Value of antigen detection using an enzyme immunoassay in the diagnosis and prediction of invasive aspergillosis in two adult and pediatric hematology units during a 4-year prospective study

Evaluation of a (1->3)-beta-D-glucan assay for diagnosis of invasive fungal infections

The Fungitell assay (Associates of Cape Cod, Inc.) is a commercial test that detects (1-3)-beta-D-glucan (BG) and is intended for diagnosis of invasive fungal infections. To evaluate the Fungitell assay, we tested serum and plasma samples from healthy blood donors and from patients with blood cultures positive for yeast or bacteria. All 36 blood donors were BG negative, and 13 of 15 candidemic patients were BG positive. Of 25 bacteremic patients, 14 (10 with gram-positive bacteremia) were BG positive. One of the latter patients with Staphylococcus aureus bacteremia also had invasive candidiasis, based on histological findings in a tissue biopsy; therefore, the BG result was a true positive. The sensitivity, specificity, and positive and negative predictive values of the Fungitell assay, by patient, for these three groups were 93.3%, 77.2%, 51.9%, and 97.8%, respectively. We also performed the Fungitell assay on sera that had been tested for Aspergillus galactomannan or Histoplasma antigen. All six Histoplasma antigen-positive patients and 31 of 32 Aspergillus galactomannan-positive patients were also BG positive. BG results for the 10 Histoplasma antigen-negative and the 32 Aspergillus galactomannan-negative patients varied, but we were unable to confirm many of the results. Between-run coefficients of variance (CVs) for the assay ranged from 3.2% to 16.8%; within-run CVs were < or =4.8%. The correlation coefficient for an interlaboratory reproducibility study was 0.9892. Concentrations of hemoglobulin, bilirubin, and triglycerides that caused 20% interference were 588, 72, and 466 mg/dl, respectively. Our results suggest that the Fungitel assay may be most useful for excluding invasive fungal infection.

Early diagnosis of invasive aspergillosis in infants and children

Effective management of invasive aspergillosis (IA) requires early and accurate diagnosis. Microscopy and culture of appropriate specimens remain the gold standard of mycological diagnosis. High-resolution computed tomography serially performed constitutes a sensitive mode of diagnosis of pulmonary IA in hematological patients, but similar data is lacking for children. While early diagnosis of IA has been improved with galactomannan assay in adults, its use is problematic in young infants due to specificity inferiority. Galactomannan testing also is characterized by low sensitivity in pediatric patients with primary immunodeficiencies including chronic granulomatous disease and Job's syndrome. Beta-D glucan assay has been studied in adult patients with fungal infections including IA. The high negative predictive value of the assay allows its use for excluding IA; no specific data, however, exist for children. Polymerase chain reaction (PCR) may be a powerful tool for early diagnosis of IA but has not been standardized for routine use yet. No studies address the issue in neonates, whereas in children PCR has not been specifically studied but is probably as good as in adults. A high degree of suspicion in immunodeficient pediatric hosts, suggestive clinical and radiological findings, as well as mycological data by application of multiple diagnostic methods including serology and molecular biology, are expected to enhance the capacity to diagnose IA in young patients.

Aspergillus pulmonary infections in transplant recipients

Aspergillus infections are increasing in frequency in those undergoing solid organ and hematopoietic stem cell transplantation. The ongoing impact of Aspergillus infection on morbidity and mortality after transplantation makes this subject an area of intense clinical and research interest. This article discusses the evolving epidemiologic features of the infection and its management and diagnosis.

Detection of Aspergillus galactomannan antigenemia to determine biological and clinical implications of beta-lactam treatments

Detection of Aspergillus galactomannan (GM) in serum with the Platelia Aspergillus enzyme immunoassay (EIA) is useful for diagnosing invasive aspergillosis. From May 2003 to November 2004, 65 patients who did not develop aspergillosis had at least two positive sera while receiving a beta-lactam treatment (GM index [GMI], >or=0.5). Of the 69 treatment episodes scored, 41 consisted of a beta-lactam other than piperacillin-tazobactam (n=29), namely, amoxicillin-clavulanate (n=25), amoxicillin (n=10), ampicillin (n=3), or phenoxymethylpenicillin (n=2). In all cases, antigenemia became negative 24 h to 120 h upon stopping the antibiotic. Monitoring of 35 patients, including 26 with hematological malignancies, revealed three antigenemia kinetic patterns: each was observed with any drug regimen and consisted of a persistent GMI of >2.0 (65.7%), >0.5, and <or=1.5 (25.7%) or a variable GMI (14.3%) from the onset of antibiotic therapy. All available drug batches given to 26 patients cross-reacted with the EIA. Galactomannan titration in batches failed to predict the GM titers in the five patients studied at cumulative doses of ampicillin or amoxicillin-clavulanate, regardless of the time lapse between serum sampling and infusion period. Our results show that beta-lactams other than piperacillin-tazobactam may lead to false presumption of aspergillosis. The resulting kinetic patterns of GM antigenemia are variable, and sampling serum prior to the next beta-lactam dose may not decrease GMI below the threshold. Consequently, testing of suspected antibiotic batches remains the only indicator of possible false EIA positivity.

Comparison of galactomannan detection, PCR-enzyme-linked immunosorbent assay, and real-time PCR for diagnosis of invasive aspergillosis in a neutropenic rat model and effect of caspofungin acetate

The performance of different in vitro diagnostic tests for the diagnosis of invasive aspergillosis (IA) was investigated in a transiently neutropenic rat model. Rats were immunosuppressed with cyclophosphamide and then inoculated intravenously with 1.5 x 10(4) CFU Aspergillus fumigatus spores. Animals were then either treated with caspofungin acetate, 1 mg/kg/day for 7 days, or not treated. PCR-enzyme-linked immunosorbent assay (ELISA), real-time PCR, and galactomannan (GM) detection were performed on postmortem blood samples, along with culture of liver, lung, and kidney homogenate. Caspofungin-treated animals showed a decrease in residual tissue burden of A. fumigatus from organ homogenate compared to untreated animals (P < 0.002). PCR-ELISA returned positive results for 11/17 animals treated with antifungal agents and for 10/17 untreated animals. Galactomannan was positive in 8/17 caspofungin-treated animals and 4/17 untreated animals. Real-time PCR was positive in 2/17 treated and 3/17 untreated animals. This study demonstrates that PCR-ELISA is a more sensitive test than either GM detection (P = 0.052) or real-time PCR (P < 0.01) for diagnosis of IA but that any of the three tests may return false-negative results in cases of histologically proven disease. Galactomannan indices from animals treated with antifungal agents showed a trend (P = 0.1) towards higher levels than those of untreated animals, but no effect was observed with PCR-ELISA indices (P = 0.29). GM detection, as previously described, may be enhanced by the administration of caspofungin, but PCR-ELISA appears not to be affected in the same way. We conclude that PCR-ELISA is a more sensitive and reliable method for laboratory diagnosis of IA.

Reproducibility of low galactomannan enzyme immunoassay index values tested in multiple laboratories

The Platelia galactomannan enzyme immunoassay is a commercially available nonculture method for diagnosing invasive aspergillosis. Recently, steps have been taken to improve sensitivity; specifically, a low (0.5 to 0.7) galactomannan index (GMI) value to determine positivity has been validated by multiple groups. We evaluated the intra-assay and interassay reproducibility at low index levels using three different kit lots on three different days in three different microbiology laboratories. Clinical and spiked sera were blinded and sent with galactomannan enzyme immunoassay (EIA) kits to the participating laboratories. We also prospectively collected data on all galactomannan EIAs performed between 1 September 2003 and 21 July 2004 at the University of Washington Medical Center microbiology laboratory to assess reproducibility of clinical samples analyzed in "real time." From the multilaboratory study, a total of 836 results were available for evaluation. Reproducibility was excellent between laboratories and on different days. Significant variability was seen between runs/lots, which may in part be associated with different threshold control values in different kits. Among the 1,410 clinical samples that were prospectively analyzed, 168 (90%) were confirmed to be positive on repeat testing (GMI, > or =0.5). Among the 19 (10.2%) initially positive samples not confirmed on repeat testing, the majority had a GMI at the threshold of the assay (between 0.5 and 0.7). Our findings suggest that the Platelia galactomannan immunoassay has good reproducibility. However, changes in GMI levels when different kit lots are used, and single samples with low-positive (GMI of 0.5 to 0.7) indices, should be interpreted with caution.

Galactomannan and computed tomography-based preemptive antifungal therapy in neutropenic patients at high risk for invasive fungal infection: a prospective feasibility study

BACKGROUND

Empirical antifungal therapy is the standard treatment for persistent or relapsing antibiotic-resistant neutropenic fever. However, overtreatment resulting in increased toxicity and treatment-related cost is a major shortcoming of such therapy. We assessed the feasibility of a "preemptive" approach based on the incorporation of sensitive, noninvasive diagnostic tests for consecutive high-risk neutropenic patients who had received fluconazole prophylaxis while avoiding empirical therapy.

METHODS

A total of 136 treatment episodes for persons who were at risk of acquiring invasive fungal infection (IFI) were screened for the presence of galactomannan with an enzyme immunoassay. A diagnostic evaluation, which included thoracic computed tomography scanning (HRCT) and bronchoscopy with lavage, was performed on the basis of well-defined clinical, radiological, and microbiological criteria. Only seropositive patients and patients with a positive microbiological test result plus supportive radiological findings received liposomal amphotericin B.

RESULTS

Neutropenic fever developed in 117 episodes, of which at least 41 episodes (35%) satisfied existing criteria for empirical antifungal therapy. However, our protocol-driven preemptive approach reduced the rate of antifungal use for these episodes from 35% to 7.7% (a 78% reduction) and led to the early initiation of antifungal therapy in 10 episodes (7.3%) that were clinically not suspected of being IFI. No undetected cases of invasive aspergillosis were identified; 1 case of zygomycosis was missed. Breakthrough candidemia was diagnosed by conventional culture techniques and was treated successfully. With use of a preemptive approach, the 12-week survival rate for patients with IFI was 63.6% (it was 63.1% for those with invasive aspergillosis).

CONCLUSION

Preemptive therapy based on enzyme immunoassay and HRCT reduced the exposure to expensive and potentially toxic drugs and offered effective antifungal control, but it failed to detect non-Aspergillus IFI.

Bifidobacterial lipoglycan as a new cause for false-positive platelia Aspergillus enzyme-linked immunosorbent assay reactivity

We previously hypothesized that a lipoglycan of Bifidobacterium bifidum subsp. pennsylvanicum cross-reacts with the Platelia Aspergillus (PA) enzyme-linked immunosorbent assay (ELISA) based on the presence of galactofuranosyl epitopes in the cell wall (M. A. S. H. Mennink-Kersten, R. R. Klont, A. Warris, H. J. M. Op den Camp, and P. E. Verweij, Lancet 363:325-327, 2004). We tested this hypothesis by testing bacterial suspensions of different bifidobacterial species and other gram-positive and -negative bacteria with the PA ELISA, which is used to detect circulating galactomannan for the serodiagnosis of invasive aspergillosis. Furthermore, neonatal fecal samples were enumerated for bifidobacteria by fluorescence in situ hybridization (FISH) and tested for PA ELISA reactivity. All bifidobacteria, except B. infantis and B. adolescentis, showed reactivity 6- to 600-fold higher compared to the controls (i.e., Micrococcus luteus and Propionibacterium freudenreichii, which contain a cell wall lipomannan). Eggerthella lenta showed a 25-fold-higher reactivity. ELISA reactivity was clearly shown to be associated with bacterial lipoglycans containing a beta-1,5-galactofuranosyl chain. All neonatal feces showed PA ELISA reactivity and associated numbers of bifidobacteria. Since high concentrations of bifidobacteria are present in the human gut, these bacteria or excreted lipoglycan may cause false serum PA ELISA reactivity in selected patient groups, especially neonates.

Design Issues in Studies Evaluating Diagnostic Tests for Aspergillosis

Although invasive aspergillosis is recognized as an increased concern for immunosuppressed patients, establishing an early diagnosis remains a challenge. Current methods for diagnosis, including sensitive radiography and invasive procedures to identify organisms in affected tissues, provide an early diagnosis for only a small proportion of patients infected with Aspergillus species. The availability of a standardized assay to detect circulating Aspergillus galactomannan, the BioRad Platelia Aspergillus galactomannan enzyme immunoassay, should be considered as a valuable tool. However, at present, clinical utility is hampered by controversies surrounding the performance of the test and an apparent lack of definitive data. These controversies emphasize the complexity inherent in analyzing diagnostic tests for aspergillosis. The widespread availability of a standardized assay may now allow us to address the multiple sources of variability and bias via large, cooperative studies.

Value of measuring serum procalcitonin, C-reactive protein, and mannan antigens to distinguish fungal from bacterial infections

The study presented here was conducted to determine the diagnostic value of measuring procalcitonin, C-reactive protein, and mannan antigens to distinguish fungal from bacterial infections. The sensitivity and specificity of these measurements ranged from 35% to 97%. On days 1 and 3 following the onset of fever, both serum procalcitonin and C-reactive protein levels were lower in patients with fungal infections than in those with bacterial infections (p<0.0001). The presence of mannan antigens combined with a procalcitonin level <0.5 ng/ml provided higher specificity for distinguishing fungal from bacterial infections than each result alone.

Galactomannoproteins of Aspergillus fumigatus

Galactofuranose-containing molecules have been repeatedly shown to be important antigens among human fungal pathogens, including Aspergillus fumigatus. Immunogenic galactofuran determinants have been poorly characterized chemically, however. We reported here the characterization of two glycoproteins of A. fumigatus with an N-glycan containing galactofuranose. These proteins are a phospholipase C and a phytase. Chemical characterization of the N-glycan indicates that it is a mixture of Hex(5-13)HexNAc(2) oligosaccharides, the major molecular species corresponding to Hex(6-8)HexNAc(2). The N-glycan contained one galactofuranose unit that was in a terminal nonreducing position attached to the 2 position of Man. This single terminal nonreducing galactofuranose is essential for the immunoreactivity of the N-glycans assessed either with a monoclonal antibody that recognizes a tetra-beta-1,5-galactofuran chain of galactomannan or with Aspergillus-infected patient sera.

The contribution of galactomannan detection in the diagnosis of invasive aspergillosis in bone marrow transplant recipients

Until recently, accurate microbiological diagnosis of invasive aspergillosis (IA) was seldom established in HSCT recipients. Blood samples are rarely positive for Aspergillus species, the reliability of the cultures depends of the specimen (if taken from a normally sterile site or not) and biopsy samples require invasive procedures, rarely recommended in patients with severe thrombocytopenia. Implementing the international consensus defining the microbiological criteria for the diagnosis of Aspergillus infection, we retrospectively evaluated the role of serum galactomannan (GM) detection by EIA to diagnose IA among HSCT patients with proven invasive fungal infection (IFI) and the impact of serum storage in GM concentrations. The EIA assay allowed categorizing as "probable" 5 of the 10 cases of "possible" aspergillosis (50%). Considering a lower cut-off level for the reaction (1.0), 80% of the cases could be categorized as "probable" aspergillosis. Positive or undetermined results were detected one to 4 months before the diagnosis of IA in eight of the 11 patients (72.7%) with proven IFI. Retesting the stored samples after a second storage for four years, we could observe lower reactivity in 20% of the samples. The detection of galactomannan by the EIA test represents a major advance in the diagnosis of IA in HSCT recipients at high risk of IA. A better understanding of the kinetics of the GM in different clinical situations is necessary to maximize the benefit of the test in Aspergillus surveillance.

Evaluation of serum sandwich enzyme-linked immunosorbent assay for circulating galactomannan during caspofungin therapy: results from the caspofungin invasive aspergillosis study

There has been minimal clinical experience with the use of the Aspergillus galactomannan enzyme-linked immunosorbent assay (ELISA) for patients receiving echinocandin therapy. We reviewed the experience with the galactomannan ELISA for 17 patients in a study of caspofungin treatment for invasive aspergillosis. The rate of successful outcomes for these patients was similar to that overall for participants in the study. Trends in antigenemia levels correlated with clinical and radiographic findings.

Contribution of (1->3)-beta-D-glucan chromogenic assay to diagnosis and therapeutic monitoring of invasive aspergillosis in neutropenic adult patients: a comparison with serial screening for circulating galactomannan

Two noninvasive diagnostic tests, (1-->3)-beta-D-glucan (BG) (Glucatell) and galactomannan (GM) (Platelia Aspergillus), were used retrospectively in a twice-weekly screening for the diagnosis of invasive aspergillosis (IA) in 40 treatment episodes (one hospital visit per patient) in 40 neutropenic adult patients at high risk for IA. Five proven IA cases, three probable IA cases, and three possible IA cases were diagnosed. Diagnostic levels of both BG and GM were detected in 100% of patients with proven IA cases and in 66% of patients with probable IA cases. The kinetics of both markers in patients with IA were similar. The sensitivity, specificity, and positive and negative predictive values for GM and BG were identical, namely, 87.5, 89.6, 70, and 96.3%, respectively. False-positive reactions occurred at a rate of 10.3% in both tests, but the patients showing false-positive results were different in each test. Both tests anticipated the clinical diagnosis, computed tomography abnormalities, and the initiation of antifungal therapy in most patients, but BG tended to become positive earlier than GM. A combination of the two tests improved the specificity (to 100%) and positive predictive value (to 100%) of each individual test without affecting the sensitivity and negative predictive values. In conclusion, BG and GM detection are useful tests for the diagnosis of IA in high-risk hematological patients, but a combination of the two tests was very useful to identify false-positive reactions by each test.

[Antigen detection in invasive aspergillosis and candidosis: the Austrian experience]

In order to assess the performance of different methods for the detection of fungal antigens, data of five Austrian hospitals were evaluated. The enzyme immunoassay (EIA) Platelia Aspergillus Antigen (Bio-Rad, USA) was used for the diagnosis of invasive aspergillosis and compared with clinical data. It could be shown that it is more effective to investigate at least two sequential sera than only one sole serum. For several high-risk patients diagnosis could be improved or confirmed by investigating other body fluids such as cerebrospinal fluid or bronchoalveolar lavage fluid in addition to sera. For invasive Candida infections several diagnostic kits detecting antigens are commercially available. The performance of the EIA Platelia Candida Antigen (Bio-Rad, USA), the latexagglutination test Cand-Tec (Ramco, USA) and the detection of (1-3)-Beta-D-Glucan using the test kit Glucatell (CAPE COD, USA) were evaluated. The detection of (1-3)-Beta-D-Glucan by means of Glucatell showed the highest sensitivity as all sera of 15 patients with invasive candidosis showed positive results. The other tests showed positive and negative results independently of the occurrence of an invasive infection. However, the number of tested sera is too small to decide which test is the most appropriate for establishing an early and definite diagnosis. Prospective studies in combination with clinical data are still needed for definite evaluation.

A prospective study of real-time panfungal PCR for the early diagnosis of invasive fungal infection in haemato-oncology patients

A blinded prospective study was performed to determine whether screening of whole blood using a real-time, panfungal polymerase chain reaction (PCR) technique could predict the development of invasive fungal infection (IFI) in immunocompromised haemato-oncology patients. In all, 78 patients (125 treatment episodes) were screened twice weekly by real-time panfungal PCR using LightCyclertrade mark technology. IFI was documented in 19 treatment episodes (five proven, three probable and 11 possible), and in 12, PCR was sequentially positive. PCR positivity occurred in: 4/5 proven; 2/3 probable; 6/11 possible; and 29/106 with no IFI. In 8/12 with IFI and sequentially positive PCR results, PCR positivity occurred before (median 19.5 days) and in 4/12 (median 10.5 days) after the initiation of empirical antifungal therapy. Based on sequential positive results for proven/probable IFI sensitivity, specificity, positive predictive value and negative predictive value were 75, 70, 15 and 98%, respectively. Real-time panfungal PCR is a sensitive tool for the early diagnosis of IFI in immunocompromised haemato-oncology patients. It may be most useful as a screening method in high-risk patients, either to direct early pre-emptive antifungal therapy or to determine when empirical antifungal therapy can be withheld in patients with antibiotic--resistant neutropenic fever. However, these strategies require further assessment in comparative clinical trials.

Application of nucleic acid sequence-based amplification for diagnosis of and monitoring the clinical course of invasive aspergillosis in patients with hematologic diseases

BACKGROUND AND METHODS

We evaluated nucleic acid sequence-based amplification (NASBA) and a galactomannan enzyme immunosorbent assay (GM-EIA) for the diagnosis of invasive aspergillosis (IA) in neutropenic febrile patients and for monitoring of its clinical course and outcome. Blood samples were collected twice per week from 128 patients with hematologic diseases during periods of neutropenic fever after undergoing chemotherapy or hematopoietic stem cell transplantation. A total of 448 blood samples were tested.

RESULTS

There were 14 patients with IA (2 patients with proven IA and 12 with probable IA). The median index of the initial NASBA in the IA group was more than 10-fold higher than that in the non-IA group. Galactomannan antigenemia (index, >0.5) was detected with a sensitivity of 86%. In receiver-operator characteristic analysis, the cutoff index of NASBA for the presumptive diagnosis of IA was determined to be 5.0. Combination of these 2 parameters (either a GM-EIA index of >or=0.5 or a NASBA index of >or=5.0) improved the sensitivity of diagnosis to 100%. There was a close relationship between patient outcome and the kinetics of NASBA values: failure of negative conversion during treatment resulted in death in almost all cases.

CONCLUSION

If either GM-EIA or NASBA results suggest IA, the diagnostic yield for IA could be improved, and NASBA could be a useful marker for predicting the clinical course and outcome of treatment.

Aspergillus infections in transplant recipients

Aspergillus infections are occurring with an increasing frequency in transplant recipients. Notable changes in the epidemiologic characteristics of this infection have occurred; these include a change in risk factors and later onset of infection. Management of invasive aspergillosis continues to be challenging, and the mortality rate, despite the use of newer antifungal agents, remains unacceptably high. Performing molecular studies to discern new targets for antifungal activity, identifying signaling pathways that may be amenable to immunologic interventions, assessing combination regimens of antifungal agents or combining antifungal agents with modulation of the host defense mechanisms, and devising diagnostic assays that can rapidly and reliably diagnose infections represent areas for future investigations that may lead to further improvement in outcomes.

Utility of Aspergillus Antigen Detection in Specimens Other than Serum Specimens

The detection of circulating galactomannan in serum is an important tool for the early diagnosis of invasive aspergillosis. A commercial enzyme-linked immunosorbent assay (Platelia Aspergillus; BioRad) was shown to be both highly sensitive and specific for detection of galactomannan in serum samples. Despite the fact that this assay is validated for serum samples, specimens of other body fluids are increasingly used for detection of galactomannan, including urine, bronchoalveolar lavage fluid, and cerebrospinal fluid. Review of the literature shows that galactomannan can be detected in each of these samples from patients with invasive aspergillosis with higher sensitivity than is the case with culture, as well as early in the course of infection. However, the evidence thus far is based on case reports--predominantly retrospective studies--that often include heterogeneous patient populations and limited numbers of cases of proven infection. Clearly, well-designed prospective studies with systematic sampling and use of consensus case definitions are needed to compare the performance of antigen detection in samples other than serum specimens with that in serum specimens.

Advances in the molecular and serological diagnosis of invasive fungal infection in haemato-oncology patients

Current laboratory diagnostic methods for invasive fungal infection (IFI) in haemato-oncology patients are insensitive, resulting in late diagnosis and contributing to high mortality. In recent years, progress has been made in the development and evaluation of sensitive sero-diagnostic assays, including detection of genomic DNA sequences and fungal antigens, which aid in a rapid, early diagnosis of IFI. The sensitivity and specificity of the assays vary considerably between studies, highlighting the need to correlate serological results with conventional laboratory tests and clinical or radiological findings. As part of management protocols, these assays may help to confirm the diagnosis of suspected IFI; however, the impact on mortality from IFI may be greatest when they are used to screen high-risk patients. Persistently positive screening results could direct early aggressive antifungal therapy, guided further by radiological and microbiological findings combined with regular clinical review, while the excellent negative predictive value may allow treatment to be withheld in patients with antibiotic resistant neutropenic fever but no other signs of IFI. However, this pre-emptive approach requires evaluation in prospective randomized trials.

Prospective clinical evaluation of lower cut-offs for galactomannan detection in adult neutropenic cancer patients and haematological stem cell transplant recipients

The recent advent of an improved commercial serum enzyme-linked immunosorbent assay (ELISA) for the detection of circulating galactomannan (GM), a major constituent of Aspergillus cell walls, has contributed to the diagnosis of invasive aspergillosis (IA) in many haematology and transplant centres. However, the optimal threshold for positivity remains a matter of debate. We prospectively evaluated the impact of lowering the cut-off in 124 neutropenic episodes with a high pretest probability for IA. Two new cut-off points, lower than previously accepted, are proposed: (a) a 'static' cut-off at 0.8 and (b) a 'dynamic' cut-off at 0.5. A single assay with an optical density (OD) index > or = 0.8 warrants the initiation of anti-Aspergillus therapy. A further lowering of the 'static' threshold seems not clinically feasible given the drop in positive predictive value (PPV). However, the demonstration of at least two sequential sera with an OD > or = 0.5 ('dynamic' threshold) increased the specificity and the PPV to 98.6% and the efficiency to 98%. Applying both cut-offs to a subgroup of 21 'possible' fungal infections further identified and upgraded six cases of IA. However, the clinical benefit of lower cut-offs (particularly for earlier diagnosis) depends upon the kinetics of antigenaemia and the intensity of serum sampling.

Choices aplenty: antifungal prophylaxis in hematopoietic stem cell transplant recipients

The incidence of invasive fungal infection (IFIs) in hematopoietic stem cell transplantation (HSCT) recipients ranges from 10 to 25% with an overall case fatality rate of up to 70-90%. Candida and Aspergillus genera remain the two most common pathogens. Although fluconazole prophylaxis in this population has been moderately effective in reducing mortality due to invasive candidiasis, this agent does not have activity against invasive aspergillosis (IA) and other mould. Several new agents such as voriconazole and caspofungin have enhanced potency and broad-spectrum antifungal activity and show promising results against yeasts and filamentous fungi when given as therapy and as chemoprophylaxis. Further, new diagnostic tools to detect circulating fungal antigens in biological fluids and PCR-based methods to detect species or genus-specific DNA or RNA have been developed. Incorporating these techniques along with clinical criteria appear to improve the accuracy of preclinical diagnosis of IFIs. Such approaches may alter the current treatment strategy from prophylaxis to pre-emptive therapy, thereby potentially decreasing cost and toxicity in high-risk patients.

Detection of circulating galactomannan for the diagnosis and management of invasive aspergillosis

The availability of the Platelia Aspergillus, a sandwich ELISA kit that detects circulating galactomannan, has been a major advance for managing patients at risk for invasive aspergillosis because of the early detection of the antigen. The assay is now widely used throughout the world, including the USA. Although initial studies that assessed the performance characteristics of this assay reported high sensitivity and specificity, more recent studies show significant variation in performance. The causes of this variability are multifactorial and, in large part, cannot be explained because there is insufficient understanding of the kinetics of galactomannan in vivo. We explored some of the factors that affect the release of the aspergillus antigen that bears the epitope that reacts with the monoclonal antibody used in the ELISA, its leakage from the site of infection into the blood, and its binding to substances present in the blood. Factors that affect the detection of antigen in blood are also discussed, most notably the pretreatment procedure aimed at liberating the antigen from immune complexes. Understanding the biology of galactomannan release by aspergillus will greatly enhance our understanding of the kinetics of this and other surrogate markers and allow their optimum use in the management of invasive aspergillosis.

Impact of diagnostic markers on early antifungal therapy

PURPOSE OF REVIEW

The early treatment of invasive fungal infection is critical but is hampered by the non-specific nature of clinical and radiological signs and the insensitivity of current laboratory diagnostic methods. If mortality due to invasive fungal infection is to be reduced, new, preemptive therapeutic strategies, targeting those patients at highest risk, are required and these will depend on the development of rapid, sensitive diagnostic methods. Such methods have become available in the form of high-resolution computed tomography scanning and serological and molecular techniques and in this review the authors describe recent studies assessing the utility of these methods and consider their role in management strategies.

RECENT FINDINGS

Sensitive assays for the detection of fungal DNA and antigens such as galactomannan and glucan have been prospectively evaluated in the clinical setting and enable identification of patients at an earlier stage of infection. However, the sensitivity and specificity of the assays vary considerably in different studies, depending on several factors including patient selection and clinical application of the test, and issues regarding the release and circulation of galactomannan and fungal DNA remain to be clarified.

SUMMARY

Rapid serological and molecular diagnostic methods facilitate the early diagnosis of invasive fungal infection and would appear to be most useful when used prospectively to screen high-risk patients. However, in order to determine the optimal approach to treatment it is essential that these tests are incorporated into management strategies and their impact on incidence of invasive fungal infection and clinical outcome evaluated in further clinical trials.

Prospective assessment of Platelia Aspergillus galactomannan antigen for the diagnosis of invasive aspergillosis in lung transplant recipients

The clinical utility of Platelia trade mark Aspergillus galactomannan antigen for the early diagnosis of invasive aspergillosis was prospectively assessed in 70 consecutive lung transplant recipients. Sera were collected twice weekly and tested for galactomannan. Invasive aspergillosis was documented in 17.1% (12/70) of the patients. Using the generalized estimating equation model, at the cutoff value of >or= 0.5, the sensitivity of the test was 30%, specificity 93% with positive and negative likelihood ratios of 4.2 and 0.75, respectively. Increasing the cutoff value to >or= 0.66 yielded a sensitivity of 30%, specificity of 95%, and positive and negative likelihood ratios of 5.5 and 0.74. A total of 14 patients had false-positive tests, including nine who had cystic fibrosis or chronic obstructive pulmonary disease. False-positive tests occurred within 3 days of transplantation in 43% (6/14) of the patients, and within 7 days in 64% (9/14). Thus, the test demonstrated excellent specificity, but a low sensitivity for the diagnosis of aspergillosis in this patient population. Patients with cystic fibrosis or chronic obstructive pulmonary disease may transiently have a positive test in the early post-transplant period.

Development of a serum-based Taqman real-time PCR assay for diagnosis of invasive aspergillosis

We compared an Aspergillus fumigatus-specific Taqman real-time PCR assay for the diagnosis of invasive aspergillosis (IA) with the enzyme-linked immunosorbent assay Platelia Aspergillus method. Patients with proven or probable IA had positive results with at least one of the two methods. The PCR method seems to be more specific, and a combination of the two should improve the diagnosis of IA.

New options for the treatment of invasive fungal infections

Fungal infections continue to plague patients undergoing treatment of malignancies. In fact, the incidence as well as the types of fungal species causing serious invasive fungal infections is increasing. Candida infections have become the fourth leading cause of nosocomial blood stream infections. Moreover, in addition to Aspergillus, non-Aspergillus species have emerged as etiologic agents of mold infections in cancer patients. Recently, there have been new and much needed re-enforcements to the antifungal armamentarium. These include the broader triazole antifungal agents that are in clinical trials (posaconazole) or have been recently approved (voriconazole) and the echinocandins, a new antifungal class of which the first approved agent caspofungin is now available. We review the clinical data, side effects, drug interactions, and unique spectrum of activity of these newer antifungal agents against both Candida and clinically relevant mold species.

Treatment with Piperacillin‐Tazobactam and False‐PositiveAspergillusGalactomannan Antigen Test Results for Patients with Hematological Malignancies

We report the occurrence of a high rate of false-positive test results during the surveillance of hematology patients for galactomannan (GM) antigenemia. Among 218 patients surveyed from June 2002 through June 2003, 42 (19.3%) had > or =1 serum sample positive for GM (optical density index, >1.5). Of these patients, 38 had no additional evidence of invasive aspergillosis, and, therefore, their test results were considered to be false-positives. Case-control analysis showed that treatment with piperacillin-tazobactam was the only risk factor significantly associated with receiving false-positive test results. When tested for GM antigen, 3 of 4 piperacillin-tazobactam batches had positive results. Physicians should be aware of the possible interference of treatment with piperacillin-tazobactam when interpreting the results of the GM assay.

False-positive galactomannan platelia Aspergillus test results for patients receiving piperacillin-tazobactam

At the bone marrow transplantation center of the San Martino Hospital (Genoa), we observed an increase in the rate of patients with positive Platelia Aspergillus (PA; Bio-Rad) test results, from 10% (38 of 386 patients) in the period from January 1999 through January 2003 to 36% (21 of 59 patients) in the period from February 2003 through May 2003. Positivity was significantly (P<.001) associated with the administration of piperacillin-tazobactam (PT) (17 [74%] of 23 patients who received PT had positive results vs. 4 [11%] of 36 who did not receive PT). Multivariate analysis found administration of PT ( chi 2=34.7; P<.001) and underlying disease ( chi 2=21.14; P<.001) to be associated with PA positivity. Of 15 PT batches tested, 12 had positive PA test results.

Bifidobacterium lipoteichoic acid and false ELISA reactivity in aspergillus antigen detection

A major difficulty with the detection of circulating galactomannan, a cell-wall polysaccharide released by Aspergillus sp during growth, in the serodiagnosis of invasive aspergillosis is the occurrence of false-positive ELISA results, especially in neonates and infants. On the basis of molecule similarity, we postulate that a lipoteichoic acid of Bifidobacterium sp can act as epitope for the monoclonal antibody used in the ELISA. The neonatal gut is heavily colonised with Bifidobacterium sp and these bacteria or their lipoteichoic acid might cause ELISA reactivity with serum after translocation because of immaturity of the intestinal mucosa. If our hypothesis is correct, we might find a method to discriminate between false-positive and true-positive ELISA results and thereby prevent unnecessary pre-emptive treatment of patients.

Recomendaciones para el diagnóstico micológico y estudios de sensibilidad a los antifúngicos

The guidelines presented herein, which are based on the indications established by various studies and expert opinions, analyze several issues related to laboratory diagnosis of invasive fungal infections in immunosuppressed patients.

Infectious complications following nonmyeloablative allogeneic hematopoietic stem cell transplantation

Nonmyeloablative hematopoietic stem cell transplantation (NST) has been explored in hematological malignancies and solid tumors in an attempt to minimize treatment-related toxicity. Whether this approach is associated with reduced risk of infectious complications is unclear. The aim of the current study was to evaluate the infectious complications in a series of 32 consecutive adult patients who received NST at our institution. Peripheral blood stem cell grafts (n=30) or marrow grafts (n=2) were infused from human leukocyte antibody (HLA)-matched sibling (n=30), partially matched related (n=1), or unrelated (n=1) donors. Neutropenia developed in two-thirds of patients and lasted 16 days. Acute graft-versus-host disease (GVHD) grade II to IV was observed in 25% of patients, whereas 35% of patients had signs of extensive chronic GVHD. Twenty-two patients (69%) had at least one significant infectious episode. Bacteremia occurred in 19% of patients (n=5 gram-positive, n=1 gram-negative microorganisms). Cytomegalovirus (CMV) infection was observed in 10 out of 28 (36%) evaluable patients; 4 of these had recurrent or persistent CMV antigenemia requiring a second-line treatment, but eventually the viremia cleared. No patients experienced CMV disease. Fungal infections were documented in five (16%) patients, comprising invasive fungal infections in two cases and mucosal fungal infections in three. Four patients died of transplant-related causes, and three of these died before day +100. Infection was considered the primary cause of death in one patient (pulmonary aspergillosis) and contributed to death in another two. The actuarial probability of nonrelapse mortality at 100 days was 10% (95% confidence interval, 3-26%). Our preliminary results suggest that NST is associated to a low incidence of bacteremia or fungal and viral infections. Whether these findings would translate into an improved overall survival needs to be confirmed in larger prospective studies.

Galactomannan detection in computerized tomography-based broncho-alveolar lavage fluid and serum in haematological patients at risk for invasive pulmonary aspergillosis

We determined the value of galactomannan (GM) detection in computerized tomography (CT)-based broncho-alveolar lavage (BAL) fluid and serum for the diagnosis of invasive pulmonary aspergillosis (IPA) in haemato-oncological patients with neutropenia. CT of the thorax and BAL were performed systematically at predefined clinical indications. GM was determined by sandwich enzyme-linked immunosorbent assay; the clinicians were unaware of the results. Of 160 patients, 17 patients (10.6%) presented with proven, probable or suspected IPA. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of GM detection in CT-based BAL fluid were all 100%. For GM detection in serially sampled serum, the sensitivity was 47%, the specificity 93%, the PPV 73% and the NPV 82%. A non-blinded follow-up study was performed to validate these results. In this study, 22 of 198 patients (11.1%) presented with IPA, and the sensitivity, specificity, PPV and NPV of GM detection in CT-based BAL fluid were 85%, 100%, 100% and 88% respectively. None of BAL fluids obtained after antifungal treatment of 3 d or more were positive. These results indicate that, when CT is used systematically and at an early stage, GM detection in CT-based BAL fluid has a high PPV for diagnosing IPA early in untreated patients.

Aspergillus infections in allogeneic stem cell transplant recipients: have we made any progress?

Invasive aspergillosis (IA) is common in allogeneic SCT recipients, with an incidence of 4-10%. The majority of these infections are diagnosed several months after SCT and they are frequently associated with GVHD. The diagnosis is difficult and often delayed. Established IA is notoriously difficult to treat with a death rate of 80-90%. This review summarises recent data on this problem to assess whether there has been any progress. Effective prophylactic measures are still lacking. Severe immunosuppression is the main obstacle to the success of therapy. Recent and ongoing developments in diagnostic measures and new antifungal agents may improve treatment results to some extent, but Aspergillus infections still remain a formidable problem in allogeneic transplantation. Further studies in this field will focus on the role of various cytokines and combinations of antifungal agents.

Prophylaxis, empirical therapy, or pre-emptive therapy of fungal infections in immunocompromised patients: which is better for whom?

Immunocompromised patients are at risk of developing fungal infections. Over time, the incidence of fungal infections and the spectrum of causative organisms have changed. In addition, treatment strategies in this high-risk population have also changed. Traditional approaches (using polyene-based therapy and older azoles), including empirical treatment strategies, have evolved to include prophylaxis in populations at the greatest risk. These strategies, although effective against Candida species, have not really impacted infections caused by Aspergillus spp. With the recent approval of antifungal agents with demonstrated activity against Aspergillus and other mould infections, there is hope for better outcomes in the treatment of established infections. Several agents, with activity against Aspergillus, have been shown to be effective in the empirical setting. The role of these new antifungal agents in the prophylactic setting remains unknown at present, but the potential for reducing Aspergillus infections is promising and requires ongoing study. The other area of significant research in fungal infections has been the search for accurate, non-invasive, rapid diagnostic tests. Over the past year, several publications have indicated that early diagnosis is possible in immunocompromised patients. These new diagnostics have paved the way for a new strategy, called pre-emptive therapy, enabling infected patients to be identified at an earlier stage of infection. This strategy will permit targeted antifungal therapy in those at greatest risk, and will avoid unnecessary, potentially toxic therapy in those not infected. Validations of the various techniques show promise and are reviewed in this paper.

Invasive pulmonary aspergillosis

Invasive pulmonary aspergillosis is the most common fungal pulmonary infection in certain immunocompromised patients. The most commonly affected patients are hematopoietic stem cell transplant recipients and patients with hematological malignancies undergoing intensive chemotherapy. The survival of patients with invasive pulmonary aspergillosis is very poor because of difficulties in early diagnosis and lack of effective treatment options. Research efforts are being made constantly to improve different diagnostic techniques. Early, repeated, high resolution computed tomography of the chest, and sequential nonculture-based monitoring of Aspergillus antigen and DNA can improve earlier diagnosis. New antifungal drugs for treatment and prevention of invasive pulmonary aspergillosis continue to emerge, with better safety, efficacy, and pharmacologic profiles.

Invasive aspergillosis in allogeneic stem cell transplant recipients: increasing antigenemia is associated with progressive disease

The kinetics of serum Aspergillus galactomannan, as determined by enzyme-linked immunosorbent assay, was examined in 37 allogeneic stem cell transplant (SCT) recipients treated for invasive aspergillosis (IA). Fifty-eight periods of response ("response episodes") were evaluated. There were 42 response episodes that were considered "treatment failures" and 16 that were considered "good" (that is, complete or partial) responses. At baseline (the first day of each new response episode), the patients who experienced treatment failure and those who had good responses did not differ significantly with regard to median galactomannan index (GMI) value. Thereafter, GMI values significantly increased in the treatment failure group, whereas no significant changes were observed in the good response group (P=.002). An increase in the GMI value of 1.0 over the baseline value during the first week of observation was predictive of treatment failure with a sensitivity of 44%, a specificity of 87%, and a positive predictive value of 94%. We conclude that serial determination of serum GMI values is a useful tool for assessing prognosis of IA in allogeneic SCT recipients during treatment.

Aspergillus galactomannan detection in the diagnosis of invasive aspergillosis in cancer patients

PURPOSE

To assess the Aspergillus galactomannan enzyme-linked immunosorbent assay (ELISA) in the diagnosis of invasive aspergillosis (IA) in adult and pediatric oncohematologic patients.

PATIENTS AND METHODS

The study was conducted in four patient groups: those with fever of unknown origin (FUO) during neutropenia, suspected pulmonary infection (PI), or nonpulmonary aspergillosis (NPA) and those undergoing surveillance (S) after hematopoietic stem-cell transplantation (HSCT). IA was classified as definite, probable, or possible, according to European Organization for Research and Treatment of Cancer/Mycosis Study Group definitions.

RESULTS

A total of 3,294 serum samples were collected during 797 episodes (FUO, 261; PI, 297; NPA, 28; and surveillance, 211), and 153 episodes of IA were diagnosed (31 definite, 67 probable, and 55 possible). Three episodes were first suspected from galactomannan ELISA; the remaining 150 cases were diagnosed from clinical or radiologic evidence. Sensitivity of the ELISA was 64.5%, 16.4%, and 25.5% in definite, probable, and possible episodes of IA, respectively, and was lower in patients positive for anti-Aspergillus antibodies than in antibody-negative patients. Most false-positive results occurred in children and in allogeneic HSCT (allo-HSCT) patients. Overall specificity of the ELISA was 94.8%. It was lower in children compared with adults (P <.0001) and in allo-HSCT patients compared with non-allo-HSCT adults (P =.0002). Lowering the ELISA cutoff value from 1.500 to 0.700 seemed more relevant for non-allo-HSCT adults (sensitivity, 73.1%, 44.3%, and 44.7% in definite, probable, and possible IA, respectively; specificity, 94%).

CONCLUSION

Galactomannan ELISA seems less sensitive than previously described, and sensitivity can be further reduced by the presence of anti-Aspergillus antibodies. A new cutoff value for the ELISA of 0.700 is proposed for non-allo-HSCT adults.

Recent progress in the diagnosis of fungal infections in the immunocompromised host

The management of invasive fungal infections has been hampered by the inability to diagnose the infection at an early stage of disease. Although proving the presence of infection by histology and culture remains the cornerstone of the diagnosis, non-culture based methods are becoming available that enable early detection. Molecular diagnosis by PCR appears very promising since fungal DNA can be detected in the blood of infected patients before conventional methods. Furthermore, a broad range of yeasts and molds can be identified to species level. Automation of sample preparation and use of real-time PCR systems will help standardize the procedure and reduce false positive results due to contamination. Promising assays for the detection of fungal antigens in serum have been commercialized, including detection systems for mannan (Candida) and galactomannan (Aspergillus). Circulating antigens can be detected at an early stage of infection, often before the onset of clinical symptoms. Antigen detection is limited to detecting only one genus and not enabling speciation. Furthermore, both PCR and antigen detection can be used to monitor the response of patients to treatment with anti-fungal agents. Although prospective screening of high-risk patients for the presence of circulating markers of fungal infection appears to be an appropriate strategy, studies are needed to help to establish the optimal approach to managing invasive fungal infections that incorporates the benefits of non-culture based methods.