Clinical and Laboratory Diagnosis of Legionella Pneumonia

Legionella pneumonia is a relatively rare but extremely progressive pulmonary infection with high mortality. Traditional cultural isolation remains the gold standard for the diagnosis of Legionella pneumonia. However, its harsh culture conditions, long turnaround time, and suboptimal sensitivity do not meet the clinical need for rapid and accurate diagnosis, especially for critically ill patients. So far, pathogenic detection techniques including serological assays, urinary antigen tests, and mass spectrometry, as well as nucleic acid amplification technique, have been developed, and each has its own advantages and limitations. This review summarizes the clinical characteristics and imaging findings of Legionella pneumonia, then discusses the advances, advantages, and limitations of the various pathogenetic detection techniques used for Legionella pneumonia diagnosis. The aim is to provide rapid and accurate guiding options for early identification and diagnosis of Legionella pneumonia in clinical practice, further easing healthcare burden.

Extensive epigenetic modification with large-scale chromosomal and plasmid recombination characterise the Legionella longbeachae serogroup 1 genome

Legionella longbeachae is an environmental bacterium that is the most clinically significant Legionella species in New Zealand (NZ), causing around two-thirds of all notified cases of Legionnaires’ disease. Here we report the sequencing and analysis of the geo-temporal genetic diversity of 54 L. longbeachae serogroup 1 (sg1) clinical isolates, derived from cases from around NZ over a 22-year period, including one complete genome and its associated methylome. The 54 sg1 isolates belonged to two main clades that last shared a common ancestor between 95 BCE and 1694 CE. There was diversity at the genome-structural level, with large-scale arrangements occurring in some regions of the chromosome and evidence of extensive chromosomal and plasmid recombination. This includes the presence of plasmids derived from recombination and horizontal gene transfer between various Legionella species, indicating there has been both intra- and inter-species gene flow. However, because similar plasmids were found among isolates within each clade, plasmid recombination events may pre-empt the emergence of new L. longbeachae strains. Our complete NZ reference genome consisted of a 4.1 Mb chromosome and a 108 kb plasmid. The genome was highly methylated with two known epigenetic modifications, m⁴C and m⁶A, occurring in particular sequence motifs within the genome.

Risk assessment and quantitative measurement along with monitoring of Legionella in hospital water sources

Legionella spp. as a causative agent of Legionnaires' disease (LD) and an opportunistic pathogen creates a public health problem. Isolation and quantification of this bacteria from clinic water sources are essential for hazard appraisal and sickness avoidance. This study aimed at risk assessment and quantitative measurement along with Legionella monitoring in educational hospital water sources in Tehran, Iran. A cross-sectional study was carried out in 1 year. The conventional culture method was used in this study to isolate Legionella from water samples. The polymerase chain reaction (PCR) technique was used to confirm the identity of the isolates and ensure that they were all Legionella. Quantitative PCR (qPCR) was used to determine the count of bacteria, and HeLa cell culture was used to determine the invasion of isolates. A total of 100 water samples were collected and inoculated on GVPC (glycine, vancomycin, polymyxin, and cycloheximide) agar; 12 (12%) and 42 (42%) cases were culture and PCR positive, respectively. Percentage of Legionella presence in PCR-positive samples by the qPCR method in <10³ GU/L, in about 10³ and lower than 10⁴ GU/L, and in 10⁴ GU/L was 40.47 (17 cases), 4.76% (two cases), and 54.76% (23 cases), respectively. Invasion analysis revealed that five and four isolates had invaded HeLa cells more than twice and equally, respectively, and the others had a lower invasion than the reference strain. The findings revealed that the spread of LD in hospitals was linked to the water system. Given the importance of nosocomial infections in the medical community, establishing a hospital water monitoring system is the most effective way to control these infections, particularly Legionella infections.

Legionella feeleii: Ubiquitous Pathogen in the Environment and Causative Agent of Pneumonia

L. feeleii is one of the most frequent Legionella species isolated from natural pools of the central region of Spain. This study aimed to evaluate its ecology and to identify this Legionella species as a respiratory pathogen. A PCR assay for detecting the L. feeleii mip gene was developed to identify it in clinical and environmental samples. Culture and PCR were performed in environmental samples from four drinking water treatment plants (DWTPs). Free L. feeleii was only detected in raw water samples (3.4%), while L. feeleii as an Acanthamoeba endosymbiont was found in 30.7% of raw water, 11.5% of decanter biofilm, and 32% of finished water samples. Therefore, Acanthamoeba spp. plays an essential role in the multiplication, persistence, and spread of Legionella species in the environment. The first case of Legionnaires’ disease caused by L. feeleii in Spain is described in this study. The case was diagnosed in an older woman through PCR and sequencing from urine and sputum samples. A respiratory infection could be linked with health care procedures, and the patient presented several risk factors (age, insulin-dependent diabetes, and heart disease). The detection of non-L. pneumophila, such as L. feeleii, is a factor that must be considered when establishing or reviewing measures for the control and prevention of legionellosis.

How safe are gloves and masks used for protection against Legionella longbeachae infection when gardening?

Legionella longbeachae has been frequently identified in composted plant material and can cause Legionnaires' disease (LD). We wanted to determine how frequently L. longbeachae DNA was present on gardeners' gloves, and how long L. longbeachae could persist on inoculated gloves and masks. Volunteers completed a survey of gardening practices and their gardening gloves were tested for L. longbeachae DNA by qPCR. The persistence of viable L. longbeachae was assessed by timed subcultures after inoculation of gardening gloves and masks. Gloves but not masks were used regularly. L. longbeachae was detected on 11 (14%; 95% CI 8-24%) gloves. Viable organisms were recovered from 25-50% of inoculated cotton, leather and PU coated gloves but not rubber gloves after 8 h incubation. There was a difference in dose-response curve slopes by glove material (P = 0·001) and time to 50% sterility (P = 0·036). There were differences in persistence of L. longbeachae between mask types from analysis of the slopes and 50% sterility on the decay curves (P = 0·042, P < 0·001 respectively). Gardening gloves and masks may act as a vector for transmission of L. longbeachae during gardening. Washing gardening gloves and prompt disposal of masks could reduce risk of LD.

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In September 2018 in Brescia province, northern Italy, an outbreak of Legionnaires' disease (LD) caused by Legionella pneumophila serogroup 2 (Lp2) occurred. The 33 cases (two fatal) resided in seven municipalities along the Chiese river. All cases were negative by urinary antigen test (UAT) and most were diagnosed by real-time PCR and serology. In only three cases, respiratory sample cultures were positive, and Lp2 was identified and typed as sequence type (ST)1455. In another three cases, nested sequence-based typing was directly applied to respiratory samples, which provided allelic profiles highly similar to ST1455. An environmental investigation was undertaken immediately and water samples were collected from private homes, municipal water systems, cooling towers and the river. Overall, 533 environmental water samples were analysed and 34 were positive for Lp. Of these, only three samples, all collected from the Chiese river, were Lp2 ST1455. If and how the river water could have been aerosolised causing the LD cases remains unexplained. This outbreak, the first to our knowledge caused by Lp2, highlights the limits of UAT for LD diagnosis, underlining the importance of adopting multiple tests to ensure that serogroups other than serogroup 1, as well as other Legionella species, are identified.

Quantification of Legionella pneumophila by qPCR and culture in tap water with different concentrations of residual disinfectants and heterotrophic bacteria

Legionellosis prevalence is increasing in the United States. This disease is caused primarily by the bacterium Legionella pneumophila found in water and transmitted by aerosol inhalation. This pathogen has a slow growth rate and can "hide" in amoeba, making it difficult to monitor by the traditional culture method on selective media. Tap water samples (n = 358) collected across the United States were tested for L. pneumophila by both culture and quantitative Polymerase Chain Reaction (qPCR). The presence of other bacteria was quantified by heterotrophic plate counts (HPC). Residual disinfectant concentrations (free chlorine or monochloramine) were measured in all samples. Legionella pneumophila had the highest prevalence and concentration in the chlorinated water samples that had a free‑chlorine value of less than 0.2 mg Cl₂/L. In total, 24% (87/358) of the samples were positive for L. pneumophila either by qPCR or 3% (11/358) were positive by culture. In chloramine-treated samples, L. pneumophila was detected by qPCR in 21% (31/148) and 1% (2/148) by culture, despite a high monochloramine residual >1 mg Cl₂/L. Despite the presence of a high disinfectant residual (>1 mg Cl₂/L), HPC counts were substantial. This study indicates that both culture and qPCR methods have limitations when predicting a potential risk for disease associated with L. pneumophila in tap water. Measuring disinfectant residuals and quantifying HPC in water samples may be useful adjunct parameters for reducing Legionellosis' risk from public water supplies at high-risk locations.

An outbreak investigation of Legionella non-pneumophila Legionnaires’ disease in Sweden, April to August 2018: Gardening and use of commercial bagged soil associated with infections

In early June 2018, an increase in non-travel-related cases of Legionella non-pneumophila Legionnaires’ disease (LD) was observed in Sweden and a national outbreak investigation was started. Outbreak cases were defined as notified confirmed or probable cases of L. non-pneumophila LD, with symptom onset after 1 April 2018. From April to August 2018, 41 cases were reported, 30 of whom were identified as L. longbeachae. We conducted a case–control study with 27 cases and 182 matched controls. Results from the case–control study indicated that gardening and handling commercial bagged soil, especially dusty dry soil, were associated with disease. L. longbeachae was isolated in soils from cases’ homes or gardens, but joint analysis of soil and human specimens did not identify any genetic clonality. Substantial polyclonality was noted between and within soil samples, which made finding a genetic match between soil and human specimens unlikely. Therefore, whole genome sequencing may be of limited use to confirm a specific soil as a vehicle of transmission for L. longbeachae. Handling soil for residential gardening was associated with disease and the isolation of L. longbeachae in different soils provided further evidence for Legionella non-pneumophila infection from soil.

Legionellosis Caused by Non-Legionella pneumophila Species, with a Focus on Legionella longbeachae

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.

Legionella pneumophila as a cause of cavitary lung disease in systemic lupus erythematous

Legionnaire's disease (LD) is most commonly caused by Legionella pneumophila (L. pneumophila). In immunocompromised patients LD can cause necrosis of the lung parenchyma with abscess formation and cavitation. Systemic lupus erythematosus (SLE) is an autoimmune disorder with features of both primary and secondary immunodeficiency. SLE patients often develop pulmonary abnormalities, but rarely develop lung cavitations. We report a case of cavitary pneumonia caused by L. pneumophila in a 64-year-old female patient with SLE. We also highlight reasons why SLE patients are more prone to L. pneumophila infections. The importance of using correct diagnostic methods for recognizing and treating such infections is also discussed, as mistreatment of cavitary lesions in SLE patients with steroid therapy can have fatal outcomes as the infectious process can significantly worsen.

Legionella longbeachae pneumonia: A case report and literature review in Japan

Herein, we report the case of a 74-year-old man diagnosed with Legionella pneumonia detected by Loop-Mediated Isothermal Amplification (LAMP) method, which was suspected to have been transmitted from the potting soil. Legionella longbeachae was identified in the sputum culture. The patient was intubated and maintained on mechanical ventilation. Antimicrobial therapy with azithromycin was also administered. His symptoms were resolved and he was discharged after 26 days of hospitalization. Legionella longbeachae pneumonia rarely occurs in Japan, and published literature of Legionella longbeachae pneumonia cases in Japan was reviewed. Patients with severe pneumonia exposed to potting soils, but with negative urinary antigen test results, should be examined by LAMP method.

Risk Factors, Management, and Outcomes of Legionella Pneumonia in a Large, Nationally Representative Sample

BACKGROUND

American Thoracic Society/Infectious Diseases Society of America guidelines recommend against routine Legionella pneumophila testing, but recommend that hospitalized patients with community-acquired pneumonia receive empiric treatment covering Legionella. Testing, empiric treatment, and outcomes for patients with Legionella have not been well described.

RESEARCH QUESTION

Is testing for Legionella pneumophila appropriate, and could it impact treatment?

STUDY DESIGN AND METHODS

We conducted a large retrospective cohort analysis using Premier Healthcare Database data from 2010 to 2015. We included adults with a principal diagnosis code for pneumonia (or a principal diagnosis of respiratory failure or sepsis with secondary diagnosis of pneumonia) if they also received treatment for pneumonia on hospital days 1-3. We categorized Legionella-tested patients by test result, identified patient characteristics associated with testing and test result, and examined seasonal and regional patterns of Legionella pneumonia (LP) diagnoses. Empiric therapy for LP was defined as a macrolide, quinolone, or doxycycline, administered on each of the first two hospital days.

RESULTS

Of 166,689 eligible patients, 43,070 (26%) were tested for Legionella, and 642 (1.5%) tested positive. Although only 36% of tests were ordered from June to October, 70% of positive test results occurred during this time. Only 30% of patients with hyponatremia, 32% with diarrhea, and 27% in the ICU were tested. Of patients with positive test results, 495 of 642 (77%) had received empiric Legionella therapy. Patients with LP did not have more severe presentation. They had more frequent late decompensation, but similar mortality to patients without LP.

INTERPRETATION

Legionella is an uncommon cause of community-acquired pneumonia, occurring primarily from late spring through early autumn. Testing is uncommon, even among patients with risk factors, and many patients with positive test results failed to receive empiric coverage for LP.

Enhancement of Culture of Legionella longbeachae from Respiratory Samples by Use of Immunomagnetic Separation and Antimicrobial Decontamination

Legionella longbeachae is the commonest Legionella species identified in patients with community-acquired pneumonia in New Zealand. Isolation of the organism on culture is the gold standard for the diagnosis of Legionnaires disease, but it has poor sensitivity (40%) compared with quantitative PCR (qPCR). We have developed a selective decontamination process using glycine, vancomycin, polymyxin, and cycloheximide (GVPC) with immunomagnetic separation (IMS) for culturing L. longbeachae A polyclonal antibody specific for L. longbeachae was produced from New Zealand White rabbits and coupled to tosyl-activated magnetic beads. Stored L. longbeachae qPCR-positive respiratory samples were retrieved from -80°C storage for testing. One portion of test samples was mixed with GVPC and the antibody bead complex, separated, washed, and cultured on modified Wadowsky and Yee agar (MWY) agar. Another portion was exposed to HCl-KCl acidic buffer (pH 2.2) before incubation on MWY agar. qPCR used probes specific for the ITS (internal transcribed spacer) region of the L. longbeachae genome. Cultures were positive in 10/53 (19%) samples after acid wash and 26/53 (49%) after GVPC-IMS (P = 0.001). Growth of contaminants was rare. The mean qPCR threshold cycle values were lower in culture-positive samples after acid wash than in the culture-negative samples (mean, 29.9 versus 34.8; difference, 4.9; 95% confidence interval [CI], ±2.9; P = 0.001) but not after GVPC-IMS (mean, 33.0 versus 34.7; difference, 1.7; 95% CI, ±2.48; P = 0.16). The sensitivity of culture for L. longbeachae in respiratory specimens may be improved by using GVPC-IMS rather than acid wash for decontamination, but this should be confirmed in a prospective study of fresh specimens.

Complete Genome Sequence of a Legionella longbeachae Serogroup 2 Isolate Derived from a Patient with Legionnaires' Disease

Legionella longbeachae is the predominant cause of Legionnaires’ disease (LD) in New Zealand. Although serogroup 2 (sg2) does not contain the most clinically significant strain, it is an important cause of disease. Here, we report the complete genome sequence of an sg2 isolate from a patient who was hospitalized with LD.

Legionella longbeachae is the predominant cause of Legionnaires’ disease (LD) in New Zealand. Although serogroup 2 (sg2) does not contain the most clinically significant strain, it is an important cause of disease. Here, we report the complete genome sequence of an sg2 isolate from a patient who was hospitalized with LD.

Legionnaires’ Disease: State of the Art Knowledge of Pathogenesis Mechanisms of Legionella

Legionella species are environmental gram-negative bacteria able to cause a severe form of pneumonia in humans known as Legionnaires’ disease. Since the identification of Legionella pneumophila in 1977, four decades of research on Legionella biology and Legionnaires’ disease have brought important insights into the biology of the bacteria and the molecular mechanisms that these intracellular pathogens use to cause disease in humans. Nowadays, Legionella species constitute a remarkable model of bacterial adaptation, with a genus genome shaped by their close coevolution with amoebae and an ability to exploit many hosts and signaling pathways through the secretion of a myriad of effector proteins, many of which have a eukaryotic origin. This review aims to discuss current knowledge of Legionella infection mechanisms and future research directions to be taken that might answer the many remaining open questions. This research will without a doubt be a terrific scientific journey worth taking.

Molecular testing for respiratory pathogens in sickle cell disease adult patients presenting with febrile acute chest syndrome

BACKGROUND

Differentiating acute chest syndrome (ACS) from community-acquired pneumonia (CAP) is challenging in adults presenting with major sickle cell disease (SCD) (semiological similarity, rare microbiological documentation). We aimed to assess the usefulness of nucleic acid amplification test (NAAT) for respiratory pathogens, in combination with standard bacteriological investigations, in febrile ACS adult patients presenting with major SCD.

METHODS

We performed a prospective, monocentric, observational study of 61 SCD adults presenting with febrile ACS from February 2015 to April 2016. Systematic blood, urine, and respiratory specimens were collected, before antibiotic initiation, for culture, urinary antigen tests, serology, and NAAT for respiratory pathogens.

RESULTS

A pathogen was detected in 12 febrile ACS (19.7%): four viruses (6.6%) (Rhinovirus; Influenza A/B), seven bacteria (11.4%) (S. aureus, S. pneumoniae, K. pneumoniae, L. pneumophila, M. pneumoniae), one mixed infection (1.6%) (S. aureus and Influenza B). NAAT only detected L. pneumophila in one case (serogroup 2). Apart from a significantly shorter antibiotic therapy duration (6.1 vs. 7.8 days, P=0.045), no difference was observed between undocumented and microbiologically-documented febrile ACS.

CONCLUSION

Using NAAT for the detection of respiratory pathogens in adults presenting with SCD slightly improved the microbiological diagnostic of febrile ACS, although respiratory infections are not the main etiological factor.

Legionella and Legionnaires' disease: Time to explore in India

Legionella pneumophila was first recognised as a fatal cause of pneumonia more than four decades ago, during the 1976-American Legion convention in Philadelphia, USA. Legionella spp. continue to cause disease outbreaks of public health significance, and at present, Legionnaires' disease (LD) has emerged as an important cause of community and hospital-acquired pneumonia. Parallel to this, the understanding of LD has also increased exponentially. However, the disease is likely to be underreported in many countries because of the dearth of common definitions, diagnostic tests and active surveillance systems. In this review, we outline the basic concepts of Legionella including clinical presentations, epidemiology, laboratory diagnosis and the status of LD in India. This article also summarises the progress of research related to Legionella in this country, identifying the research gaps and discussing priorities to explore this unexplored pathogen in India.

Improvement of Legionnaires' disease diagnosis using real-time PCR assay: a retrospective analysis, Italy, 2010 to 2015

AimTo evaluate real-time PCR as a diagnostic method for Legionnaires' disease (LD). Detection of Legionella DNA is among the laboratory criteria of a probable LD case, according to the European Centre for Disease Prevention and Control, although the utility and advantages, as compared to culture, are widely recognised.MethodsTwo independent laboratories, one using an in-house and the other a commercial real-time PCR assay, analysed 354 respiratory samples from 311 patients hospitalised with pneumonia between 2010-15. The real-time PCR reliability was compared with that of culture and urinary antigen tests (UAT). Concordance, specificity, sensitivity and positive and negative predictive values (PPV and NPV, respectively) were calculated.ResultsOverall PCR detected eight additional LD cases, six of which were due to Legionella pneumophila (Lp) non-serogroup 1. The two real-time PCR assays were concordant in 99.4% of the samples. Considering in-house real-time PCR as the reference method, specificity of culture and UAT was 100% and 97.9% (95% CI: 96.2-99.6), while the sensitivity was 63.6% (95%CI: 58.6-68.6) and 77.8% (95% CI: 72.9-82.7). PPV and NPV for culture were 100% and 93.7% (95% CI: 91.2-96.3). PPV and NPV for UAT were 87.5% (95% CI: 83.6-91.4) and 95.8% (95% CI: 93.5-98.2).ConclusionRegardless of the real-time PCR assay used, it was possible to diagnose LD cases with higher sensitivity than using culture or UAT. These data encourage the adoption of PCR as routine laboratory testing to diagnose LD and such methods should be eligible to define a confirmed LD case.

Clinical utility of pan-microbial PCR assays in the routine diagnosis of infectious diseases

The goals of the study were to examine the analytical properties and the clinical utility of pan-microbial PCR (PM-PCR) assays in a retrospective study conducted in 2014-2015 at the Tel-Aviv Sourasky Medical Center. PM-PCR included in-house assays for pan-bacterial, pan-fungal, and pan-mycobacterial PCR followed by sequencing. The clinical utility of the assays was decided based on defined criteria/categories. There were 585 PM-PCR tests performed on samples from 306 patients. The positivity rates of PM-PCR for bacterial, fungal, and mycobacterial infections were 72/316 (22.7%), 16/186 (8.6%), and 6/83 (7.2%), and the sensitivity values were 65%, 76%, and 85%, respectively. PCR results had influenced the management in 14/82 (17%) of PCR-positive cases and in 13/222 (5.8%) of PCR-negative cases (P = 0.005). The causes for the low clinical utility were related to lack of effect on the initial treatment in PCR-negative cases and concurrent positive cultures or presumed contamination in PCR-positive cases.

The Diagnosis of Legionella pneumophila Serogroup 5 Bacteremic Pneumonia during Severe Neutropenia Using Loop-mediated Isothermal Amplification

A 60-year-old man developed pneumonia after undergoing autologous peripheral blood stem cell transplantation for diffuse large-B cell lymphoma. A urinary antigen test and sputum culture were both negative for Legionella pneumophila; however, a sputum sample that was examined by loop-mediated isothermal amplification (LAMP) was positive for Legionella spp. On admission, the results of blood culturing using a BACTEC system were negative for 7 days. However, L. pneumophila serogroup 5 was detected in a blood subculture using WYOα medium. The patient was successfully treated with a fluoroquinolone-based regimen. LAMP is useful for the diagnosis of Legionella spp.

Risk Factors for Legionella longbeachae Legionnaires' Disease, New Zealand

Gardeners with chronic obstructive pulmonary disease or a history of smoking should take extra precautions to prevent infection.

Legionella longbeachae, found in soil and compost-derived products, is a globally underdiagnosed cause of Legionnaires’ disease. We conducted a case–control study of L. longbeachae Legionnaires’ disease in Canterbury, New Zealand. Case-patients were persons hospitalized with L. longbeachae pneumonia, and controls were persons randomly sampled from the electoral roll for the area served by the participating hospital. Among 31 cases and 172 controls, risk factors for Legionnaires’ disease were chronic obstructive pulmonary disease, history of smoking >10 years, and exposure to compost or potting mix. Gardening behaviors associated with L. longbeachae disease included having unwashed hands near the face after exposure to or tipping and troweling compost or potting mix. Mask or glove use was not protective among persons exposed to compost-derived products. Precautions against inhaling compost and attention to hand hygiene might effectively prevent L. longbeachae disease. Long-term smokers and those with chronic obstructive pulmonary disease should be particularly careful.

Ten Questions Concerning the Aerosolization and Transmission of Legionella in the Built Environment

Legionella is a genus of pathogenic Gram-negative bacteria responsible for a serious disease known as legionellosis, which is transmitted via inhalation of this pathogen in aerosol form. There are two forms of legionellosis: Legionnaires' disease, which causes pneumonia-like symptoms, and Pontiac fever, which causes influenza-like symptoms. Legionella can be aerosolized from various water sources in the built environment including showers, faucets, hot tubs/swimming pools, cooling towers, and fountains. Incidence of the disease is higher in the summertime, possibly because of increased use of cooling towers for air conditioning systems and differences in water chemistry when outdoor temperatures are higher. Although there have been decades of research related to Legionella transmission, many knowledge gaps remain. While conventional wisdom suggests that showering is an important source of exposure in buildings, existing measurements do not provide strong support for this idea. There has been limited research on the potential for Legionella transmission through heating, ventilation, and air conditioning (HVAC) systems. Epidemiological data suggest a large proportion of legionellosis cases go unreported, as most people who are infected do not seek medical attention. Additionally, controlled laboratory studies examining water-to-air transfer and source tracking are still needed. Herein, we discuss ten questions that spotlight current knowledge about Legionella transmission in the built environment, engineering controls that might prevent future disease outbreaks, and future research that is needed to advance understanding of transmission and control of legionellosis.

Microbiology and Epidemiology of Legionnaire's Disease

Legionnaire's disease (LD) is the pneumonic form of legionellosis caused by aerobic gram-negative bacilli of the genus Legionella. Individuals become infected when they inhale aerosolized water droplets contaminated with Legionella species. Forty years after the identification of Legionella pneumophila as the cause of the 1976 pneumonia outbreak in a hotel in Philadelphia, we have non-culture-based diagnostic tests, effective antibiotics, and preventive measures to handle LD. With a mortality rate still around 10%, underreporting, and sporadic outbreaks, there is still much work to be done. In this article, the authors review the microbiology, laboratory diagnosis, and epidemiology of LD.

Complete Genome Sequence of a Legionella longbeachae Serogroup 1 Strain Isolated from a Patient with Legionnaires' Disease

Legionella longbeachae serogroup 1, predominantly found in soil and composted plant material, causes the majority of cases of Legionnaires’ disease (LD) in New Zealand. Here, we report the complete genome sequence of an L. longbeachae serogroup 1 (sg1) isolate derived from a patient hospitalized with LD in Christchurch, New Zealand.

Comparison of the ImmuView and the BinaxNOW antigen tests in detection of Streptococcus pneumoniae and Legionella pneumophila in urine

The use of urinary antigen tests (UATs) may provide early etiology in pneumonia, and facilitates rapid and directed antibiotic treatment. In this study, we evaluated the novel lateral flow ImmuView Streptococcus pneumoniae and Legionella pneumophila UAT, which detects pneumococcal and L. pneumophila serogroup 1 antigens in a combined test. We compared the ImmuView UAT with the BinaxNOW S. pneumoniae UAT and the BinaxNOW L. pneumophila UAT in 147 patients with pneumococcal bacteremia (n = 48), non-pneumococcal non-Legionella bacteremia (n = 93) and Legionella infections in the lower airways (L. pneumophila, n = 5; L. bozemanii, n = 1). In three cases, the ImmuView test was invalid before and after boiling while the BinaxNOW tests were valid in all cases. In 144 cases, the three UATs demonstrated a very good inter-assay agreement for detection of pneumococcal antigen (κ = 0.86) and L. pneumophila antigen (κ = 1.00). The ImmuView and BinaxNOW S. pneumoniae tests had similar sensitivities (62% vs 60%; p = ns) in 48 cases with pneumococcal bacteremia and both tests had specificities of 97% in 96 cases with non-pneumococcal infections. Furthermore, the ImmuView and BinaxNOW L. pneumophila tests were positive for Legionella antigen in five patients with confirmed L. pneumophila serogroup 1 infections, and negative in all non-L. pneumophila cases. The ImmuView and BinaxNOW tests performed similarly when evaluated on urine samples from bacteremic and non-bacteremic patients with identified etiology.

Laboratory diagnosis of pneumonia in the molecular age

Pneumonia remains a worldwide health problem with a high rate of morbidity and mortality. Identification of microbial pathogens which cause pneumonia is an important area for optimum clinical management of pneumonia patients and is a big challenge for conventional microbiological methods. The development and implementation of molecular diagnostic tests for pneumonia has been a major advance in the microbiological diagnosis of respiratory pathogens in recent years. However, with new knowledge regarding the microbiome, together with the recognition that the lungs are a dynamic microbiological ecosystem, our current concept of pneumonia is not totally realistic as this new concept of pneumonia involves a dysbiosis or alteration of the lung microbiome. A new challenge for microbiologists and clinicians has therefore arisen. There is much to learn regarding the information provided by this new diagnostic technology, which will lead to improvements in the time to antibiotic therapy, targeted antibiotic selection and more effective de-escalation and improved stewardship for pneumonia patients. This article provides an overview of current methods of laboratory diagnosis of pneumonia in the molecular age.

Evaluation and Comparison of Multiple Test Methods, Including Real-time PCR, for Legionella Detection in Clinical Specimens

Legionella is a Gram-negative bacterium that can cause Pontiac fever, a mild upper respiratory infection and Legionnaire’s disease, a more severe illness. We aimed to compare the performance of urine antigen, culture, and polymerase chain reaction (PCR) test methods and to determine if sputum is an acceptable alternative to the use of more invasive bronchoalveolar lavage (BAL). Data for this study included specimens tested for Legionella at Public Health Ontario Laboratories from 1st January, 2010 to 30th April, 2014, as part of routine clinical testing. We found sensitivity of urinary antigen test (UAT) compared to culture to be 87%, specificity 94.7%, positive predictive value (PPV) 63.8%, and negative predictive value (NPV) 98.5%. Sensitivity of UAT compared to PCR was 74.7%, specificity 98.3%, PPV 77.7%, and NPV 98.1%. Out of 146 patients who had a Legionella-positive result by PCR, only 66 (45.2%) also had a positive result by culture. Sensitivity for culture was the same using either sputum or BAL (13.6%); sensitivity for PCR was 10.3% for sputum and 12.8% for BAL. Both sputum and BAL yield similar results regardless testing methods (Fisher Exact p-values = 1.0, for each test). In summary, all test methods have inherent weaknesses in identifying Legionella; therefore, more than one testing method should be used. Obtaining a single specimen type from patients with pneumonia limits the ability to diagnose Legionella, particularly when urine is the specimen type submitted. Given ease of collection and similar sensitivity to BAL, clinicians are encouraged to submit sputum in addition to urine when BAL submission is not practical from patients being tested for Legionella.

Prospective evaluation of RT-PCR on sputum versus culture, urinary antigens and serology for Legionnaire's disease diagnosis

OBJECTIVES

Legionnaires' disease (LD) is a severe disease associated with community and hospital-acquired pneumonia, frequently under diagnosed. The main aim of our study was to determine the value of PCR for the diagnosis of LD in routine clinical practice.

METHODS

In a prospective study, from March 2007 to April 2010, the value of PCR on non-invasive respiratory specimens (NIRS) was compared to those of the other available tools for LD diagnosis in patients hospitalized for pneumonia.

RESULTS

Among 254 consecutive cases of pneumonia included, 24 cases were LD (19 confirmed and 5 probable) representing the first documented microbiological etiology. Molecular diagnosis of LD was performed on NIRS by using 16S rRNA PCR, and secondarily mip PCR, with no discrepant results between the 2 methods: it was found positive in 14 cases and led to identify 2 supplementary probable cases of LD. Based on clinical and at least 2 positive LD tests, PCR yielded a better diagnostic value than antigen urinary test (12 vs 10 cases).

CONCLUSION

These results revealed that molecular diagnosis of LD on NIRS is reliable and may contribute to better identify cases of LD.

Community-acquired pneumonia related to intracellular pathogens

Community-acquired pneumonia (CAP) is associated with high rates of morbidity and mortality worldwide; the annual incidence of CAP among adults in Europe has ranged from 1.5 to 1.7 per 1000 population. Intracellular bacteria are common causes of CAP. However, there is considerable variation in the reported incidence between countries and change over time. The intracellular pathogens that are well established as causes of pneumonia are Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Chlamydophila psittaci, and Coxiella burnetii. Since it is known that antibiotic treatment for severe CAP is empiric and includes coverage of typical and atypical pathogens, microbiological diagnosis bears an important relationship to prognosis of pneumonia. Factors such as adequacy of initial antibiotic or early de-escalation of therapy are important variables associated with outcomes, especially in severe cases. Intracellular pathogens sometimes appear to cause more severe disease with respiratory failure and multisystem dysfunction associated with fatal outcomes. The clinical relevance of intracellular pathogens in severe CAP has not been specifically investigated. We review the prevalence, general characteristics, and outcomes of severe CAP cases caused by intracellular pathogens.

Legionnaires' disease caused by Legionella longbeachae: Clinical features and outcomes of 107 cases from an endemic area

BACKGROUND AND OBJECTIVE

Legionella longbeachae is a predominant cause of Legionnaires' disease in some parts of the world, particularly in Australasia. Clinical reports of L. longbeachae infection are limited to case reports or small case series, and culture-confirmed cases.

METHODS

We reviewed the clinical characteristics and outcomes of L. longbeachae pneumonia in a large case series from Christchurch, New Zealand during a 4-year period when both PCR and cultures were used as routine diagnostic tools for Legionnaires' disease. Cases of Legionella pneumophila pneumonia were reviewed for comparison.

RESULTS

A total of 107 cases of L. longbeachae infection were identified by PCR and/or culture. The median age was 65 years (range 25-90 years), 63% were male, and most became unwell during spring or summer. Presenting clinical features were similar to those reported for community-acquired pneumonia, with headache, myalgia and diarrhoea being common. Elevated C-reactive protein, hyponatraemia and abnormal liver function tests were also common. History of productive cough, involvement of both lungs, and high bacterial load were independently associated with culture of Legionella from lower respiratory samples. One quarter required intensive care unit admission, and 5% died. Among patients given antimicrobial therapy before admission, those given agents without anti-Legionella activity were more likely to be admitted to the intensive care unit. Limited comparisons were made with the 19 L. pneumophila cases over the same time period.

CONCLUSION

Characteristics of L. longbeachae pneumonia are broadly similar to those reported for community-acquired pneumonia from a variety of other populations, except for the spring/summer seasonality.

How best to determine causative pathogens of pneumonia

The biggest recent development in pneumonia diagnostics has been the increased availability and use of nucleic acid detection assays, although this change has brought with it new challenges about the interpretation of positive results. Recognition of the existence of the lung microbiome has challenged the traditional views of pneumonia pathogenesis and may provide the opportunity for new diagnostic tools that are focused on more than just detection of specific known pathogens.

Simultaneous detection of Legionella species and L. anisa, L. bozemanii, L. longbeachae and L. micdadei using conserved primers and multiple probes in a multiplex real-time PCR assay

Legionnaires' disease is a severe respiratory disease that is estimated to cause between 8,000 and 18,000 hospitalizations each year, though the exact burden is unknown due to under-utilization of diagnostic testing. Although Legionella pneumophila is the most common species detected in clinical cases (80-90%), other species have also been reported to cause disease. However, little is known about Legionnaires' disease caused by these non-pneumophila species. We designed a multiplex real-time PCR assay for detection of all Legionella spp. and simultaneous specific identification of four clinically-relevant Legionella species, L. anisa, L. bozemanii, L. longbeachae, and L. micdadei, using 5'-hydrolysis probe real-time PCR. The analytical sensitivity for detection of nucleic acid from each target species was ≤50fg per reaction. We demonstrated the utility of this assay in spiked human sputum specimens. This assay could serve as a tool for understanding the scope and impact of non-pneumophila Legionella species in human disease.

How recent advances in molecular tests could impact the diagnosis of pneumonia

Molecular diagnostic tests have been the single major development in pneumonia diagnostics over recent years. Nucleic acid detection tests (NATs) have greatly improved the ability to detect respiratory viruses and bacterial pathogens that do not normally colonize the respiratory tract. In contrast, NATs do not yet have an established role for diagnosing pneumonia caused by bacteria that commonly colonize the nasopharynx due to difficulties discriminating between pathogens and coincidental carriage strains. New approaches are needed to distinguish infection from colonization, such as through use of quantitative methods and identification of discriminating cut-off levels. The recent realization that the lung microbiome exists has provided new insights into the pathogenesis of pneumonia involving the interaction between multiple microorganisms. New developments in molecular diagnostics must account for this new paradigm.

Legionellosis in Transplantation

Legionella species are emerging opportunistic pathogens in hematopoietic stem cell and solid organ transplant recipients, associated with significant morbidity and mortality. The clinical and radiological features of Legionella infections can mimic other opportunistic pathogens in these profoundly immunocompromised patients. Diagnosis in transplant patients is challenging as non-pneumophila Legionella infections, for which these patients are at risk, cannot be identified using the urinary antigen test. Changes in management of transplant recipients and changes in Legionella epidemiology suggest that the number of transplant patients potentially exposed to Legionella spp. may be on the rise. Yet, evidence-based, transplant-specific guidelines for managing and preventing Legionella infections are not currently available. In this article, we review the epidemiology, clinical features, diagnostic challenges, treatment options, and preventive strategies of Legionella infections in these high-risk patient populations.

Microbiological diagnosis and molecular typing of Legionella strains during an outbreak of legionellosis in Southern Germany

An explosive outbreak of Legionnaires' disease with 64 reported cases occurred in Ulm/Neu-Ulm in the South of Germany in December 2009/January 2010 caused by Legionella (L.) pneumophila serogroup 1, monoclonal (mAb) subtype Knoxville, sequence type (ST) 62. Here we present the clinical microbiological results from 51 patients who were diagnosed at the University hospital of Ulm, the results of the environmental investigations and of molecular typing of patients and environmental strains. All 50 patients from whom urine specimens were available were positive for L. pneumophila antigen when an enzyme-linked immunosorbent assay (EIA) was used following concentration of those urine samples that tested initially negative. The sensitivity of the BinaxNow rapid immunographic assay (ICA), after 15 min reading and after 60 min reading were 70% and 84%, respectively. Direct typing confirmed the monoclonal subtype Knoxville in 5 out of 8 concentrated urine samples. Real time PCR testing of respiratory tract specimens for L. pneumophila was positive in 15 out of 25 (60%) patients. Direct nested sequence based typing (nSBT) in some of these samples allowed partial confirmation of ST62. L. pneumophila serogroup 1, monoclonal subtype Knoxville ST62, defined as the epidemic strain was isolated from 8 out of 31 outbreak patients (26%) and from one cooling tower confirming it as the most likely source of the outbreak. While rapid detection of Legionella antigenuria was crucial for the recognition and management of the outbreak, culture and molecular typing of the strains from patients and environmental specimens was the clue for the rapid identification of the source of infection.

Legionnaires' disease

Since first identified in early 1977, bacteria of the genus Legionella are recognised as a common cause of community-acquired pneumonia and a rare cause of hospital-acquired pneumonia. Legionella bacteria multisystem manifestations mainly affect susceptible patients as a result of age, underlying debilitating conditions, or immunosuppression. Water is the major natural reservoir for Legionella, and the pathogen is found in many different natural and artificial aquatic environments such as cooling towers or water systems in buildings, including hospitals. The term given to the severe pneumonia and systemic infection caused by Legionella bacteria is Legionnaires' disease. Over time, the prevalence of legionellosis or Legionnaires' disease has risen, which might indicate a greater awareness and reporting of the disease. Advances in microbiology have led to a better understanding of the ecological niches and pathogenesis of the condition. Legionnaires' disease is not always suspected because of its non-specific symptoms, and the diagnostic tests routinely available do not offer the desired sensitivity. However, effective antibiotics are available. Disease notification systems provide the basis for initiating investigations and limiting the scale and recurrence of outbreaks. This report reviews our current understanding of this disease.

Combined use of real-time PCR and nested sequence-based typing in survey of human Legionella infection

Legionnaires' disease (LD) is a globally distributed systemic infectious disease. The burden of LD in many regions is still unclear, especially in Asian countries including China. A survey of Legionella infection using real-time PCR and nested sequence-based typing (SBT) was performed in two hospitals in Shanghai, China. A total of 265 bronchoalveolar lavage fluid (BALF) specimens were collected from hospital A between January 2012 and December 2013, and 359 sputum specimens were collected from hospital B throughout 2012. A total of 71 specimens were positive for Legionella according to real-time PCR focusing on the 5S rRNA gene. Seventy of these specimens were identified as Legionella pneumophila as a result of real-time PCR amplification of the dotA gene. Results of nested SBT revealed high genetic polymorphism in these L. pneumophila and ST1 was the predominant sequence type. These data revealed that the burden of LD in China is much greater than that recognized previously, and real-time PCR may be a suitable monitoring technology for LD in large sample surveys in regions lacking the economic and technical resources to perform other methods, such as urinary antigen tests and culture methods.

Comparison of Legionella longbeachae and Legionella pneumophila cases in Scotland; implications for diagnosis, treatment and public health response

The reported incidence of Legionnaires' disease caused by Legionella longbeachae has increased since 2008 in Scotland. While microbiological and epidemiological studies have identified exposure to growing media as a risk factor for infection, little is known about the differences regarding disease risk factors, clinical features and outcomes of infection with L. longbeachae when compared with L. pneumophila. A nested case-case study was performed comparing 12 L. longbeachae cases with 25 confirmed L. pneumophila cases. Fewer L. longbeachae infected patients reported being smokers [27% (95% CI 2-52%) vs. 68% (95% CI 50-86%), P = 0.034] but more L. longbeachae patients experienced breathlessness [67% (95% CI 40-94%) vs. 28% (95% CI 10-46%), P = 0.036]. Significantly more L. longbeachae-infected patients received treatment in intensive care [50% (95% CI 22-78%) vs. 12% (95% CI 0-25%), P = 0.036]. However, the differences in diagnostic methods between the two groups may have led to only the most severe cases of L. longbeachae being captured by the surveillance system. No differences were observed in any of the other pre-hospital symptoms assessed. Our results highlight the similarity of Legionnaires' disease caused by L. pneumophila and L. longbeachae, and reinforce the importance of diagnostic tools other than the urinary antigen assays for the detection of non-L. pneumophila species. Unfortunately, cases of community-acquired pneumonia caused by Legionella species will continue to be underdiagnosed unless routine testing criteria changes.

Molecular diagnosis of Legionella infections--Clinical utility of front-line screening as part of a pneumonia diagnostic algorithm

OBJECTIVES

Urinary antigen testing for Legionella pneumophila serogroup 1 is the leading rapid diagnostic test for Legionnaires' Disease (LD); however other Legionella species and serogroups can also cause LD. The aim was to determine the utility of front-line L. pneumophila and Legionella species PCR in a severe respiratory infection algorithm.

METHODS

L. pneumophila and Legionella species duplex real-time PCR was carried out on 1944 specimens from hospitalised patients over a 4 year period in Edinburgh, UK.

RESULTS

L. pneumophila was detected by PCR in 49 (2.7%) specimens from 36 patients. During a LD outbreak, combined L. pneumophila respiratory PCR and urinary antigen testing had optimal sensitivity and specificity (92.6% and 98.3% respectively) for the detection of confirmed cases. Legionella species was detected by PCR in 16 (0.9%) specimens from 10 patients. The 5 confirmed and 1 probable cases of Legionella longbeachae LD were both PCR and antibody positive.

CONCLUSIONS

Front-line L. pneumophila and Legionella species PCR is a valuable addition to urinary antigen testing as part of a well-defined algorithm. Cases of LD due to L. longbeachae might be considered laboratory-confirmed when there is a positive Legionella species PCR result and detection of L. longbeachae specific antibody response.

Compost and Legionella longbeachae: an emerging infection?

Human disease caused by Legionella species is dominated by Legionella pneumophila, the main causative agent in cases of Legionnaires’ disease. However, other species are known to cause infection, for example, Legionella longbeachae causes an equivalent number of cases of disease as L. pneumophila in Australia and New Zealand. Infection with L. longbeachae is commonly associated with exposure to composts and potting soils, and cases of infection with this organism have been increasing in Europe over the past ten years. The increase in incidence may be linked to factors such as increased awareness of clinical presentation, or due to changing formulation of growing media, although it should be noted that the presence of Legionella species in growing media does not correlate with the number of cases currently seen. This is likely due to the variables associated with infection, for example, host factors such as smoking or underlying health conditions, or difference in growing media storage or climate, especially warm humid conditions, which may affect survival and growth of these organisms in the growing media environment. There are numerous unknowns in this area and collaboration between growing media manufacturers and researchers, as well as more awareness among diagnosing clinicians, laboratory staff and the general public is necessary to reduce risk. More research is needed before definitive conclusions can be drawn: L. pneumophila research currently dominates the field and it is likely that the overreliance on diagnostic techniques such as the urinary antigen test, which is specific for L. pneumophila Sg 1, is detrimental to the diagnosis of L. longbeachae infection.

Severe Neonatal Legionella Pneumonia: Full Recovery After Extracorporeal Life Support

Legionella pneumophila is responsible for hospital or community-acquired pneumonia. Neonatal legionellosis is associated with rapidly severe clinical course and high mortality rates. We describe a case of hospital-acquired Legionella pneumonia in a newborn with undiagnosed tracheoesophageal fistula and acute respiratory failure requiring venovenous extracorporeal membrane oxygenation support before fistula repair. Standardized multiplex polymerase chain reaction assay allowed early diagnosis. Extracorporeal life support associated with appropriate antibiotic therapy, surfactant, and steroid therapy was effective in achieving complete recovery. This is the first report of successful neonatal extracorporeal life support for respiratory failure secondary to L pneumophila.

Utility of PCR, Culture, and Antigen Detection Methods for Diagnosis of Legionellosis

The goal of this retrospective study was to evaluate the performance of different diagnostic tests for Legionnaires' disease in a clinical setting where Legionella pneumophila PCR had been introduced. Electronic medical records at the Cleveland Clinic were searched for Legionella urinary antigen (UAG), culture, and PCR tests ordered from March 2010 through December 2013. For cases where two or more test methods were performed and at least one was positive, the medical record was reviewed for relevant clinical and epidemiologic factors. Excluding repeat testing on a given patient, 19,912 tests were ordered (12,569 UAG, 3,747 cultures, and 3,596 PCR) with 378 positive results. The positivity rate for each method was 0.4% for culture, 0.8% for PCR, and 2.7% for UAG. For 37 patients, at least two test methods were performed with at least one positive result: 10 (27%) cases were positive by all three methods, 16 (43%) were positive by two methods, and 11 (30%) were positive by one method only. For the 32 patients with medical records available, clinical presentation was consistent with proven or probable Legionella infection in 84% of the cases. For those cases, the sensitivities of culture, PCR, and UAG were 50%, 92%, and 96%, respectively. The specificities were 100% for culture and 99.9% for PCR and UAG.