Rapid diagnosis of invasive candidiasis: ready for prime-time?

Performance of a Real-Time PCR Assay for the Detection of Five Candida Species in Blood Samples from ICU Patients at Risk of Candidemia

The gold standard for diagnosing invasive candidiasis still relies on blood cultures, which are inefficient and time-consuming to analyze. We developed an in-house qPCR assay to identify the 5 major Candida species in 78 peripheral blood (PB) samples from ICU patients at risk of candidemia. Blood cultures and (1,3)-β-D-glucan (BDG) testing were performed concurrently to evaluate the performance of the qPCR. The qPCR was positive for DNA samples from all 20 patients with proven candidemia (positive PB cultures), showing complete concordance with Candida species identification in blood cultures, except for detection of dual candidemia in 4 patients, which was missed by blood cultures. Additionally, the qPCR detected Candida species in six DNA samples from patients with positive central venous catheters blood (CB) but negative PB cultures. BDG values were similarly high in these six samples and the ones with proven candidemia, strongly suggesting the diagnosis of a true candidemia episode despite the negative PB cultures. Samples from patients neither infected nor colonized yielded negative results in both the qPCR and BDG testing. Our qPCR assay was at least as sensitive as blood cultures, but with a shorter turnaround time. Furthermore, negative results from the qPCR provided strong evidence for the absence of candidemia caused by the five major Candida species.

Diagnosis and Antifungal Prophylaxis for COVID-19 Associated Pulmonary Aspergillosis

The COVID-19 pandemic has redemonstrated the importance of the fungal-after-viral phenomenon, and the question of whether prophylaxis should be used to prevent COVID-19-associated pulmonary aspergillosis (CAPA). A distinct pathophysiology from invasive pulmonary aspergillosis (IPA), CAPA has an incidence that ranges from 5% to 30%, with significant mortality. The aim of this work was to describe the current diagnostic landscape of CAPA and review the existing literature on antifungal prophylaxis. A variety of definitions for CAPA have been described in the literature and the performance of the diagnostic tests for CAPA is limited, making diagnosis a challenge. There are only six studies that have investigated antifungal prophylaxis for CAPA. The two studied drugs have been posaconazole, either a liquid formulation via an oral gastric tube or an intravenous formulation, and inhaled amphotericin. While some studies have revealed promising results, they are limited by small sample sizes and bias inherent to retrospective studies. Additionally, as the COVID-19 pandemic changes and we see fewer intubated and critically ill patients, it will be more important to recognize these fungal-after-viral complications among non-critically ill, immunocompromised patients. Randomized controlled trials are needed to better understand the role of antifungal prophylaxis.

Performance of Multiplex PCR and β-1,3-D-Glucan Testing for the Diagnosis of Candidemia

Bloodstream infections caused by Candida yeasts (candidemia) are associated with high morbidity and mortality. Diagnosis remains challenging, with the current gold standard—isolation from blood culture (BC)—being limited by low sensitivity and long turnaround time. This study evaluated the performance of two nonculture methods: PCR and β-1,3-D-glucan (BDG) testing. The sera of 103 patients with BC-proven candidemia and of 46 controls were analyzed with the Fungiplex Candida Real-Time PCR and the Wako β-Glucan Test. The BDG assay demonstrated higher sensitivity than the multiplex PCR (58% vs. 33%). This was particularly evident in ICU patients (60% vs. 28%) and in C. albicans candidemia (57% vs. 37%). The earlier prior to BC sampling the sera were obtained, the more the PCR sensitivity decreased (46% to 18% in the periods of 0−2 and 3−5 days before BC, respectively), while BDG testing was independent of the sampling date. No positive PCR results were obtained in sera sampled more than five days before BC. Specificities were 89% for BDG and 93% for PCR testing. In conclusion, BDG testing demonstrated several advantages over PCR testing for the diagnosis of candidemia, including higher sensitivity and earlier diagnosis. However, BC remains essential, as BDG does not allow for species differentiation.

Continuing Shifts in Epidemiology and Antifungal Susceptibility Highlight the Need for Improved Disease Management of Invasive Candidiasis

Invasive candidiasis (IC) is a systemic life-threatening infection of immunocompromised humans, but remains a relatively neglected disease among public health authorities. Ongoing assessments of disease epidemiology are needed to identify and map trends of importance that may necessitate improvements in disease management and patient care. Well-established incidence increases, largely due to expanding populations of patients with pre-disposing risk factors, has led to increased clinical use and pressures on antifungal drugs. This has been exacerbated by a lack of fast, accurate diagnostics that have led treatment guidelines to often recommend preventative strategies in the absence of proven infection, resulting in unnecessary antifungal use in many instances. The consequences of this are multifactorial, but a contribution to emerging drug resistance is of primary concern, with high levels of antifungal use heavily implicated in global shifts to more resistant Candida strains. Preserving and expanding the utility and number of antifungals should therefore be of the highest priority. This may be achievable through the development and use of biomarker tests, bringing about a new era in improved antifungal stewardship, as well as novel antifungals that offer favorable profiles by targeting Candida pathogenesis mechanisms over cell viability.

Noninvasive Testing and Surrogate Markers in Invasive Fungal Diseases

Invasive fungal infections continue to increase as at-risk populations expand. The high associated morbidity and mortality with fungal diseases mandate the continued investigation of novel antifungal agents and diagnostic strategies that include surrogate biomarkers. Biologic markers of disease are useful prognostic indicators during clinical care, and their use in place of traditional survival end points may allow for more rapid conduct of clinical trials requiring fewer participants, decreased trial expense, and limited need for long-term follow-up. A number of fungal biomarkers have been developed and extensively evaluated in prospective clinical trials and small series. We examine the evidence for these surrogate biomarkers in this review and provide recommendations for clinicians and regulatory authorities.

Coronavirus disease 2019 (COVID-19) associated pulmonary aspergillosis (CAPA): Re-framing the debate

Background

Coronavirus disease 2019 (COVID-19)-associated pulmonary aspergillosis (CAPA) has been reported in ~5%–10% of critically ill COVID-19 patients. However, incidence varies widely (0%–33%) across hospitals, most cases are unproven, and CAPA definitions and clinical relevance are debated.

Methods

We reframed the debate by asking, what is the likelihood that patients with CAPA have invasive aspergillosis? We use diagnostic test performance in other clinical settings to estimate positive predictive values (PPVs) and negative predictive values (NPVs) of CAPA criteria for invasive aspergillosis in populations with varying CAPA incidence.

Results

In a population with CAPA incidence of 10%, anticipated PPV/NPV of diagnostic criteria are ~30%–60%/≥97%; ~3%–5% of tested cohort would be anticipated to have true invasive aspergillosis. If CAPA incidence is 2%–3%, anticipated PPV and NPV are ~8%–30%/>99%.

Conclusions

Depending on local epidemiology and clinical details of a given case, PPVs and NPVs may be useful in guiding antifungal therapy. We incorporate this model into a stepwise strategy for diagnosing and managing CAPA.

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.

Protocol for the pBDG2 Study: Prospective Evaluation of 1.3-β-D-Glucan in the Peritoneal Fluid for the Diagnosis of Intra-Abdominal Candidiasis in Critically Ill Patients

Background: The delayed diagnosis of the presence of Candida in severe intra-abdominal infections exposes patients to an increased risk of mortality. The prevalence of intra-abdominal candidiasis (IAC) varies with the type of intra-abdominal infection, the underlying conditions and the presence of risk factors for Candida infection. This study aims to evaluate the interest of the measure of 1.3-β-D-glucan (BDG) in the peritoneal fluid for the early diagnosis of IAC. Methods and analysis: This is a prospective multicenter (n = 5) non-interventional study, focusing on all critically ill patients with an intra-abdominal infection requiring intra-abdominal surgery. The primary objective is to assess the diagnostic performance of the BDG measured in the peritoneal fluid for the early detection of IAC using the Candida culture as the gold standard. The secondary objective is to report the prevalence of IAC in the selected population. This study aims to enroll 200 patients within 48 months. By estimating the prevalence of IAC in the selected population at 30%, 50 patients with IAC (cases) are expected. These 50 IAC cases will be matched with 50 non-IAC patients (as a control group). The peritoneal BDG will be measured a posteriori in all of these 100 selected patients. This article presents the protocol and the current status of the study. Only the prevalence of IAC is reported as preliminary result.

Molecular Diagnosis of Yeast Infections

PURPOSE OF REVIEW

The use of molecular tests to aid the diagnosis of invasive yeast infection, in particular invasive candidosis, has been described for over two decades, yet widespread application is limited, and diagnosis remains heavily dependent on classical microbiology. This article will review developments from the past decade in attempt to build on existing knowledge. It will highlight clinical performance and limitations while reviewing developments on recognized procedures; it will also provide insight into novel approaches incorporated in response to clinical demand (e.g. C. auris and antifungal resistance) or technological advances (e.g. next-generation sequencing).

RECENT FINDINGS

Limited methodological standardization and, until recently, unavailability of commercial options have hindered the integration of molecular diagnostics for yeasts. The development of certain, novel commercial methods has received considerable evaluation allowing a greater understanding of individual assay performance, but widespread multicentre evaluation of most commercial kits is lacking. The detection of emerging pathogens (e.g. C. auris) has been enhanced by the development of molecular tests. Molecular methods are providing a better understanding of the mycobiome, mechanisms of resistance and epidemiology/phylogeny.

SUMMARY

Despite over two decades of use, the incorporation of molecular methods to enhance the diagnosis of yeast infections remains limited to certain specialist centres. While the development of commercial tests will provide stimulus for broader application, further validation and reduced costs are required. Over the same period of time, Aspergillus PCR has become more widely accepted driven by international efforts to standardize methodology; it is critical that yeast PCR follows suit. Next-generation sequencing will provide significant information on the mycobiome, antifungal resistance mechanism and even broad-range detection directly from the specimen, which may be critical for the molecular detection of yeasts other than Candida species, which is currently limited.

Diagnosis of Breakthrough Fungal Infections in the Clinical Mycology Laboratory: An ECMM Consensus Statement

Breakthrough invasive fungal infections (bIFI) cause significant morbidity and mortality. Their diagnosis can be challenging due to reduced sensitivity to conventional culture techniques, serologic tests, and PCR-based assays in patients undergoing antifungal therapy, and their diagnosis can be delayed contributing to poor patient outcomes. In this review, we provide consensus recommendations on behalf of the European Confederation for Medical Mycology (ECMM) for the diagnosis of bIFI caused by invasive yeasts, molds, and endemic mycoses, to guide diagnostic efforts in patients receiving antifungals and support the design of future clinical trials in the field of clinical mycology. The cornerstone of lab-based diagnosis of breakthrough infections for yeast and endemic mycoses remain conventional culture, to accurately identify the causative pathogen and allow for antifungal susceptibility testing. The impact of non-culture-based methods are not well-studied for the definite diagnosis of breakthrough invasive yeast infections. Non-culture-based methods have an important role for the diagnosis of breakthrough invasive mold infections, in particular invasive aspergillosis, and a combination of testing involving conventional culture, antigen-based assays, and PCR-based assays should be considered. Multiple diagnostic modalities, including histopathology, culture, antibody, and/or antigen tests and occasionally PCR-based assays may be required to diagnose breakthrough endemic mycoses. A need exists for diagnostic tests that are effective, simple, cheap, and rapid to enable the diagnosis of bIFI in patients taking antifungals.