Accuracy of diagnostic tests for Legionnaires' disease: a systematic review

Venovenous extracorporeal membrane oxygenation after cardiac arrest for acute respiratory distress syndrome caused by Legionella: a case report

BACKGROUND

Legionella remains underdiagnosed in the intensive care unit and can progress to acute respiratory distress syndrome (ARDS), multiorgan failure and death. In severe cases, venovenous extracorporeal membrane oxygenation (VV-ECMO) allows time for resolution of disease with Legionella-targeted therapy. VV-ECMO outcomes for Legionella are favorable with reported survival greater than 70%. Rapid molecular polymerase chain reaction (PCR) testing of the lower respiratory tract aids in diagnosing Legionella with high sensitivity and specificity. We present a unique case of a patient with a positive COVID-19 test and ARDS who suffered a cardiac arrest. The patient was subsequently cannulated for VV-ECMO, and after lower respiratory tract PCR testing, Legionella was determined to be the cause. She was successfully treated and decannulated from VV-ECMO after eight days.

CASE PRESENTATION

A 53-year-old female presented with one week of dyspnea and a positive COVID-19 test. She was hypoxemic, hypotensive and had bilateral infiltrates on imaging. She received supplemental oxygen, intravenous fluids, vasopressors, broad spectrum antibiotics, and was transferred to a tertiary care center. She developed progressive hypoxemia and suffered a cardiac arrest, requiring ten minutes of CPR and endotracheal intubation to achieve return of spontaneous circulation. Despite mechanical ventilation and paralysis, she developed refractory hypoxemia and was cannulated for VV-ECMO. Dexamethasone and remdesivir were given for presumed COVID-19. Bronchoscopy with bronchoalveolar lavage (BAL) performed with PCR testing was positive for Legionella pneumophila and negative for COVID-19. Steroids and remdesivir were discontinued and she was treated with azithromycin. Her lung compliance improved, and she was decannulated after eight days on VV-ECMO. She was discharged home on hospital day 16 breathing room air and neurologically intact.

CONCLUSIONS

This case illustrates the utility of rapid PCR testing to diagnose Legionella in patients with respiratory failure and the early use of VV-ECMO in patients with refractory hypoxemia secondary to Legionella infection. Moreover, many patients encountered in the ICU may have prior COVID-19 immunity, and though a positive COVID-19 test may be present, further investigation with lower respiratory tract PCR testing may provide alternative diagnoses. Patients with ARDS should undergo Legionella-specific testing, and if Legionella is determined to be the causative organism, early VV-ECMO should be considered in patients with refractory hypoxemia given reported high survival rates.

Estimating the burden of illness caused by domestic waterborne Legionnaires' disease in Canada: 2015-2019

Legionellosis is a disease caused by the bacterium Legionella that most commonly presents as Legionnaires' disease (LD), a severe form of pneumonia. From 2015 to 2019, an average of 438 LD cases per year were reported in Canada. However, it is believed that the actual number of cases is much higher, since LD may be underdiagnosed and underreported. The purpose of this study was to develop an estimate of the true incidence of illnesses, hospitalizations, and deaths associated with LD in Canada. Values were derived using a stochastic model, based on Canadian surveillance data from 2015 to 2019, which were scaled up to account for underdiagnosis and underreporting. Overall, there were an estimated 1,113 (90% CrI: 737-1,730) illnesses, 1,008 (90% CrI: 271-2,244) hospitalizations, and 34 (90% CrI: 4-86) deaths due to domestically acquired waterborne LD annually in Canada from 2015 to 2019. It was further estimated that only 36% of illnesses and 39% of hospitalizations and deaths were captured in surveillance, and that 22% of illnesses were caused by Legionella serogroups and species other than Legionella pneumophila serogroup 1 (non-Lp1). This study highlights the true burden and areas for improvement in Canada's surveillance and detection of LD.

Evaluation of the BioFire® FilmArray® Pneumonia plus Panel for Detecting Bacterial Etiological Agents of Lower Respiratory Tract Infections in an Oncologic Hospital. Comparison with Conventional Culture Method

Conventional methods used to determine pneumonia pathogens are characterized by low sensitivity and long turnaround times. Introducing new tests with better parameters in patients at higher risk of infections is highly anticipated. The results of the conventional quantitative culture method (CM) in determining the bacterial etiology of pneumonia were compared with the results of the Pneumonia plus Panel test (PNP; BioFire® Diagnostics, USA) in 79 samples of bronchoalveolar lavage (BAL). Materials were collected from 79 patients with suspected pneumonia treated in an oncologic hospital due to solid tumors. Only 16/79 BAL samples (20.3%) were true positive (TP) for bacterial etiology in CM vs. 27/79 samples (34.2%) true positive in the PNP test. The total agreement between methods of interpreting the result (positive or negative) was 84.8%. The most prevalent pathogens in both methods were Staphylococcus aureus, followed by Escherichia coli, Pseudomonas aeruginosa, and Haemophilus influenzae. The PNP test identified several respiratory pathogens that were not grown in culture. The semiquantitative value reported by the PNP test was higher than that reported by culture. The PNP test vs. combined test (PNP test and CM methods) demonstrated positive predictive value (PPV) and negative predictive value (NPV) values of 100.0% and 98.1%, and the sensitivity and specificity were 96.4% and 100.0%. The PNP test is a good tool for determining the etiology of bacterial pneumonia and may support the care of an oncologic patient. However, further large-sample studies are needed to research in strictly defined groups of oncologic patients.

A meta-analysis of Legionella pneumophila contamination in hospital water systems

BACKGROUND

Legionella pneumophila is a common cause of community-acquired pneumonia. We aimed to determine the pooled rates of L pneumophila contamination in the water environment of the hospital.

METHODS

We searched PubMed, Embase, Web of Science, Chinese National Knowledge Infrastructure, WangFang and Science Direct, The Cochrane Library, and Science Finder, for relevant studies published until December 2022. Stata 16.0 software was used to determine pooled contamination rates, publication bias, and subgroup analysis.

RESULTS

Forty-eight eligible articles with a total of 23,640 samples of water were evaluated, and the prevalence of L pneumophila was 41.6%. The results of the subgroup analysis showed that the pollution rate of L pneumophila in hot water (47.6%) was higher than that in other water bodies. The rates of L pneumophila contamination were higher in developed countries (45.2%), culture methods (42.3%), published between 1985 and 2015 (42.9%), and studies with a sample size of less than 100 (53.0%).

CONCLUSIONS

L pneumophila contamination in medical institutions is still very serious and should be paid attention to, especially in developed countries and hot water tanks.

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.

Atypical Pathogens in Adult Community-Acquired Pneumonia and Implications for Empiric Antibiotic Treatment: A Narrative Review

Atypical pathogens are intracellular bacteria causing community-acquired pneumonia (CAP) in a significant minority of patients. Legionella spp., Chlamydia pneumoniae and psittaci, Mycoplasma pneumoniae, and Coxiella burnetii are commonly included in this category. M. pneumoniae is present in 5-8% of CAP, being the second most frequent pathogen after Streptococcus pneumoniae. Legionella pneumophila is found in 3-5% of inpatients. Chlamydia spp. and Coxiella burnetii are present in less than 1% of patients. Legionella longbeachae is relatively frequent in New Zealand and Australia and might also be present in other parts of the world. Uncertainty remains on the prevalence of atypical pathogens, due to limitations in diagnostic means and methodological issues in epidemiological studies. Despite differences between CAP caused by typical and atypical pathogens, the clinical presentation alone does not allow accurate discrimination. Hence, antibiotics active against atypical pathogens (macrolides, tetracyclines and fluoroquinolones) should be included in the empiric antibiotic treatment of all patients with severe CAP. For patients with milder disease, evidence is lacking and recommendations differ between guidelines. Use of clinical prediction rules to identify patients most likely to be infected with atypical pathogens, and strategies of narrowing the antibiotic spectrum according to initial microbiologic investigations, should be the focus of future investigations.

Diagnostic accuracy of urinary antigen tests for legionellosis: A systematic review and meta-analysis

BACKGROUND

Urinary antigen tests (UATs) have been used for the early detection of legionellosis and have demonstrated moderate sensitivity and high specificity. However, the most recent systematic review and meta-analysis published in 2009 evaluated the accuracy of UATs; since then, UAT accuracy may have changed owing to advances and developments in UAT technology and epidemiological changes in the frequency of Legionella species that cause legionellosis. Therefore, this systematic review and meta-analysis aimed to update the accuracy of UATs for legionellosis among patients with suspected pneumonia.

METHODS

Overall, 1326 studies were screened, 21 of which fulfilled the eligibility criteria for quality assessment and meta-analysis. Data from 5772 patients, including 1368 (23.7%) with the target condition (i.e., suspected legionellosis), were included in the analysis. The overall quality of the included studies, which was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool, was unclear.

RESULTS

The calculated pooled sensitivity and specificity were 0.79 (95% confidence interval [CI], 0.71-0.85) and 1.00 (95% CI, 0.99-1.00), respectively. Subpopulation analysis revealed that the accuracy of UATs for sensitivity and specificity for Legionella pneumophilia serogroup 1 was 0.86 (95% CI, 0.78-0.91) and 1.00 (95% CI, 0.99-1.00), respectively.

CONCLUSIONS

This study demonstrated that the sensitivity and specificity of UATs were moderate and high, respectively, which is comparable to the results reported in 2009. Therefore, UATs may be a useful method for the early detection of legionellosis caused by Legionella pneumophila serogroup 1.

CLINICAL TRIAL REGISTRATION

The review protocol was prospectively registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN000041080).

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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.

Legionella pneumophila in Patients with Pneumonia at a Referral Hospital, New Delhi, India, 2015-2020

Legionnaires' disease (LD) is an established cause of pneumonia, and the disease remains largely underdiagnosed. Even though LD has been reported from many parts of the world, only sporadic cases have been reported in India. During February 2015-January 2020, we enrolled 597 patients with radiographically confirmed pneumonia and tested respiratory secretions for Legionella spp. by using real-time PCR, and culture. A commercial urinary antigen test (UAT) was also used to detect the Legionella pneumophila (Lp) serogroup 1 antigen in urine. An LD case was defined as a patient with pneumonia and positive results for Legionella spp. infections determined by real-time PCR (from any respiratory specimen) or culture or UAT. Demographic data, risk factors, clinical, radiological, and outcome data of Lp-positive and Lp-negative patients were compared using logistic regression. Over the study period, 14 (2.3%) patients were positive for Legionella spp. infections by real-time PCR and UAT; eight (57%) were admitted to the intensive care unit, and four (28.6%) in-hospital deaths occurred. Bivariate analysis showed that renal disease, neurological conditions, confusion, leukocytosis, and requirement of oxygen support were more common in the Lp-positive group than in the Lp-negative group. However, multivariate analysis failed to confirm most of these differences; renal disease was the only independent variable remaining significant. All test methods have intrinsic limitations in identifying Legionella; therefore, more than one testing method should be used. Application of molecular assays including real-time PCR has great value because of its high sensitivity, specificity, and rapid diagnostic potency. Increased awareness and improved diagnostic testing could facilitate early detection of cases, pathogen-directed therapy, and improved outcomes for patients.

Performance of Legiolert Test vs. ISO 11731 to Confirm Legionella pneumophila Contamination in Potable Water Samples

Detection and enumeration of Legionella in water samples is of great importance for risk assessment analysis. The plate culture method is the gold standard, but has received several well-known criticisms, which have induced researchers to develop alternative methods. The purpose of this study was to compare Legionella counts obtained by the analysis of potable water samples through the plate culture method and through the IDEXX liquid culture Legiolert method. Legionella plate culture, according to ISO 11731:1998, was performed using 1 L of water. Legiolert was performed using both the 10 mL and 100 mL Legiolert protocols. Overall, 123 potable water samples were analyzed. Thirty-seven (30%) of them, positive for L. pneumophila, serogroups 1 or 2–14 by plate culture, were used for comparison with the Legiolert results. The Legiolert 10 mL test detected 34 positive samples (27.6%) and the Legiolert 100 mL test detected 37 positive samples, 27.6% and 30% respectively, out of the total samples analyzed. No significant difference was found between either the Legiolert 10 mL and Legiolert 100 mL vs. the plate culture (p = 0.9 and p = 0.3, respectively) or between the Legiolert 10 mL and Legiolert 100 mL tests (p = 0.83). This study confirms the reliability of the IDEXX Legiolert test for Legionella pneumophila detection and enumeration, as already shown in similar studies. Like the plate culture method, the Legiolert assay is also suitable for obtaining isolates for typing purposes, relevant for epidemiological investigations.

Review Global seroprevalence of legionellosis - a systematic review and meta-analysis

Legionella is a ubiquitous pathogen yet the global occurrence of legionellosis is poorly understood. To address this deficit, this paper summarises the available evidence on the seroprevalence of Legionella antibodies and explores factors that may influence seroprevalence estimates. Through a systematic review, a total of 3979 studies were identified with seroprevalence results published after 1 January 1990. We tabulated findings by World Health Organization (WHO) region, location, study period and design, composition of study population(s) for all ages in terms of exposure, sex, detection methods, IFA titre, Legionella species measured, and present seroprevalence point estimates and 95% confidence intervals. Sampled populations were classified according to income, WHO region, gender, age, occupation and publication date. We conducted a meta-analysis on these subgroups using Comprehensive Meta-Analysis 3.0 software. Heterogeneity across studies was evaluated by the Q test in conjunction with I² statistics. Publication bias was evaluated via funnel plot and Egger's test. Fifty-seven studies met our inclusion criteria, giving an overall estimate of seroprevalence for Legionella of 13.7% (95% CI 11.3-16.5), but with substantial heterogeneity across studies.