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Microorganisms
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Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health
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Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Public Health Microbiology".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 40667

Special Issue Editors

Prof. Janet E. Stout

E-Mail Website
Guest Editor
Special Pathogens Laboratory and University of Pittsburgh, Pittsburgh, PA, USA
Interests: ending Legionnaires’ disease
Dr. Julianne L. Baron

E-Mail Website
Guest Editor
Special Pathogens Laboratory, Pittsburgh, PA, USA
Interests: Legionella; waterborne pathogens; molecular biology; microbiome

Special Issue Information

It has been over 40 years since the outbreak of deadly pneumonia among the delegates of the American Legion convention in Philadelphia, Pennsylvania. It was aptly named Legionnaires’ disease, and the scientific community has learned much about it and the bacteria that cause it. The importance of water as an environmental reservoir has been realized, and strategies to disinfect building water systems have been developed.

Numerous public and government agencies, including The National Academies of Sciences, Engineering, and Medicine, suggest that more research is needed on Legionella and more can be done to manage the risks of Legionella species to susceptible populations.

The aim of this Special Issue of Microorganisms is to present a collection of articles that provide a current snapshot of research in the Legionnaires’ disease field, including pathogenesis, proactive prevention, and public health response to this waterborne pathogen. This collection will provide novel and thought-provoking perspectives on topics ranging from disease identification and clinical surveillance; to environmental monitoring, disinfection, and detection; pathogenesis and virulence; challenges for public health response to outbreaks; and water management strategies. We invite you to submit original research articles, short communications, case reports, and review articles related to Legionella and Legionnaires’ disease to address these important research topics.

Prof.  Janet E. Stout
Dr. Julianne L. Baron
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Microorganisms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Legionella species
  • L. pneumophila
  • Pathogenesis
  • Environmental detection
  • Premise plumbing
  • Disinfection technologies
  • Diagnostic testing
  • Clinical surveillance
  • Methods for identification and isolation
  • Water management plans

Published Papers (11 papers)

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Research

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8 pages, 675 KiB  
Communication
Evaluation of Four Lateral Flow Assays for the Detection of Legionella Urinary Antigen
by Alicia Y. W. Wong, Alexander T. A. Johnsson, Aina Iversen, Simon Athlin and Volkan Özenci
Microorganisms 2021, 9(3), 493; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9030493 - 26 Feb 2021
Cited by 6 | Viewed by 3273
Abstract
Urinary antigen tests (UATs) are often used to diagnose Legionnaires’ disease as they are rapid and easy to perform on readily obtainable urine samples without the need for specialized skills compared to conventional methods. Recently developed automated readers for UATs may provide objective [...] Read more.
Urinary antigen tests (UATs) are often used to diagnose Legionnaires’ disease as they are rapid and easy to perform on readily obtainable urine samples without the need for specialized skills compared to conventional methods. Recently developed automated readers for UATs may provide objective results interpretation, especially in cases of weak result bands. Using 53 defined patient urine samples, we evaluated the performance of the BinaxNOW Legionella Antigen Card (Abbott), ImmuView S. pneumoniae and Legionella (SSI Diagnostica), STANDARD F Legionella Ag FIA (SD Biosensor), and Sofia Legionella FIA (Quidel) simultaneously with their respective automated readers. Automatic and visual interpretation of result bands were also compared for the immunochromatography-based BinaxNOW and ImmuView UATs. Overall sensitivity and specificity of Legionella UATs were 53.9–61.5% and 90.0–94.9%, respectively. All four UATs successfully detected all samples from L. pneumophila serogroup 1-positive patients, but most failed to detect samples for Legionella spp., or other serogroups. Automatic results interpretation of results was found to be mostly concordant with visual results reading. In conclusion, the performance of the four UATs were similar to each other in the detection of Legionella urinary antigen with no major difference between automated or visual results reading. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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13 pages, 1631 KiB  
Article
Development of a Fluorescent Tool for Studying Legionella bozemanae Intracellular Infection
by Breanne M. Head, Christopher I. Graham, Teassa MacMartin, Yoav Keynan and Ann Karen C. Brassinga
Microorganisms 2021, 9(2), 379; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9020379 - 13 Feb 2021
Cited by 2 | Viewed by 2347
Abstract
Legionnaires’ disease incidence is on the rise, with the majority of cases attributed to the intracellular pathogen, Legionella pneumophila. Nominally a parasite of protozoa, L. pneumophila can also infect alveolar macrophages when bacteria-laden aerosols enter the lungs of immunocompromised individuals. L. pneumophila pathogenesis [...] Read more.
Legionnaires’ disease incidence is on the rise, with the majority of cases attributed to the intracellular pathogen, Legionella pneumophila. Nominally a parasite of protozoa, L. pneumophila can also infect alveolar macrophages when bacteria-laden aerosols enter the lungs of immunocompromised individuals. L. pneumophila pathogenesis has been well characterized; however, little is known about the >25 different Legionella spp. that can cause disease in humans. Here, we report for the first time a study demonstrating the intracellular infection of an L. bozemanae clinical isolate using approaches previously established for L. pneumophila investigations. Specifically, we report on the modification and use of a green fluorescent protein (GFP)-expressing plasmid as a tool to monitor the L. bozemanae presence in the Acanthamoeba castellanii protozoan infection model. As comparative controls, L. pneumophila strains were also transformed with the GFP-expressing plasmid. In vitro and in vivo growth kinetics of the Legionella parental and GFP-expressing strains were conducted followed by confocal microscopy. Results suggest that the metabolic burden imposed by GFP expression did not impact cell viability, as growth kinetics were similar between the GFP-expressing Legionella spp. and their parental strains. This study demonstrates that the use of a GFP-expressing plasmid can serve as a viable approach for investigating Legionella non-pneumophila spp. in real time. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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12 pages, 1184 KiB  
Article
Healthcare-Associated Legionella Disease: A Multi-Year Assessment of Exposure Settings in a National Healthcare System in the United States
by Meredith Ambrose, Gary A. Roselle, Stephen M. Kralovic and Shantini D. Gamage
Microorganisms 2021, 9(2), 264; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9020264 - 28 Jan 2021
Cited by 2 | Viewed by 2190
Abstract
Healthcare facilities are high-risk environments for Legionella disease (LD), including Legionnaires’ disease, but transmission in these settings is often overlooked. We used the LD database at the U.S. Department of Veterans Affairs (VA) national healthcare system to assess the type of healthcare exposure [...] Read more.
Healthcare facilities are high-risk environments for Legionella disease (LD), including Legionnaires’ disease, but transmission in these settings is often overlooked. We used the LD database at the U.S. Department of Veterans Affairs (VA) national healthcare system to assess the type of healthcare exposure for LD cases. Cases were extracted from the database for 1 September 2012 through 31 July 2019, focusing on cases with an overnight stay at a VA facility during the 10-day exposure window prior to symptom onset. Patient medical charts were reviewed for demographics and types of healthcare setting exposure(s). There were 99 LD cases in the cohort: 31.3% were classified as having definite VA exposure, 37.4% were classified as possible VA with inpatient exposure, and 31.3% were classified as possible VA with both inpatient and outpatient exposure. For definite VA LD cases, 67.7% had some type of exposure in the long-term care setting. While 63% of the 99 cases had exposure in the acute care setting only, both the long-term care and acute care settings contributed substantially to the total number of exposure days. A review of patient movement during the exposure period showed the variable and sometimes extensive use of the VA system, and it provides insights useful for epidemiologic investigations and potential preventive actions. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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12 pages, 3973 KiB  
Article
Differential Bacterial Predation by Free-Living Amoebae May Result in Blooms of Legionella in Drinking Water Systems
by Mohamed Shaheen and Nicholas J. Ashbolt
Microorganisms 2021, 9(1), 174; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9010174 - 15 Jan 2021
Cited by 9 | Viewed by 2697
Abstract
Intracellular growth of pathogenic Legionella in free-living amoebae (FLA) results in the critical concentrations that are problematic in engineered water systems (EWS). However, being amoeba-resistant bacteria (ARB), how Legionella spp. becomes internalized within FLA is still poorly understood. Using fluorescent microscopy, we investigated [...] Read more.
Intracellular growth of pathogenic Legionella in free-living amoebae (FLA) results in the critical concentrations that are problematic in engineered water systems (EWS). However, being amoeba-resistant bacteria (ARB), how Legionella spp. becomes internalized within FLA is still poorly understood. Using fluorescent microscopy, we investigated in real-time the preferential feeding behavior of three water-related FLA species, Willaertia magna, Acanthamoeba polyphaga, and Vermamoeba vermiformis regarding Legionella pneumophila and two Escherichia coli strains. Although all the studied FLA species supported intracellular growth of L. pneumophila, they avoided this bacterium to a certain degree in the presence of E. coli and mostly fed on it when the preferred bacterial food-sources were limited. Moreover, once L. pneumophila were intracellular, it inhibited digestion of co-occurring E. coli within the same trophozoites. Altogether, based on FLA–bacteria interactions and the shifts in microbial population dynamics, we propose that FLA’s feeding preference leads to an initial growth of FLA and depletion of prey bacteria, thus increases the relative abundance of Legionella and creates a “forced-feeding” condition facilitating the internalization of Legionella into FLA to initiate the cycles of intracellular multiplication. These findings imply that monitoring of FLA levels in EWS could be useful in predicting possible imminent high occurrence of Legionella. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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12 pages, 2481 KiB  
Communication
A Methodology for Classifying Root Causes of Outbreaks of Legionnaires’ Disease: Deficiencies in Environmental Control and Water Management
by Benjamin R. Clopper, Jasen M. Kunz, Simone W. Salandy, Jessica C. Smith, Brian C. Hubbard and John P. Sarisky
Microorganisms 2021, 9(1), 89; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9010089 - 01 Jan 2021
Cited by 14 | Viewed by 4794
Abstract
We piloted a methodology for collecting and interpreting root cause—or environmental deficiency (ED)—information from Legionnaires’ disease (LD) outbreak investigation reports. The methodology included a classification framework to assess common failures observed in the implementation of water management programs (WMPs). We reviewed reports from [...] Read more.
We piloted a methodology for collecting and interpreting root cause—or environmental deficiency (ED)—information from Legionnaires’ disease (LD) outbreak investigation reports. The methodology included a classification framework to assess common failures observed in the implementation of water management programs (WMPs). We reviewed reports from fourteen CDC-led investigations between 1 January 2015 and 21 June 2019 to identify EDs associated with outbreaks of LD. We developed an abstraction guide to standardize data collection from outbreak reports and define relevant parameters. We categorized each ED according to three criteria: ED type, WMP-deficiency type, and source of deficiency. We calculated the prevalence of EDs among facilities and explored differences between facilities with and without WMPs. A majority of EDs identified (81%) were classified as process failures. Facilities with WMPs (n = 8) had lower prevalence of EDs attributed to plumbed devices (9.1%) and infrastructure design (0%) than facilities without WMPs (n = 6; 33.3% and 24.2%, respectively). About three quarters (72%) of LD cases and 81% of the fatalities in our sample originated at facilities without a WMP. This report highlights the importance of WMPs in preventing and mitigating outbreaks of LD. Building water system process management is a primary obstacle toward limiting the root causes of LD outbreaks. Greater emphasis on the documentation, verification, validation, and continuous program review steps will be important in maximizing the effectiveness of WMPs. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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11 pages, 952 KiB  
Article
Evaluation of Recommended Water Sample Collection Methods and the Impact of Holding Time on Legionella Recovery and Variability from Healthcare Building Water Systems
by Marisa B. Hirsh, Julianne L. Baron, Sue M. Mietzner, John D. Rihs, Mohamed H. Yassin and Janet E. Stout
Microorganisms 2020, 8(11), 1770; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms8111770 - 11 Nov 2020
Cited by 8 | Viewed by 3375
Abstract
Water safety and management programs (WSMP) utilize field measurements to evaluate control limits and monitor water quality parameters including Legionella presence. This monitoring is important to verify that the plan is being implemented properly. However, once it has been determined when and how [...] Read more.
Water safety and management programs (WSMP) utilize field measurements to evaluate control limits and monitor water quality parameters including Legionella presence. This monitoring is important to verify that the plan is being implemented properly. However, once it has been determined when and how to sample for Legionella, it is important to choose appropriate collection and processing methods. We sought to compare processing immediate and flushed samples, filtration of different volumes collected, and sample hold times. Hot water samples were collected immediately and after a 2-min flush. These samples were plated directly and after filtration of either 100 mL, 200 mL, or 1 L. Additionally, unflushed samples were collected and processed immediately and after 1, 24, and 48 h of hold time. We found that flushed samples had significant reductions in Legionella counts compared to immediate samples. Processing 100 mL of that immediate sample both directly and after filter concentration yielded the highest concentration and percent sample positivity, respectively. We also show that there was no difference in culture values from time 0 compared to hold times of 1 h and 24 h. At 48 h, there were slightly fewer Legionella recovered than at time 0. However, Legionella counts were so variable based on sampling location and date that this hold time effect was minimal. The interpretation of Legionella culture results depends on the sample collection and processing methods used, as these can have a huge impact on the success of sampling and the validation of control measures. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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17 pages, 2332 KiB  
Article
Chlorine Disinfection of Legionella spp., L. pneumophila, and Acanthamoeba under Warm Water Premise Plumbing Conditions
by Rebekah L. Martin, Kara Harrison, Caitlin R. Proctor, Amanda Martin, Krista Williams, Amy Pruden and Marc A. Edwards
Microorganisms 2020, 8(9), 1452; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms8091452 - 22 Sep 2020
Cited by 9 | Viewed by 3450
Abstract
Premise plumbing conditions can contribute to low chlorine or chloramine disinfectant residuals and reactions that encourage opportunistic pathogen growth and create risk of Legionnaires’ Disease outbreaks. This bench-scale study investigated the growth of Legionella spp. and Acanthamoeba in direct contact with premise plumbing [...] Read more.
Premise plumbing conditions can contribute to low chlorine or chloramine disinfectant residuals and reactions that encourage opportunistic pathogen growth and create risk of Legionnaires’ Disease outbreaks. This bench-scale study investigated the growth of Legionella spp. and Acanthamoeba in direct contact with premise plumbing materials—glass-only control, cross-linked polyethylene (PEX) pipe, magnesium anode rods, iron pipe, iron oxide, pH 10, or a combination of factors. Simulated glass water heaters (SGWHs) were colonized by Legionella pneumophila and exposed to a sequence of 0, 0.1, 0.25, and 0.5 mg/L chlorine or chloramine, at two levels of total organic carbon (TOC), over 8 weeks. Legionella pneumophila thrived in the presence of the magnesium anode by itself and or combination with other factors. In most cases, 0.5 mg/L Cl2 caused a significant rapid reduction of L. pneumophila, Legionella spp., or total bacteria (16S rRNA) gene copy numbers, but at higher TOC (>1.0 mg C/L), a chlorine residual of 0.5 mg/L Cl2 was not effective. Notably, Acanthamoeba was not significantly reduced by the 0.5 mg/L chlorine dose. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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Review

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22 pages, 1188 KiB  
Review
Environmental Management of Legionella in Domestic Water Systems: Consolidated and Innovative Approaches for Disinfection Methods and Risk Assessment
by Emanuele Luigi Sciuto, Pasqualina Laganà, Simona Filice, Silvia Scalese, Sebania Libertino, Domenico Corso, Giuseppina Faro and Maria Anna Coniglio
Microorganisms 2021, 9(3), 577; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9030577 - 11 Mar 2021
Cited by 21 | Viewed by 4314
Abstract
Legionella is able to remain in water as free-living planktonic bacteria or to grow within biofilms that adhere to the pipes. It is also able to enter amoebas or to switch into a viable but not culturable (VBNC) state, which contributes to its [...] Read more.
Legionella is able to remain in water as free-living planktonic bacteria or to grow within biofilms that adhere to the pipes. It is also able to enter amoebas or to switch into a viable but not culturable (VBNC) state, which contributes to its resistance to harsh conditions and hinders its detection in water. Factors regulating Legionella growth, such as environmental conditions, type and concentration of available organic and inorganic nutrients, presence of protozoa, spatial location of microorganisms, metal plumbing components, and associated corrosion products are important for Legionella survival and growth. Finally, water treatment and distribution conditions may affect each of these factors. A deeper comprehension of Legionella interactions in water distribution systems with the environmental conditions is needed for better control of the colonization. To this purpose, the implementation of water management plans is the main prevention measure against Legionella. A water management program requires coordination among building managers, health care providers, and Public Health professionals. The review reports a comprehensive view of the state of the art and the promising perspectives of both monitoring and disinfection methods against Legionella in water, focusing on the main current challenges concerning the Public Health sector. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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17 pages, 555 KiB  
Review
Legionellosis Caused by Non-Legionella pneumophila Species, with a Focus on Legionella longbeachae
by Stephen T. Chambers, Sandy Slow, Amy Scott-Thomas and David R. Murdoch
Microorganisms 2021, 9(2), 291; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9020291 - 31 Jan 2021
Cited by 28 | Viewed by 5629
Abstract
Although known as causes of community-acquired pneumonia and Pontiac fever, the global burden of infection caused by Legionella species other than Legionella pneumophila is under-recognised. Non-L. pneumophila legionellae have a worldwide distribution, although common testing strategies for legionellosis favour detection of L. [...] Read more.
Although known as causes of community-acquired pneumonia and Pontiac fever, the global burden of infection caused by Legionella species other than Legionella pneumophila is under-recognised. Non-L. pneumophila legionellae have a worldwide distribution, although common testing strategies for legionellosis favour detection of L. pneumophila over other Legionella species, leading to an inherent diagnostic bias and under-detection of cases. When systematically tested for in Australia and New Zealand, L. longbeachae was shown to be a leading cause of community-acquired pneumonia. Exposure to potting soils and compost is a particular risk for infection from L. longbeachae, and L. longbeachae may be better adapted to soil and composting plant material than other Legionella species. It is possible that the high rate of L. longbeachae reported in Australia and New Zealand is related to the composition of commercial potting soils which, unlike European products, contain pine bark and sawdust. Genetic studies have demonstrated that the Legionella genomes are highly plastic, with areas of the chromosome showing high levels of recombination as well as horizontal gene transfer both within and between species via plasmids. This, combined with various secretion systems and extensive effector repertoires that enable the bacterium to hijack host cell functions and resources, is instrumental in shaping its pathogenesis, survival and growth. Prevention of legionellosis is hampered by surveillance systems that are compromised by ascertainment bias, which limits commitment to an effective public health response. Current prevention strategies in Australia and New Zealand are directed at individual gardeners who use potting soils and compost. This consists of advice to avoid aerosols generated by the use of potting soils and use masks and gloves, but there is little evidence that this is effective. There is a need to better understand the epidemiology of L. longbeachae and other Legionella species in order to develop effective treatment and preventative strategies globally. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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10 pages, 237 KiB  
Review
Living with Legionella and Other Waterborne Pathogens
by Joseph O. Falkinham III
Microorganisms 2020, 8(12), 2026; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms8122026 - 18 Dec 2020
Cited by 25 | Viewed by 3662
Abstract
Legionella spp. and other opportunistic premise plumbing pathogens (OPPPs), including Pseudomonas aeruginosa, Mycobacterium avium, Stenotrophomonas maltophilia, and Acinetobacter baumannii, are normal inhabitants of natural waters, drinking water distribution systems and premise plumbing. Thus, humans are regularly exposed to these [...] Read more.
Legionella spp. and other opportunistic premise plumbing pathogens (OPPPs), including Pseudomonas aeruginosa, Mycobacterium avium, Stenotrophomonas maltophilia, and Acinetobacter baumannii, are normal inhabitants of natural waters, drinking water distribution systems and premise plumbing. Thus, humans are regularly exposed to these pathogens. Unfortunately, Legionella spp. and the other OPPPs share a number of features that allow them to grow and persist in premise plumbing. They form biofilms and are also relatively disinfectant-resistant, able to grow at low organic matter concentrations, and able to grow under stagnant conditions. Infections have been traced to exposure to premise plumbing or aerosols generated in showers. A number of measures can lead to reduction in OPPP numbers in premise plumbing, including elevation of water heater temperatures. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)

Other

Jump to: Research, Review

15 pages, 2474 KiB  
Project Report
Rapid Testing and Interventions to Control Legionella Proliferation following a Legionnaires’ Disease Outbreak Associated with Cooling Towers
by Charlotte Young, Duncan Smith, Tim Wafer and Brian Crook
Microorganisms 2021, 9(3), 615; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9030615 - 17 Mar 2021
Cited by 7 | Viewed by 3630
Abstract
Most literature to date on the use of rapid Legionella tests have compared different sampling and analytical techniques, with few studies on real-world experiences using such methods. Rapid tests offer a significantly shorter feedback loop on the effectiveness of the controls. This study [...] Read more.
Most literature to date on the use of rapid Legionella tests have compared different sampling and analytical techniques, with few studies on real-world experiences using such methods. Rapid tests offer a significantly shorter feedback loop on the effectiveness of the controls. This study involved a complex of five factories, three of which had a history of Legionella contamination in their cooling water distribution system. Multiple sampling locations were utilised to take monthly water samples over 39 months to analyse for Legionella by both culture and quantitative polymerase chain reaction (qPCR). Routine monitoring gave no positive Legionella results by culture (n = 330); however, samples were frequently (68%) positive by qPCR for Legionella spp. (n = 1564). Legionella spp. qPCR assay was thus found to be a good indicator of cooling tower system health and suitable as a routine monitoring tool. An in-house qPCR limit of 5000 genomic units (GU)/L Legionella spp. was established to trigger investigation and remedial action. This approach facilitated swift remedial action to prevent Legionella proliferation to levels that may represent a public health risk. Cooling tower operators may have to set their own action levels for their own systems; however, in this study, 5000 GU/L was deemed appropriate and pragmatic. Full article
(This article belongs to the Special Issue Legionella and Legionnaires’ Disease: Pathogenesis, Prevention, and Public Health)
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