Complex clinical and microbiological effects on Legionnaires' disease outcone; A retrospective cohort study

Epidemiological Analysis of Legionella Pneumonia in Japan: A National Inpatient Database Study

BACKGROUND

Legionella pneumonia, a severe form of pneumonia, is caused by Legionella bacteria. The epidemiology of Legionnaires' disease in Japan, including seasonal trends, risk factors for severe disease, and fatality rates, is unclear. This study examined the epidemiology of Legionella pneumonia in Japan.

METHODS

This retrospective cohort study included data of adult patients hospitalized for Legionella pneumonia (identified using the International Classification of Diseases, 10th revision code, A481) in the Japanese Diagnosis Procedure Combination inpatient database, from April 2011 to March 2021. We performed multivariable logistic regression analysis to explore the prognostic factors of in-hospital mortality.

RESULTS

Of 7,370 enrolled hospitalized patients from 1,140 hospitals (male, 84.4%; aged >50 years, 87.9%), 469 (6.4%) died during hospitalization. The number of hospitalized patients increased yearly, from 658 in 2016 to 975 in 2020. Multivariable logistic regression analysis revealed that higher in-hospital mortality was associated with older age, male sex, lower body mass index, worsened level of consciousness, comorbidities (congestive heart failure, chronic renal diseases, and metastasis), hospitalization from November to May, and ambulance use. However, lower in-hospital mortality was associated with comorbidity (liver diseases), hospitalization after 2013, and hospitalization in hospitals with higher case volume.

CONCLUSION

The characterized epidemiology of Legionella pneumonia in Japan revealed a high mortality rate of 6.4%. To the best of our knowledge, this is the first study to demonstrate a higher mortality rate in winter and in patients with congestive heart failure and metastasis. Further research is needed to understand the complex interplay between the prognostic factors of Legionella pneumonia.

Rapid Colorimetric Quantita2tive Portable Platform for Detection of Brucella melitensis Based on a Fluorescence Resonance Energy Transfer Assay and Nanomagnetic Particles

Brucellosis is a bacterial zoonotic disease that requires major attention for both health and financial facilities in many parts of the world including the Mediterranean and the Middle East. The existing gold standard diagnosis relies on the culturing technique, which is costly and time-consuming with a duration of up to 45 days. The Brucella protease biosensor represents a new detection approach that will lead to low-cost point-of-care devices for sensitive Brucella detection. In addition, the described diagnostic device is portable and simple to operate by a nurse or non-skilled clinician making it appropriate for the low-resource setting. In this study, we rely on the total extracellular protease proteolytic activity on specific peptide sequences identified using the FRET assay by high-throughput screening from the library of peptide (96 short peptides such as dipeptides and tripeptides) substrates for Brucella melitensis (B. melitensis). The B. melitensis-specific protease substrate was utilized in the development of the paper-based colorimetric assay. Two specific and highly active dipeptide substrates were identified (FITC-Ahx-K-r-K-Ahx-DABCYL and FITC-Ahx-R-r-K-Ahx-DABCYL). The peptide-magnetic bead nanoprobe sensors developed based on these substrates were able to detect the Brucella with LOD as low as 1.5 × 102 and 1.5 × 103 CFU/mL using K-r dipeptide and R-r dipeptide substrates, respectively, as the recognition element. The samples were tested using this sensor in few minutes. Cross-reactivity studies confirmed that the other proteases extracted from closely related pathogens have no significant effect on the sensor. To the best of our knowledge, this assay is the first assay that can be used with low-cost, rapid, direct, and visual detection of B. melitensis.

An Epidemiological Study on Legionnaires' Disease in Gyeonggi Province, Korea: Occurrence, Infection Routes, and Risk Factors for Mortality (2016-2022)

Background and Objectives: Legionnaires' disease (LD) is an acute respiratory disease with increasing annual numbers of reported domestic and global cases. This study aimed to establish foundational data for the prevention and control of LD by investigating the occurrence and infection routes of reported and suspected cases of LD in Gyeonggi Province, Korea, from January 2016 to December 2022, and by and analyzing the risk factors for death. Materials and Methods: A sex-and-age standardization was performed on LD patients and suspected cases reported in Gyeonggi Province. The monthly average number of confirmed cases was visualized using graphs, and a survival analysis was performed using Kaplan-Meier survival curves. The mortality risk ratio was estimated using the Cox proportional hazards model. Results: The incidence of LD in Gyeonggi Province mirrored the national trend, peaking in July with the highest number of confirmed and suspected cases. While there was no significant difference in survival rates by age, the survival rate was higher for suspected cases when analyzed separately. Comparing the death ratio by infection route, nosocomial infections showed the highest death ratio, and intensive care unit (ICU) admission and the presence of coinfections were significantly correlated with mortality. Factors such as nosocomial infection, admission within 1 to 3 days following diagnosis, and the development of complications were factors contributing to a higher risk of death. Conclusions: The general characteristics of patients with LD were similar to those suggested by previous studies. The proportion of community-acquired infections was lower than in previous studies, but the length of hospital stay was similar for survivors and the deceased, and the mortality rate within 30 days after diagnosis was higher for nosocomial infections. In conclusion, nosocomial infection, a period of up to 3 days from admission to diagnosis, and complications were significantly related to the mortality rate of LD.

Hyper-inflammatory profile and immunoparalysis in patients with severe Legionnaires' disease

Introduction

Severe Legionnaires' disease (LD) can lead to multi-organ failure or death in 10%-30% of patients. Although hyper-inflammation and immunoparalysis are well described in sepsis and are associated with high disease severity, little is known about the immune response in LD. This study aimed to evaluate the immune status of patients with LD and its association with disease severity.

Methods

A total of 92 hospitalized LD patients were included; 19 plasmatic cytokines and pulmonary Legionella DNA load were measured in 84 patients on the day of inclusion (day 0, D0). Immune functional assays (IFAs) were performed from whole blood samples collected at D2 and stimulated with concanavalin A [conA, n = 19 patients and n = 21 healthy volunteers (HV)] or lipopolysaccharide (LPS, n = 14 patients and n = 9 HV). A total of 19 cytokines (conA stimulation) and TNF-α (LPS stimulation) were quantified from the supernatants. The Sequential Organ Failure Assessment (SOFA) severity score was recorded at D0 and the mechanical ventilation (MV) status was recorded at D0 and D8.

Results

Among the 84 patients, a higher secretion of plasmatic MCP-1, MIP1-β, IL-6, IL-8, IFN-γ, TNF-α, and IL-17 was observed in the patients with D0 and D8 MV. Multiparametric analysis showed that these seven cytokines were positively associated with the SOFA score. Upon conA stimulation, LD patients had a lower secretion capacity for 16 of the 19 quantified cytokines and a higher release of IL-18 and MCP-1 compared to HV. IL-18 secretion was higher in D0 and D8 MV patients. TNF-α secretion, measured after ex vivo LPS stimulation, was significantly reduced in LD patients and was associated with D8 MV status.

Discussion

The present findings describe a hyper-inflammatory phase at the initial phase of Legionella pneumonia that is more pronounced in patients with severe LD. These patients also present an immunoparalysis for a large number of cytokines, except IL-18 whose secretion is increased. An assessment of the immune response may be relevant to identify patients eligible for future innovative host-directed therapies.

Antimicrobial susceptibility profiles and tentative epidemiological cutoff values of Legionella pneumophila from environmental water and soil sources in China

Legionnaires’ disease (LD), caused by Legionella, including the most prevalent Legionella pneumophila, has been treated primarily with antibiotics. Environmental water and soil are the reservoirs for L. pneumophila. Studying antimicrobial susceptibility using a large number of isolates from various environmental sources and regions could provide an unbiased result. In the present study, antimicrobial susceptibility of 1464 environmental L. pneumophila isolates that were derived from various environmental water and soil sources of 12 cities in China to rifampin (RIF), erythromycin (ERY), clarithromycin (CLA), azithromycin (AZI), ciprofloxacin (CIP), moxifloxacin (MOX), levofloxacin (LEV), and doxycycline (DOX) was investigated, and minimum inhibitory concentration (MIC) data were obtained. We show that regarding macrolides, ERY was least active (MIC₉₀ = 0.5 mg/L), while CLA was most active (MIC₉₀ = 0.063 mg/L). A total of three fluoroquinolones have similar MICs on L. pneumophila. Among these antimicrobials, RIF was the most active agent, while DOX was the most inactive one. We observed different susceptibility profiles between serogroup 1 (sg1) and sg2-15 or between water and soil isolates from different regions. The ECOFFs were ERY and AZI (0.5 mg/L), RIF (0.002 mg/L), CIP, CLA and MOX (0.125 mg/L), LEV (0.063 mg/), and DOX (32 mg/L). Overall, two fluoroquinolone-resistant environmental isolates (0.14%) were first documented based on the wild-type MIC distribution. Not all azithromycin-resistant isolates (44/46, 95.65%) harbored the lpeAB efflux pump. The MICs of the ERY and CLA on the lpeAB + isolates were not elevated. These results suggested that the lpeAB efflux pump might be only responsible for AZI resistance, and undiscovered AZI-specific resistant mechanisms exist in L. pneumophila. Based on the big MIC data obtained in the present study, the same defense strategies, particularly against both CLA and RIF, may exist in L. pneumophila. The results determined in our study will guide further research on antimicrobial resistance mechanisms of L. pneumophila and could be used as a reference for setting clinical breakpoints and discovering antimicrobial-resistant isolates in the clinic, contributing to the antibiotic choice in the treatment of LD.

A risk model to identify Legionella among patients admitted with community-acquired pneumonia: A retrospective cohort study

BACKGROUND

Guidelines recommend testing hospitalized patients with community-acquired pneumonia (CAP) for Legionella pneumophila only if the infection is severe or risk factors are present. There are no validated models for predicting Legionella.

OBJECTIVE

To derive and externally validate a model to predict a positive Legionella test.

DESIGN, SETTING AND PARTICIPANTS

Diagnostic study of adult inpatients with pneumonia using data from 177 US hospitals in the Premier Healthcare Database (training and hold-out validation sets) and 12 Cleveland Clinic Health System (CCHS) hospitals (external validation set). We used multiple logistic regression to predict positive Legionella tests in the training set, and evaluated performance in both validation sets.

MAIN OUTCOME AND MEASURES

The outcome was a positive Legionella test. Potential predictors included demographics and co-morbidities, disease severity indicators, season, region, and presence of a local outbreak.

RESULTS

Of 166,689 patients hospitalized for pneumonia, 43,070 were tested for Legionella and 642 (1.5%) tested positive. The strongest predictors of a positive test were a local outbreak (odds ratio [OR], 3.4), June-October occurrence (OR, 3.4), hyponatremia (OR, 3.3), smoking (OR, 2.4), and diarrhea (OR, 2.0); prior admission within 6 months (OR, 0.27) and chronic pulmonary disease (OR, 0.49) were associated with a negative test. Model c-statistics were 0.79 in the Premier and 0.77 in the CCHS validation samples. High-risk patients were only slightly more likely to have been tested than lower-risk patients. Compared to actual practice, the model-based testing strategy detected twice as many cases.

CONCLUSIONS

Although Legionella is an uncommon cause of pneumonia, patient characteristics can identify individuals at high risk, allowing for more efficient testing.

Urinary Antigen Testing for Respiratory Infections: Current Perspectives on Utility and Limitations

Pneumonia is a leading cause of hospitalization and death due to infection worldwide. Streptococcus pneumoniae and Legionella pneumophila remain among the most commonly identified bacterial pathogens. Unfortunately, more than half of all pneumonia cases today lack an etiologic diagnosis due to limitations in traditional microbiological methods like blood and sputum cultures, which are affected by poor sample collection, prior antibiotic administration, and delayed processing. Urinary antigen tests (UATs) for S. pneumoniae and L. pneumophila have emerged as powerful tools for improving the diagnosis of bacterial respiratory infections, enabling physicians to administer early directed therapy and improve antimicrobial stewardship. UATs are simple, rapid, and non-invasive diagnostic tests with high specificity (>90%) and moderate sensitivity (<80%). The potential impact of urinary antigen testing is especially significant for respiratory infections caused by Legionella. While all recommended community-acquired pneumonia (CAP) therapies are adequate for treating pneumococcal pneumonia, only certain antibiotics are effective against Legionella. Delayed therapy for Legionella is associated with worse clinical outcomes, which underscores the importance of rapid diagnostic methods like UATs. Despite their potential impact, current American Thoracic Society and Infectious Diseases Society of America (ATS/IDSA) guidelines argue against the routine use of urinary antigen testing for S. pneumoniae and L. pneumophila, except in patients with severe CAP and those with epidemiological risk factors for Legionella. Further research is necessary to evaluate the impact of early targeted treatment due to positive UAT results, as well as optimal strategies for UAT utilization. The purpose of this review is to summarize the UATs available for bacterial respiratory infections, describe current guidelines on their usage, and assess their impact on clinical outcomes and targeted therapy.

Legionella Pneumonia in the ICU: A Tertiary Care Center Experience Over 10 Years

OBJECTIVES:

Few studies have reported the complications and outcomes of patients with Legionella pneumonia requiring ICU admission. The objective of our study is to report the clinical course, complications, and 30-day mortality of patients with Legionella pneumonia admitted to the critical care units at our medical center over a 10-year period.

DESIGN:

Retrospective observational study.

SETTING:

Tertiary care teaching hospital.

PATIENTS:

All adult (≥ 18 yr old) patients with Legionella pneumonia admitted to the ICUs from January 1, 2010, to December 31, 2019.

INTERVENTIONS:

None.

MEASUREMENTS AND MAIN RESULTS:

A total of 88 patients with Legionella pneumonia were admitted to ICUs over the 10-year period. The majority of infections (n = 80; 90.9%) were community acquired. The median (interquartile range) age of patients was 60 years (51.5–71.0 yr); 58 (66%) were male, and 41 (46.6%) identified their race as Black. The median (interquartile range) Sequential Organ Failure Assessment score at ICU admission was 6 (3–9). The distribution of infections showed seasonal dominance with most cases (86%) occurring in the summer to early fall (May to October). Invasive mechanical ventilation was required in 62 patients (70.5%), septic shock developed in 57 patients (64.8%), and acute respiratory distress syndrome developed in 42 patients (47.7%). A majority of patients developed acute kidney injury (n = 69; 78.4%), with 15 (21.7%) receiving only intermittent hemodialysis and 15 (21.7%) requiring continuous renal replacement therapy. Ten patients required venovenous extracorporeal membrane oxygenation support; eight (80%) survived and were successfully decannulated. Overall 30-day mortality was 26.1% (n = 23). Advanced age, higher Sequential Organ Failure Assessment score at admission, and not receiving Legionella-specific antimicrobial therapy within 24 hours of hospital admission were predictors of 30-day mortality.

CONCLUSIONS:

Patients with Legionella pneumonia may require ICU admission and major organ support. Legionella-targeted antibiotics should be included in the empiric regimen for any patient with severe pneumonia. Outcomes of extracorporeal membrane oxygenation therapy in this population are encouraging.

Community-acquired versus nosocomial Legionella pneumonia: factors associated with Legionella-related mortality

Over the past decade, changes in the diagnosis and management of Legionella pneumonia occurred and risk factors for severe infection and increased mortality were identified. Previous reports found that nosocomial infection is associated with higher mortality while others showed no differences. We aimed to evaluate the differences in the clinical course and mortality rates between hospital-acquired pneumonia (HAP) and community-acquired pneumonia (CAP) caused by Legionella pneumophila. A retrospective cohort study of patients admitted due to Legionella pneumonia between January 2012 through November 2019 was conducted in a tertiary referral center (Rambam Health Care Campus, Haifa, Israel). The primary outcome was 30-day Legionella pneumonia-related mortality. A multivariable logistic regression was performed to determine whether a nosocomial infection is an independent predictor of mortality. One hundred nine patients were included. Seventy (64.2%) had CAP and 39 (35.8%) had HAP. The groups were comparable regarding age, gender, and comorbidities. Time to diagnosis was longer and the number of patients receiving initial empiric anti-Legionella spp. treatment was smaller in the HAP group (8 days [IQR 5.5-12.5] vs. 5 days [IQR 3-8], p < 0.001 and 65.5% vs. 78.6%, p = 0.003, respectively). Patients with HAP had higher 30-day mortality, 41% vs. 18.6%, p = 0.02. In a multivariable logistic regression model, only pneumonia severity index and nosocomial source were independently associated with increased mortality. HAP caused by Legionella spp. is independently associated with increased mortality when compared to CAP caused by the same pathogen. The possible reasons for this increased mortality include late diagnosis and delayed initiation of appropriate treatment.

Simple and rapid peptide nanoprobe biosensor for the detection of Legionellaceae

This study demonstrates the development of a sensitive, specific, and quantitative peptide-based nanoprobe prototype assay for the detection of Legionellaceae in a simple way and in a short time. In this work, proteases present in the culture supernatants of Legionella spp. were used as a biomarker. Fluorogenic peptide substrates, specific to Legionella strains culture supernatant proteases, were identified. Peptidases produced a significant increase in the fluorescence intensity following the cleavage of the dipeptide fluorogenic substrates. The specific substrates were identified and coupled with carboxyl-terminated nano-magnetic particles (NMPs). On the other hand, the C-terminal was conjugated with the cysteine residue to covalently integrate with a gold sensing platform via the Au-S linkage. Four different sensors were fabricated from the four specific substrates, which were treated with the protesase of six different species of Legionella. In the presence of specific protease, the peptide sequence is digested and the magnetic nanobeads moved out of the gold surface, resulting in the apparence of gold color. One of the nanoprobes sensitivity detects as low as 60 CFU mL^-1 of Legionella anisa, Legionella micdadei, and Fluoribacter dumoffii. The cross-reactivity of the sensors was tested using other closely associated bacterial species and no significant cross-reactivity of the sensors was found. It is envisaged that this assay could be useful for screening purposes or might be supportive for the fast and easy detection of Legionella protease activity for water monitoring purposes.

Trends in the incidence and mortality of legionellosis in Japan: a nationwide observational study, 1999-2017

This study examined temporal trend, seasonality, and geographical variations of legionellosis incidence and mortality in Japan. This nationwide observational study used the Japanese Vital Statistics and Infectious Diseases Weekly Report (1999-2017) data to calculate legionellosis crude and age-adjusted incidence and mortality rates per 100,000 population by age and sex. Incidence was compared among the 4 seasons and regional incidence among 47 prefectures. Of 13,613 (11,194 men) people with legionellosis in Japan, 725 (569 men) were fatal. Increasing incidence trend occurred from 0.0004 (1999) to 1.37 (2017) per 100,000 population. People aged ≥ 70 years accounted for 43.1% overall; men's age-adjusted incidence rate was consistently approximately five times higher than for women. Significantly higher incidence occurred in summer than in winter (p = 0.013). Geographically, highest incidence (≥ 2.0 per 100,000 population) occurred in Hokuriku District, with increasing trends in Hokkaido and middle-part of Japan. Estimated fatality rates decreased consistently at 5.9% (95% confidence interval: - 8.1, - 3.5) annually, from 1999 to 2017, with no trend change point. Increasing legionellosis incidence occurred in Japan during 1999-2017, with declining estimated fatality rates. In this aging society and warming world, disease clinical burden may further deteriorate in future due to increasing incidence trends.

A Hospital-based Study on the Local Epidemiology of Pneumonia Including the Contribution of Legionella Pneumonia

Background

In real-life practice, only 20% of hospitalised pneumonia cases have an identified etiology. The usage of Legionella urine antigen test (LUAT) in developed nations revolutionised case detection rates. Accordingly, our objectives were to study the microbiological etiology for hospitalised pneumonia patients and the diagnosis of Legionella pneumonia.

Methods

A prospective, observational single-centre study was conducted where all 504 cases that were consecutively admitted for pneumonia were enrolled. Blood and sputum samples obtained were used to identify pathogens using standard microbiological culture methods. The urine samples collected were tested using the Immunocatch^TMLegionella immunochromatographic (ICT) urine antigen test.

Results

A microbiological diagnosis was only achieved in 104 cases (20.6%) and a Gram-negative infection predominance was observed. Culture-positive cases required longer hospitalisation (8.46 days versus 5.53 days; P < 0.001) and the higher usage of antipseudomonal antibiotics (23.1% versus 8.3%; P < 0.001). Only 3 cases (0.6%) were diagnosed with Legionella pneumonia.

Conclusion

The local pathogen distribution is diverse compared to other regions. Culture-negative pneumonia is common and significantly differs from culture-positive pneumonia. Legionella pneumophila serotype 1 is not a common cause of pneumonia and LUAT did not help demystify the cause of culture-negative pneumonia.

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.

Antimicrobial strategy for severe community-acquired legionnaires' disease: a multicentre retrospective observational study

Background

Legionnaires' disease (LD) is an important cause of community-acquired pneumonia with high mortality rates in the most severe cases.

Objectives

To evaluate the effect of antimicrobial strategy on ICU mortality.

Methods

Retrospective, observational study including patients admitted to 10 ICUs for severe community-acquired LD over a 10 year period (2005-15) and receiving an active therapy within 48 h of admission . Patients were stratified according to the antibiotic strategy administered: (i) fluoroquinolone-based versus non-fluoroquinolone-based therapy; and (ii) monotherapy versus combination therapy. The primary endpoint was in-ICU mortality. A multivariable Cox model and propensity score analyses were used.

Results

Two hundred and eleven patients with severe LD were included. A fluoroquinolone-based and a combination therapy were administered to 159 (75%) and 123 (58%) patients, respectively. One hundred and forty-six patients (69%) developed acute respiratory distress syndrome and 54 (26%) died in the ICU. In-ICU mortality was lower in the fluoroquinolone-based than in the non-fluoroquinolone-based group (21% versus 39%, P  =   0.01), and in the combination therapy than in the monotherapy group (20% versus 34%, P  =   0.02). In multivariable analysis, a fluoroquinolone-based therapy, but not a combination therapy, was associated with a reduced risk of mortality [HR = 0.41, 95% CI 0.19-0.89; P  =   0.02].

Conclusions

Patients with severe LD receiving a fluoroquinolone-based antimicrobial regimen in the early course of management had a lower in-ICU mortality, which persisted after adjusting for significant covariates.