Defining a case of invasive aspergillosis by serum galactomannan

[Detection of Aspergillus antigen galactomannan using ELISA method: validation of the performances of the method for accreditation]

Diagnosis of invasive aspergillosis for patients with high risk of infection is based on the monitoring of Aspergillus antigenemia assessed by the detection of galactomannan in serum by a sandwich-type ELISA (Biorad(®)). The validation of the method was displayed according to the guide COFRAC SH GTA 04. The internal quality control system settled, involves two quality control samples made of pools of sera (negative and positive). The repeatability of the measurements, as estimated by the coefficients of variation (CV), obtained by two different technicians was found from 9 to 13.7% for the positive control. The CV of the negative control, for which the provider indicates it is not useful in the analytical process, was found from 7.1 to 30%. In our experience it could be an indicator of environmental contamination. The evaluation of the intermediary fidelity was 15.7% for the positive control and 22.5% for the negative one. In the lack of reference material (International Standard) and recommendation from scientific societies, performances obtained will be discussed according to the results reported in the technical form of the supplier and those obtained by 39 laboratories participating in the only available external quality assessment program organized in France by ProBioQual(®) where the CV of reproducibility are 44.7% of unit (mean index 0.131) for the negative control and 18% (mean index 1.089) for the positive one in 2011.

Evaluation of serum galactomannan detection for diagnosis of feline upper respiratory tract aspergillosis

Measurement of serum galactomannan (GM), a polysaccharide fungal cell-wall component, is a non-invasive test for early diagnosis of invasive aspergillosis in humans. Feline upper respiratory tract (URT) aspergillosis is an emerging infectious disease in cats. Diagnosis requires biopsy for procurement of tissue specimens for cytological or histological detection of fungal hyphae and for fungal culture. The aim of this study was to evaluate serum GM measurement as a non-invasive diagnostic test for URT aspergillosis in cats. A one-stage, immunoenzymatic sandwich ELISA was used to detect serum GM in 4 groups of cats; Group 1 (URT aspergillosis) - confirmed URT aspergillosis (n=13, sinonasal aspergillosis (SNA) n=6 and sino-orbital aspergillosis (SOA) n=7), Group 2 (URT other) - other URT diseases (n=15), Group 3 (β-lactam) - cats treated with β-lactam antibiotics for non-respiratory tract disease (n=14), Group 4a - healthy young cats (≤ 1 y of age, n=28), Group 4b - healthy adult cats (>1 y of age, n=16). One cat with SNA and two cats with SOA caused by an Aspergillus fumigatus-mimetic species, tested positive for serum GM. For a cut-off optical density index of 1.5, the overall sensitivity and specificity of the assay was 23% and 78% respectively. False positive results occurred in 29% of cats in Group 3 and 32% of cats in Group 4a. Specificity increased to 90% when Groups 3 and 4a were excluded from the analysis. Overall, serum GM measurement has a poor sensitivity but is a moderately specific, non-invasive screening test to rule out infection in patients with suspected feline upper respiratory tract aspergillosis.

Neutropenic fever syndromes in patients undergoing cytotoxic therapy for acute leukemia and myelodysplastic syndromes

Fever represents the major surrogate of infection in neutropenic cancer patients. A number of neutropenic fever syndromes have been recognized, the causes and significance of which will vary depending upon the clinical context. First neutropenic fever syndromes are typically of bacterial origin, the character of which may be influenced by whether antibacterial chemoprophylaxis has been administered. Persistent neutropenic fevers are documented during the empirical systemic antibacterial therapy for the first neutropenic fever, the cause of which is likely outside the spectrum of activity of the initial therapy. Recrudescent neutropenic fevers, defined by the appearance of a new fever after defervescence of the first fever, are often a function of invasive fungal infection or gram-positive infections outside the spectrum of the initial empirical antibacterial regimen. The myeloid reconstitution syndrome occurs in parallel with neutrophil recovery from aplasia and may not necessarily represent new infection. Recognition of these patterns can help the clinician make better clinical judgments and management plans.

Considerations in the approach to invasive fungal infection in patients with haematological malignancies

Invasive infections because of opportunistic yeasts and moulds have contributed significantly to the morbidity and mortality associated with potentially curative treatment for haematological malignancies. Many risk factors have been identified that permit the clinician to predict the likelihood of these infections. The diagnostic process involves maintaining a high index of suspicion based upon an understanding of the clinical circumstances under which invasive fungal infections occur, of the spectrum of fungal syndromes, and of the advantages and limitations of diagnostic testing strategies now available. Treatment strategies may be categorized as prophylactic, pre-emptive, empiric, or directed based upon the circumstances. The therapeutic options have increased in recent years but are not applicable to all clinical circumstances. These considerations are discussed.

Estado actual del diagnóstico precoz de las infecciones invasoras causadas por Aspergillus y otros hongos filamentosos emergentes

The usefulness of surrogate markers in the diagnosis of invasive fungal infections caused by Aspergillus and other emerging mycelial fungi is based on the ability of surrogate markers to detect the infection caused by different species of mycelial fungi. Conventional microbiological methods for diagnosis of fungal disease are slow and insensitive. Antigen based assays or measurement of (1-3)-beta-D-glucan in blood have been developed and validated in clinical laboratories. We review these diagnostic contemporary tools, their clinical application and impact.

Update on the contribution of galactomannan for the diagnosis of invasive aspergillosis

The diagnosis of invasive fungal infections (IFI) remains a challenge, particularly for diseases caused by filamentous fungi such as Aspergillus species. Unfortunately, many patients affected by these conditions are not identified before autopsy. Therefore, there is a need for new diagnostic methods for IFI. Galactomannan is a soluble antigen released during hyphal growth in tissues. A commercially available sandwich ELISA assay that detects galactomannan has been used in Europe for many years and is now approved for use in the USA. The test has an excellent negative predictive value in the detection of invasive aspergillosis (IA) in high-risk patients. In addition, it is more sensitive than culture and allows IA to be diagnosed before clinical manifestations occur. However, false-negative and false-positive results in certain populations are the main limitations to its use. The purpose of this review is to summarize the current knowledge about galactomannan testing in patients at risk for IA.

Optimization of the cutoff value for the Aspergillus double-sandwich enzyme immunoassay

BACKGROUND

Many health care centers worldwide use the Platelia Aspergillus enzyme immunoassay (PA-EIA; Bio-Rad Laboratories) for diagnosis of invasive aspergillosis (IA). A cutoff optical density (OD) index of 1.5 was originally recommended by the manufacturer, but in practice, most institutions use lower cutoff values. Moreover, a cutoff OD index of 0.5 was recently approved in the United States. In the present study, we set out to optimize the cutoff level by performing a retrospective analysis of PA-EIA values for samples that had been obtained prospectively from adult patients at risk for IA at 2 European health care centers.

METHODS

In total, 239 treatment episodes were included of which there were 19 episodes of proven IA and 19 episodes of probable IA. Per-episode and per-test analyses and receiver operating characteristic curves were used to determine the optimal cutoff value.

RESULTS

In the per-episode analysis, lowering the cutoff OD index for positivity from 1.5 to 0.5 increased the overall sensitivity by 21% (from 76.3% to 97.4%) but decreased the overall specificity by 7% (from 97.5% to 90.5%). Requiring 2 consecutive samples with an OD index > or = 0.5 resulted in the highest test accuracy, with an improved positive predictive value. At a cutoff OD index of 0.5, the antigen test result was positive during the week before conventional diagnosis in 65% of cases and during the week of diagnosis in 79.5% of cases.

CONCLUSIONS

A cutoff OD index of 0.5--identical to the approved cutoff in the United States--improves the overall performance of the PA-EIA for adult hematology patients.