead}}</ref> A former Soviet bioengineer, Sergei Popov, stated in 2000 that his team experimented with genetically enhanced bioweapons, including ''Legionella''.<ref name=homeland/> Popov worked as a lead researcher at the Vector Institute from 1976 to 1986, then at Obolensk until 1992, when he defected to the West. He later divulged much of the Soviet biological weapons program and settled in the United States.<ref>{{Cite web |title=Interviews with Biowarriors: Sergei Popov |website=PBS |url=https://www.pbs.org/wgbh/nova/bioterror/biow_popov.html}}</ref>
== See also == * Environmental microbiology * List of Legionnaires' disease outbreaks * Microbiomes of the built environment
== References == {{Reflist|30em}}
== External links == {{Commons category}} {{Wikispecies}} * [https://web.archive.org/web/20121225121713/http://www.ewgli.org/ European Working Group for Legionella Infections] * [https://www.cdc.gov/ncidod/dhqp/pdf/guidelines/Enviro_guide_03.pdf Centers for Disease Control and Prevention] – Procedure for Cleaning Cooling Towers and Related Equipment (pages 239 and 240 of 249) * [http://www.energy.ca.gov/2005publications/CEC-700-2005-025/CEC-700-2005-025.PDF California Energy Commission] {{Webarchive|url=https://web.archive.org/web/20170128021433/http://www.energy.ca.gov/2005publications/CEC-700-2005-025/CEC-700-2005-025.PDF |date=2017-01-28 }}{{dash}}Cooling Water Management Program Guidelines For Wet and Hybrid Cooling Towers at Power Plants * [https://web.archive.org/web/20120119093337/http://www.ashrae.org/publications/detail/14891#Gdl12/ ASHRAE Guideline] * [https://web.archive.org/web/20140901141126/http://www.legionellae.org/guidelines/guidelines.htm Guidelines for Control of ''Legionella'' in Ornamental Fountains] * [https://web.archive.org/web/20080611231131/http://www.hse.gov.uk/pubns/iacl27.pdf Employers Guidelines for prevention of ''Legionella'']
{{Taxonbar|from=Q158013}} {{Authority control}}
Category:Bacteria genera Category:Bacterial diseases Category:Gram-negative bacteria Category:Industrial hygiene Category:Legionellales Category:Pathogenic bacteria