Implementation of Lateral Flow Assays for the Diagnosis of Invasive Aspergillosis in European Hospitals: A Survey from Belgium and a Literature Review of Test Performances in Different Patient Populations

OBJECTIVES

Diagnosis of invasive aspergillosis is based on a combination of criteria, of which the detection of Aspergillus galactomannan (GM) often is decisive. To date, the most commonly used method to determine GM is an enzyme-linked immune assay (EIA). But since a few years lateral flow assays (LFAs) were introduced, providing the possibility for rapid single sample testing. More and more LFAs are entering the market, but, although often being equated, all use their own antibodies, procedures and interpretation criteria. A recent European survey revealed that about 24-33% of laboratories implemented a lateral flow assay on-site.

METHODS

We conducted a survey at 81 Belgian hospital laboratories regarding the implementation of LFAs in their centre. In addition, we performed an extensive review of all publicly available studies on the performance of lateral flow assays to diagnose invasive aspergillosis.

RESULTS

Response rate to the survey was 69%. Of the 56 responding hospital laboratories, 6 (11%) used an LFA. The Soña Aspergillus galactomannan LFA (IMMY, Norman, Oklahoma, USA) was used in 4/6 centres, while two centres used the QuicGM (Dynamiker, Tianjin, China) and one centre used the FungiXpert Aspergillus Galactomannan Detection K-set LFA (Genobio [Era Biology Technology], Tianjin, China). One centre used 2 distinct LFAs. In 3/6 centres, the sample is sent to another lab for confirmation with GM-EIA when the LFA result is positive and in 2/6 when the LFA results is negative. In one centre, a confirmatory GM-EIA is always performed in house. In three centres the LFA result is used as a complete substitute for GM-EIA. Available LFA performance studies are very diverse and results vary in function of the study population and type of LFA. Apart from the IMMY and OLM LFA, only very limited performance data are available. From two out of three LFAs used in Belgium, no clinical performance studies are published in literature.

CONCLUSIONS

A large variety of LFAs are used in Belgian Hospitals, some of which no clinical validation studies are published. These results do likely have implications for other parts of Europe and for the rest of the world as well. Due to the variable performance of LFA tests and the limited validation data available, each laboratory must check the available performance information of the specific test considered for implementation. In addition, laboratories should perform an implementation verification study.

The diagnostic and clinical utility of microbial cell-free DNA sequencing in a real-world setting

Microbial cell free DNA sequencing is increasingly used for diagnosis of infection but few studies describe its utility in real-world settings. We performed a single-center retrospective case series of microbial cell free DNA testing using the Karius assay from 29 patient samples to define the clinical reasoning and the impact of testing. Indications fell into 3 categories, identifying a causative pathogen in patients with an infectious syndrome and negative microbiologic workup (15/29, 52%), seeking another pathogen when organisms identified by traditional diagnostics failed to explain the clinical presentation (9/29, 31%) and to "rule out" infection in patients with nonspecific symptoms and negative microbiologic workup (5/29, 17%). Clinical impact was positive in 13/29 (45%) and all were for patients with high pretest probability for infection. Impact was negative in 3/29 (10%) cases. There was no impact in 15/29 (52%) cases. Further work is needed to define the optimal timing accounting for test performance, and patient characteristics.

Diagnosis of invasive fungal infections: challenges and recent developments

BACKGROUND

The global burden of invasive fungal infections (IFIs) has shown an upsurge in recent years due to the higher load of immunocompromised patients suffering from various diseases. The role of early and accurate diagnosis in the aggressive containment of the fungal infection at the initial stages becomes crucial thus, preventing the development of a life-threatening situation. With the changing demands of clinical mycology, the field of fungal diagnostics has evolved and come a long way from traditional methods of microscopy and culturing to more advanced non-culture-based tools. With the advent of more powerful approaches such as novel PCR assays, T2 Candida, microfluidic chip technology, next generation sequencing, new generation biosensors, nanotechnology-based tools, artificial intelligence-based models, the face of fungal diagnostics is constantly changing for the better. All these advances have been reviewed here giving the latest update to our readers in the most orderly flow.

MAIN TEXT

A detailed literature survey was conducted by the team followed by data collection, pertinent data extraction, in-depth analysis, and composing the various sub-sections and the final review. The review is unique in its kind as it discusses the advances in molecular methods; advances in serology-based methods; advances in biosensor technology; and advances in machine learning-based models, all under one roof. To the best of our knowledge, there has been no review covering all of these fields (especially biosensor technology and machine learning using artificial intelligence) with relevance to invasive fungal infections.

CONCLUSION

The review will undoubtedly assist in updating the scientific community's understanding of the most recent advancements that are on the horizon and that may be implemented as adjuncts to the traditional diagnostic algorithms.

Dynamic full-field optical coherence tomography as complementary tool in fungal diagnostics

Histopathology and microscopic examination of infected tissue are the gold standards to prove the diagnosis of invasive fungal infection (IFI). Yet, they suffer from essential limitations that hamper rapid diagnosis and require the future development of new imaging tools dedicated to fungal diagnostics. To this end, the present work introduces the first use of dynamic full-field optical coherence tomography (D-FF-OCT) for the visualization of microscopic filamentous fungi. Data collected from the observation of three different fungal species (Nannizzia gypsea, Aspergillus fumigatus and Rhizopus arrhizus) confirm the ability of D-FF-OCT to visualize not only the main structures of all selected fungal species (hyphae, spores, conidia, sporulating structures), but also the metabolic activity of the organisms, which could provide additional help in the future to better characterize the signature of each fungal structure. These results demonstrate how D-FF-OCT could serve as potential complementary tool for rapid diagnosis of IFI in both intensive and non-intensive care units.

The host transcriptional response to Candidemia is dominated by neutrophil activation and heme biosynthesis and supports novel diagnostic approaches

BACKGROUND

Candidemia is one of the most common nosocomial bloodstream infections in the United States, causing significant morbidity and mortality in hospitalized patients, but the breadth of the host response to Candida infections in human patients remains poorly defined.

METHODS

In order to better define the host response to Candida infection at the transcriptional level, we performed RNA sequencing on serial peripheral blood samples from 48 hospitalized patients with blood cultures positive for Candida species and compared them to patients with other acute viral, bacterial, and non-infectious illnesses. Regularized multinomial regression was utilized to develop pathogen class-specific gene expression classifiers.

RESULTS

Candidemia triggers a unique, robust, and conserved transcriptomic response in human hosts with 1641 genes differentially upregulated compared to healthy controls. Many of these genes corresponded to components of the immune response to fungal infection, heavily weighted toward neutrophil activation, heme biosynthesis, and T cell signaling. We developed pathogen class-specific classifiers from these unique signals capable of identifying and differentiating candidemia, viral, or bacterial infection across a variety of hosts with a high degree of accuracy (auROC 0.98 for candidemia, 0.99 for viral and bacterial infection). This classifier was validated on two separate human cohorts (auROC 0.88 for viral infection and 0.87 for bacterial infection in one cohort; auROC 0.97 in another cohort) and an in vitro model (auROC 0.94 for fungal infection, 0.96 for bacterial, and 0.90 for viral infection).

CONCLUSIONS

Transcriptional analysis of circulating leukocytes in patients with acute Candida infections defines novel aspects of the breadth of the human immune response during candidemia and suggests promising diagnostic approaches for simultaneously differentiating multiple types of clinical illnesses in at-risk, acutely ill patients.

Detection of the 'Big Five' mold killers of humans: Aspergillus, Fusarium, Lomentospora, Scedosporium and Mucormycetes

Fungi are an important but frequently overlooked cause of morbidity and mortality in humans. Life-threatening fungal infections mainly occur in immunocompromised patients, and are typically caused by environmental opportunists that take advantage of a weakened immune system. The filamentous fungus Aspergillus fumigatus is the most important and well-documented mold pathogen of humans, causing a number of complex respiratory diseases, including invasive pulmonary aspergillosis, an often fatal disease in patients with acute leukemia or in immunosuppressed bone marrow or solid organ transplant recipients. However, non-Aspergillus molds are increasingly reported as agents of disseminated diseases, with Fusarium, Scedosporium, Lomentospora and mucormycete species now firmly established as pathogens of immunosuppressed and immunocompetent individuals. Despite well-documented risk factors for invasive fungal diseases, and increased awareness of the risk factors for life-threatening infections, the number of deaths attributable to molds is likely to be severely underestimated driven, to a large extent, by the lack of readily accessible, cheap, and accurate tests that allow detection and differentiation of infecting species. Early diagnosis is critical to patient survival but, unlike Aspergillus diseases, where a number of CE-marked or FDA-approved biomarker tests are now available for clinical diagnosis, similar tests for fusariosis, scedosporiosis and mucormycosis remain experimental, with detection reliant on insensitive and slow culture of pathogens from invasive bronchoalveolar lavage fluid, tissue biopsy, or from blood. This review examines the ecology, epidemiology, and contemporary methods of detection of these mold pathogens, and the obstacles to diagnostic test development and translation of novel biomarkers to the clinical setting.

Aspergillus galactomannan detection in exhaled breath condensate compared to bronchoalveolar lavage fluid for the diagnosis of invasive aspergillosis in immunocompromised patients

OBJECTIVES

Exhaled breath condensate (EBC) is a noninvasive means of sampling the airways that has shown significant promise in the diagnosis of many disorders. There have been no reports of its usefulness in the detection of galactomannan (GM), a component of the cell wall of Aspergillus. The suitability of EBC for the detection of GM for the diagnosis of invasive aspergillosis (IA) using the Platelia Aspergillus enzyme-linked immunosorbent assay was investigated.

METHODS

Prospective, cross-sectional study of lung transplant recipient and haemotologic malignancy patients at a university centre. EBC samples were compared to concomitant bronchoalveolar lavage (BAL) samples among lung transplant recipients and healthy controls. EBC was collected over 10 minutes using a refrigerated condenser according to the European Respiratory Society/American Thoracic Society recommendations, with the BAL performed immediately thereafter.

RESULTS

A total of 476 EBC specimens with 444 matched BAL specimens collected from lung transplant recipients (n = 197) or haemotologic malignancy patients (n = 133) were examined. Both diluted and untreated EBC optical density (OD) values (0.0830, interquartile range (IQR) 0.0680-0.1040; and 0.1130, IQR 0.0940-0.1383), respectively, from all patients regardless of clinical syndrome were significantly higher than OD values in healthy control EBCs (0.0508, IQR 0.0597-0.0652; p < 0.0001). However, the OD index values did not correlate with the diagnosis of IA (44 samples were associated with IA). Furthermore, no significant correlation was found between EBC GM and the matched BAL specimen.

CONCLUSIONS

GM is detectable in EBC; however, no correlation between OD index values and IA was noted in lung transplant recipients.

Distinct galactofuranose antigens in the cell wall and culture supernatants as a means to differentiate Fusarium from Aspergillus species

Detection of carbohydrate antigens is an important means for diagnosis of invasive fungal infections. For diagnosis of systemic Aspergillus infections, galactomannan is commonly used, the core antigenic structure of which consists of chains of several galactofuranose moieties. In this study, we provide evidence that Fusarium produces at least two distinct galactofuranose antigens: Smaller amounts of galactomannan and larger quantities of a novel antigen recognized by the monoclonal antibody AB135-8. In A. fumigatus, only minor amounts of the AB135-8 antigen are found in supernatants and in the apical regions of hyphae. A galactofuranose-deficient A. fumigatus mutant lacks the AB135-8 antigen, which strongly suggests that galactofuranose is an essential constituent of this antigen. Using a combination of AB135-8 and a galactomannan-specific antibody, we were able to unambiguously differentiate A. fumigatus and Fusarium hyphae in immunohistology. Moreover, since Fusarium releases the AB135-8 antigen, it appears to be a promising target antigen for a serological detection of Fusarium infections.