Polymerase chain reaction blood tests for the diagnosis of invasive aspergillosis in immunocompromised people

Advances in the diagnosis of fungal pneumonias

INTRODUCTION

Fungal infections are increasingly encountered in clinical practice due to more favorable environmental conditions and increasing prevalence of immunocompromised individuals. The diagnostic approach for many fungal pathogens continues to evolve. Herein, we outline available diagnostic tests for the most common fungal infections with a focus on recent advances and future directions.

AREAS COVERED

We discuss the diagnostic testing methods for angioinvasive molds (Aspergillus spp. and Mucor spp.), invasive yeast (Candida spp. and Cryptococcus ssp.), Pneumocystis, and endemic fungi (Blastomyces sp., Coccidioides ssp., and Histoplasma sp.). The PubMed-NCBI database was searched within the past 5 years to identify the most recent available literature with dates extended in cases where literature was sparse. Diagnostic guidelines were utilized when available with references reviewed.

EXPERT OPINION

Historically, culture and/or direct visualization of fungal organisms were required for diagnosis of infection. Significant limitations included ability to collect specimens and delayed diagnosis associated with waiting for culture results. Antigen and antibody testing have made great strides in allowing quicker diagnosis of fungal infections but can be limited by low sensitivity/specificity, cross-reactivity with other fungi, and test availability. Molecular methods have a rich history in some fungal diseases, while others continue to be developed.

Molecular Diagnostic Advances in Transplant Infectious Diseases

PURPOSE OF REVIEW

The infectious complications of transplantation can have devastating consequences for patients. Early and accurate diagnosis is essential to good outcomes. This review describes recent advances in pathogen-directed diagnostic testing and discusses the role of new methods for transplant infectious diseases.

RECENT FINDINGS

Several molecular assays have been introduced into clinical practice in recent years. When the results of rapid testing are linked to patient-specific interventions, improved outcomes can be realized. Syndromic testing along with metagenomic next-generation sequencing (mNGS) represents novel approaches to infection diagnosis. However, the optimal use of these tests for transplant patients along with an overall assessment of cost-effectiveness demands further study. Molecular diagnostics are revolutionizing transplant care. Clinicians need to be aware of the current diagnostic landscape and have a working knowledge of the nuances related to test performance, result interpretation, and cost.

New Concepts in Diagnostics for Invasive Mycoses: Non-Culture-Based Methodologies

Non-culture-based diagnostics have been developed to help establish an early diagnosis of invasive fungal infection. Studies have shown that these tests can significantly impact the diagnosis of infection in high risk patients. Aspergillus galactomannan EIA testing is well-recognized as an important adjunct to the diagnosis of invasive aspergillosis and can be detected in serum, bronchoalveolar lavage and other fluids. Galactomannan testing used along with PCR testing has been shown to be effective when integrated into care paths for high risk patients for both diagnoses and as a surrogate marker for outcome when used in serial testing. Beta-d-glucan assays are non-specific for several fungal genera including Aspergillus and Candida and in high risk patients have been an important tool to augment the diagnosis. Lateral flow technology using monoclonal antibodies to Aspergillus are available that allow rapid testing of clinical samples. While standard PCR for Candida remains investigational, T2 magnetic resonance allows for the rapid diagnosis of Candida species from blood cultures. Aspergillus PCR has been extensively validated with standardized approaches established for these methods and will be included in the diagnostic criteria in the revised European Organization for Research and Treatment of Cancer/Mycoses Study Group (EORTC-MSG) definitions. Finally, these non-culture-based tests can be used in combination to significantly increase the detection of invasive mycoses with the ultimate aim of establishing an early diagnosis of infection.

Sputum signatures for invasive pulmonary aspergillosis in patients with underlying respiratory diseases (SPARED): study protocol for a prospective diagnostic trial

BACKGROUND

Invasive pulmonary aspergillosis (IPA) has been increasingly reported in patients with underlying respiratory diseases (URD). Early diagnosis of IPA is crucial for mortality reduction and improved prognosis, yet remains difficult. Existing diagnostic tools for IPA largely rely on the detection of biomarkers based on serum or bronchoalveolar lavage fluid (BALF), both of which have their limitations. The use of sputum sample is non-invasive, and Aspergillus detection is feasible; however, the usefulness of sputum biomarkers for the diagnosis of IPA, especially in patients with URD, has not been systematically studied.

METHODS

This is a prospective diagnostic trial. At least 118 participants will be recruited from respiratory wards and intensive care units. IPA is defined according to the EORTC/MSG criteria modified for patients with URD. Induced sputum and blood will be collected, and BALF will be obtained by bronchoscopy. Sputum biomarkers, including galactomannan, Aspergillus DNA, triacetylfusarinine and bis(methylthio)gliotoxin will be determined, and the presence of a JF5 antigen will be examined with a lateral fluid device. The sensitivity, specificity, negative predictive value, positive predictive value and diagnostic odds ratio will be computed for different biomarkers and compared using the McNemar χ2 test. Receiver operating characteristic analyses will be performed, and the cut-off values will be established. Participants will receive follow-up evaluations at 3 months and 6 months after recruitment. The difference in hospital stay and survival will be analysed, and the relationships between the levels of biomarkers and hospital stay and survival will be analysed via regression models.

DISCUSSION

We have developed and verified the feasibility of Aspergillus-related biomarker assays for sputum. The study findings will contribute to a novel look at the diagnostic performance of sputum biomarkers in IPA and provide important insight into the improvement of the early diagnosis of IPA, particularly in patients with URD.

TRIAL REGISTRATION

This study has been registered with the Chinese Clinical Trial Registry ( ChiCTR-DPD-16009070 ) on 24th of August 2016.

Evaluation of the diagnostic performance of panfungal polymerase chain reaction assay in invasive fungal diseases

Timely diagnosis of invasive fungal diseases (IFDs) is important, as delays in treatment initiation are associated with increased mortality rates. However, early diagnosis of IFDs in immunocompromised patients remains difficult. The conventional diagnostic methods currently used for IFDs are not sufficiently effective. Molecular tests, such as polymerase chain reaction (PCR)-based assays, have great potential to improve the early diagnosis of IFDs due to their sensitivity and specificity. In the present study, the diagnostic performance of panfungal PCR assays in IFD patients who received bone marrow transplantation was evaluated. The results suggested that panfungal PCR assay offered a quick and convenient guide for clinical decision-making by identifying higher numbers of fungal species in comparison with the conventional blood culture method. Furthermore, panfungal PCR assay exhibited a sensitivity of 93% and a specificity of 71% in the diagnosis of IFD patients based on the EORTC/MSG criteria. Thus, the present study concluded that the reported PCR-based method was effective and sensitive in early IFD diagnosis and should be integrated into clinical decision-making for the treatment of IFDs in the future.

Antifungal stewardship considerations for adults and pediatrics

Antifungal stewardship refers to coordinated interventions to monitor and direct the appropriate use of antifungal agents in order to achieve the best clinical outcomes and minimize selective pressure and adverse events. Antifungal utilization has steadily risen over time in concert with the increase in number of immunocompromised adults and children at risk for invasive fungal infections (IFI). Challenges in diagnosing IFI often lead to delays in treatment and poorer outcomes. There are also emerging data linking prior antifungal exposure and suboptimal dosing to the emergence of antifungal resistance, particularly for Candida. Antimicrobial stewardship programs can take a multi-pronged bundle approach to ensure suitable prescribing of antifungals via post-prescription review and feedback and/or prior authorization. Institutional guidelines can also be developed to guide diagnostic testing in at-risk populations; appropriate choice, dose, and duration of antifungal agent; therapeutic drug monitoring; and opportunities for de-escalation and intravenous-to-oral conversion.

Laboratory Diagnostics for Fungal Infections: A Review of Current and Future Diagnostic Assays

This article reviews the current diagnostic approaches, both serologic and molecular, for the detection of fungi associated with pulmonary disease. Classic serologic techniques, including immunodiffusion and complement fixation, both of which remain a cornerstone for fungal diagnostic testing, are reviewed and their performance characteristics presented. More recent advances in this field, including novel lateral-flow assays for fungal antigen detection, are also described. Molecular techniques for fungal identification both from culture and directly from patient specimens, including nucleic acid probes, mass spectrometry-based methods, nucleic acid amplification testing, and traditional and broad-range sequencing, are discussed and their performance evaluated.

Progress in the Diagnosis of Invasive Fungal Disease in Children

PURPOSE OF REVIEW

This review summarizes the fungal diagnostic measures currently available for use in paediatric patients at high risk for developing invasive fungal disease (IFD) and those suspected of having an IFD. The clinical utility of each test is described based on reported performances of individual tests in specific paediatric populations.

RECENT FINDINGS

Available studies in the paediatric population are scarce and are characterized by a huge heterogeneity in underlying diseases (e.g. different risk for IFD), different study objectives and management strategies (screening versus diagnostic) used.

SUMMARY

A final valuation of paediatric studies on fungal diagnostic tools is limited. While the galactomannan and fungal PCR assays are useful to exclude the presence of IFD, it is unclear if mannan, mannan antibodies and β-D-glucan are of benefit due to a lack of studies or validation of the cut-off, respectively. Well-designed multicentre paediatric studies are urgently needed to improve the outcome of IFD.

PCR Technology for Detection of Invasive Aspergillosis

The application of molecular technologies to aid diagnosis and management of infectious diseases has had a major impact and many assays are in routine use. Diagnosis of aspergillosis has lagged behind. Lack of standardization and limited commercial interest have meant that PCR was not included in consensus diagnostic criteria for invasive fungal disease. In the last ten years careful evaluation and validation by the Aspergillus European PCR initiative with the development of standardized extraction, amplification and detection protocols for various specimen types, has provided the opportunity for clinical utility to be investigated. PCR has the potential to not only exclude a diagnosis of invasive aspergillosis but in combination with antigen testing may offer an approach for the early diagnosis and treatment of invasive aspergillosis in high-risk populations, with the added benefit of detection of genetic markers associated with antifungal resistance.

Galactomannan detection for invasive aspergillosis in immunocompromised patients

BACKGROUND

Invasive aspergillosis is the most common life-threatening opportunistic invasive mycosis in immunocompromised patients. A test for invasive aspergillosis should neither be too invasive nor too great a burden for the already weakened patient. The serum galactomannan enzyme-linked immunosorbent assay (ELISA) seems to have the potential to meet both requirements.

OBJECTIVES

To obtain summary estimates of the diagnostic accuracy of galactomannan detection in serum for the diagnosis of invasive aspergillosis.

SEARCH METHODS

We searched MEDLINE, EMBASE and Web of Science with both MeSH terms and text words for both aspergillosis and the sandwich ELISA. We checked the reference lists of included studies and review articles for additional studies. We conducted the searches in February 2014.

SELECTION CRITERIA

We included cross-sectional studies, case-control designs and consecutive series of patients assessing the diagnostic accuracy of galactomannan detection for the diagnosis of invasive aspergillosis in patients with neutropenia or patients whose neutrophils are functionally compromised. The reference standard was composed of the criteria given by the European Organization for Research and Treatment of Cancer (EORTC) and the Mycoses Study Group (MSG).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed quality and extracted data. We carried out meta-analysis using the bivariate method. We investigated sources of heterogeneity by adding potential sources of heterogeneity to the model as covariates.

MAIN RESULTS

We included 54 studies in the review (50 in the meta-analyses), containing 5660 patients, of whom 586 had proven or probable invasive aspergillosis. When using an optical density index (ODI) of 0.5 as a cut-off value, the sensitivity of the test was 82% (73% to 90%) and the specificity was 81% (72% to 90%). At a cut-off value of 1.0 ODI, the sensitivity was 72% (65% to 80%) and the specificity was 88% (84% to 92%). At a cut-off value of 1.5 ODI, the sensitivity was 61% (47% to 75%) and the specificity was 93% (89% to 97%). None of the potential sources of heterogeneity had a statistically significant effect on either sensitivity or specificity.

AUTHORS' CONCLUSIONS

If we used the test at a cut-off value of 0.5 ODI in a population of 100 patients with a disease prevalence of 9% (overall median prevalence), two patients who have invasive aspergillosis would be missed (sensitivity 82%, 18% false negatives), and 17 patients would be treated unnecessarily or referred unnecessarily for further testing (specificity 81%, 19% false negatives). If we used the test at a cut-off value of 1.5 in the same population, that would mean that four invasive aspergillosis patients would be missed (sensitivity 61%, 39% false negatives), and six patients would be treated or referred for further testing unnecessarily (specificity 93%, 7% false negatives). These numbers should, however, be interpreted with caution because the results were very heterogeneous.