The Presence of (1→3)-β-D-Glucan as Prognostic Marker in Patients After Major Abdominal Surgery

Developments in Fungal Serology

Purpose of Review

The true incidence of fungal disease is hampered by conventionally poor diagnostic tests, limited access to advanced diagnostics, and limited surveillance. The availability of serological testing has been available for over two decades and generally underpins the modern diagnosis of the most common forms of fungal disease. This review will focus on technical developments of serological tests for the diagnosis of fungal disease, describing advances in clinical performance when available.

Recent Findings

Despite their longevity, technical, clinical, and performance limitations remain, and tests specific for fungal pathogens outside the main pathogens are lacking. The availability of LFA and automated systems, capable of running multiple different tests, represents significant developments, but clinical performance data is variable and limited.

Summary

Fungal serology has significantly advanced the diagnosis of the main fungal infections, with LFA availability increasing accessibility to testing. Combination testing has the potential to overcome performance limitations.

Combined Use of Presepsin and (1,3)-β-D-glucan as Biomarkers for Diagnosing Candida Sepsis and Monitoring the Effectiveness of Treatment in Critically Ill Patients

New biomarker panel was developed and validated on 165 critically ill adult patients to enable a more accurate invasive candidiasis (IC) diagnosis. Serum levels of the panfungal biomarker (1,3)-β-D-glucan (BDG) and the inflammatory biomarkers C-reactive protein, presepsin (PSEP), and procalcitonin (PCT) were correlated with culture-confirmed candidemia or bacteremia in 58 and 107 patients, respectively. The diagnostic utility was evaluated in sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). BDG was the best marker for IC, achieving 96.6% sensitivity, 97.2% specificity, 94.9% PPV, and 98.1% NPV at a cut-off of 200 pg/mL (p ≤ 0.001). PSEP exhibited 100% sensitivity and 100% NPV at a cut-off of 700 pg/mL but had a lower PPV (36.5%) and low specificity (5.6%). Combined use of PSEP and BDG, thus, seems to be the most powerful laboratory approach for diagnosing IC. Furthermore, PSEP was more accurate for 28-day mortality prediction the area under the receiver operating characteristic curve (AUC = 0.74) than PCT (AUC = 0.31; PCT cut-off = 0.5 ng/mL). Finally, serum PSEP levels decreased significantly after only 14 days of echinocandin therapy (p = 0.0012). The probability of IC is almost 100% in critically ill adults with serum BDG and PSEP concentrations > 200 pg/mL and >700 pg/mL, respectively, defining a borderline between non-invasive superficial Candida colonization and IC.

Diagnosis and Management of Invasive Candida Infections in Critically Ill Patients

Invasive candidiasis (IC) has become a serious problem in the intensive care unit patients with an attributable mortality rate that can reach up to 51%. Multiple global surveillance studies have shown an increasing incidence of candidemia. Despite their limited sensitivity (21-71%), cultures remain the gold standard for the diagnosis of IC associated with candidemia. Many adjunct laboratory tests exist to support or rule out the diagnosis, each with its indications and limitations, including procalcitonin, 1,3-β-D-glucan, mannan and anti-mannan antibodies, and Candida albicans germ tube antibody. In addition, polymerase chain reaction-based methods could expedite species identification in positive blood cultures, helping in guiding early empirical antifungal therapy. The management of IC in critically ill patients can be classified into prophylactic, preemptive, empiric, and directed/targeted therapy of a documented infection. There is no consensus concerning the benefit of prophylactic therapy in critically ill patients. While early initiation of appropriate therapy in confirmed IC is an important determinant of survival, the selection of candidates and drug of choice for empirical systemic antifungal therapy is more controversial. The choice of antifungal agents is determined by many factors, including the host, the site of infection, the species of the isolated Candida, and its susceptibility profile. Echinocandins are considered initial first-line therapy agents. Due to the conflicting results of the various studies on the benefit of preemptive therapy for critically ill patients and the lack of robust evidence, the Infectious Diseases Society of America (IDSA) omitted this category from its updated guidelines and the European Society of Intensive Care Medicine (ESICM) and the Critically Ill Patients Study Group of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) do not recommend it.

Evaluation of the Performance of the Associates of Cape Cod STAT Assay for the Diagnosis of Invasive Fungal Disease in Critical-Care Patients with COVID-19

During the COVID-19 pandemic, there have been increasing reports of invasive fungal disease (IFD) in critical care, where rapid access to (1-3)-β-d-glucan (BDG) testing may have enhanced diagnosis. The potential benefit of rapidly accessible BDG results is limited by local availability of BDG testing, with low demand resulting in testing being performed in specialist centers. The recent release of the Associates of Cape Cod STAT assay provides a simple, low-throughput BDG platform, potentially increasing accessibility. During the pandemic, BDG testing using the Fungitell assay (FA) was a critical component of screening for IFD in our critical care. The performance of the STAT was retrospectively determined through a case-control study of 107 serum samples from critical-care COVID-19 patients with IFD defined according to international guidelines. The STAT demonstrated excellent qualitative (observed agreement, 97.2%; kappa, 0.94) and quantitative (Spearman's coefficient, 0.8962) agreement with the FA. Sample positivity was greater (P < 0.0001) in samples from cases (67.7%) versus controls (6.1%). Using the manufacturer's threshold (≥1.2), sensitivity and specificity for the detection of proven/probable IFD were 67.9% and 93.9%, respectively. Using a lower positivity threshold of ≥0.87 increased sensitivity to 71.4% without compromising specificity. When the STAT BDG index was >2.86, specificity was 100%. The STAT provides a simple, comparable alternative to the FA for detecting BDG. Sensitivity is moderate, and specificity is excellent for the diagnosis of IFD in the critical-care COVID-19 patient. The potential for enhancing access to BDG testing through the uptake of STAT at centers where FA is not available is beneficial, especially during the COVID-19 pandemic.

Recent Advances and Novel Approaches in Laboratory-Based Diagnostic Mycology

What was once just culture and microscopy the field of diagnostic mycology has significantly advanced in recent years and continues to incorporate novel assays and strategies to meet the changes in clinical demand. The emergence of widespread resistance to antifungal therapy has led to the development of a range of molecular tests that target mutations associated with phenotypic resistance, to complement classical susceptibility testing and initial applications of next-generation sequencing are being described. Lateral flow assays provide rapid results, with simplicity allowing the test to be performed outside specialist centres, potentially as point-of-care tests. Mycology has responded positively to an ever-diversifying patient population by rapidly identifying risk and developing diagnostic strategies to improve patient management. Nowadays, the diagnostic repertoire of the mycology laboratory employs classical, molecular and serological tests and should be keen to embrace diagnostic advancements that can improve diagnosis in this notoriously difficult field.

Specificity Influences in (1→3)-β-d-Glucan-Supported Diagnosis of Invasive Fungal Disease

(1→3)-β-glucan (BDG) testing as an adjunct in the diagnosis of invasive fungal disease (IFD) has been in use for nearly three decades. While BDG has a very high negative predictive value in this setting, diagnostic false positives may occur, limiting specificity and positive predictive value. Although results may be diagnostically false positive, they are analytically correct, due to the presence of BDG in the circulation. This review surveys the non-IFD causes of elevated circulating BDG. These are in the main, iatrogenic patient contamination through the use of BDG-containing medical devices and parenterally-delivered materials as well as translocation of intestinal luminal BDG due to mucosal barrier injury. Additionally, infection with Nocardia sp. may also contribute to elevated circulating BDG. Knowledge of the factors which may contribute to such non-IFD-related test results can improve the planning and interpretation of BDG assays and permit investigational strategies, such as serial sampling and BDG clearance evaluation, to assess the likelihood of contamination and improve patient care.