Serodiagnosis of invasive aspergillosis in patients with hematologic malignancy: validation of the Aspergillus fumigatus antigen radioimmunoassay

Invasive Aspergillosis in Neutropenic Patients with Hematological Disorders

Between 1983-1988, 72 patients with acute leukemia and 4 with aplastic anemia were treated in the Hematology Unit of The Chaim Sheba Medical Center. Ten patients with acute leukemia developed invasive pulmonary aspergillosis and 2 with aplastic anemia developed invasive aspergillosis of the nose and paranasal sinuses. These infections were diagnosed during a period of profound neutropenia while these patients were receiving broad spectrum antibiotics. The diagnosis of pulmonary aspergillosis was based on positive sputum cultures in 4 cases and on the appearance of typical clinical and radiologic features in six. In 2 culture-positive and in one culture-negative patient, the diagnosis was confirmed at autopsy. Thus, the diagnosis was definitive in 5 patients and probable in the remaining five patients. The 5 patients who achieved remission responded to antifungal treatment and recovered, while of the 5 who eventually died from the fungal infection, 4 did not achieve remission, and one died while in complete remission. In the 2 patients with aplastic anemia, aspergillosis was detected in cultures from necrotic nasal tissue. Both patients remained neutropenic, failed to respond to antifungal treatment and died within a short time after diagnosis. From this experience it appears that invasive aspergillosis in neutropenic patients is potentially curable if treated early by amphotericin B, provided that the neutrophil count recovers.

Galactomannan antigen detection in the diagnosis of invasive aspergillosis

Invasive aspergillosis is a serious and lethal infection among immunocompromised patients, with reported mortality rates as high as 74-92%. The high mortality is related to the severe immunosuppression experienced by these patients as well as the difficulties for physicians in arriving at a timely diagnosis. Definitive diagnostic procedures (tissue biopsy for histopathology and culture) are often precluded by severe cytopenias and coagulation abnormalities. The development of minimally invasive, nonculture diagnostic methods is a major advance in the early diagnosis of invasive aspergillosis. Galactomannan is a heteropolysaccharide (mannan core and side residues of galactofuranosyl units) present in the cell wall of Aspergillus spp. The double sandwich enzyme immunoassay, which detects galactomannan in serum samples, has been available in Europe for almost a decade and in the USA since May 2003, for the diagnosis of invasive aspergillosis. However, availability of the double galactomannan enzyme immunoassay is center variable in the USA and, although its analytical performance in the diagnosis of invasive aspergillosis is well documented, its routine use in clinical practice is limited. As an adjunct in the diagnosis and management of invasive aspergillosis, incorporation of the galactomannan enzyme immunoassay into clinical trials will help to further define its role.

Risk stratification for invasive aspergillosis: early assessment of host susceptibility

Outcomes of invasive aspergillosis are substantially improved with early initiation of therapy. Unfortunately, the diagnosis remains difficult to establish so that early suspicion of infection is imperative. Identification of high risk patients and use of non-culture-based diagnostics and radiographic studies can facilitate earlier recognition of infection. It is important to realize that the timing and spectrum of risk for invasive aspergillosis have expanded. While patients with hematological malignancies and hematopoietic stem cell transplants make up the highest risk groups, patients such as those receiving steroids and other immunosuppressive therapies are also at risk. Non-culture-based methods (including galactomannan, 1,3-beta-D-glucan, and PCR-based methods) are actively being pursued to improve early diagnosis. Thus, identifying patients at high risk for infection and utilizing non-culture-based methods and radiologic studies to assist in establishing a likely diagnosis of invasive aspergillosis will further enhance the role of new agents in the early, effective treatment and prophylaxis of invasive aspergillosis.

Advances in the serological diagnosis of invasive Aspergillus infections in patients with haematological disorders

A reliable diagnosis of invasive aspergillosis in patients with haematological malignancies is seldom achieved antemortem. Conventional laboratory diagnostic methods are insensitive and time-consuming, resulting in late diagnosis and treatment and contributing to unacceptably high mortality. As a result, routine antifungal prophylaxis and early empirical treatment have been recommended. However, overtreatment associated with these strategies results in increased toxicity and cost. The use of sensitive and rapid non-culture-based diagnostic assays, such as detection of Aspergillus antigens (galactomannan, beta-D-glucan) or detection of genomic DNA sequences may allow a shift in emphasis from empirical to pre-emptive therapy, especially when substantiated by suggestive radiological findings. These new tools may be used to confirm a presumed diagnosis of invasive aspergillosis, or, when used to screen high-risk patients, may identify an infection at the early stage of disease. The excellent negative predictive value of these assays should convince clinicians to withhold antifungal therapy in persistently febrile neutropenic patients with no other signs of fungal infection. On the other hand, consecutive positive results in a high-risk population should at least trigger a complete diagnostic work-up. This review will focus on the diagnostic utility as well as on the pitfalls of serial screening for the presence of circulating fungal antigens in haematology patients.

Micromechanical cantilever array sensors for selective fungal immobilization and fast growth detection

We demonstrate the use of micromechanical cantilever arrays for selective immobilization and fast quantitative detection of vital fungal spores. Micro-fabricated uncoated as well as gold-coated silicon cantilevers were functionalized with concanavalin A, fibronectin or immunoglobulin G. In our experiments two major morphological fungal forms were used--the mycelial form Aspergillus niger and the unicellular yeast form Saccharomyces cerevisiae, as models to explore a new method for growth detection of eukaryotic organisms using cantilever arrays. We exploited the specific biomolecular interactions of surface grafted proteins with the molecular structures on the fungal cell surface. It was found that these proteins have different affinities and efficiencies to bind the spores. Maximum spore immobilization, germination and mycelium growth was observed on the immunoglobulin G functionalized cantilever surfaces. We show that spore immobilization and germination of the mycelial fungus A. niger and yeast S. cerevisiae led to shifts in resonance frequency within a few hours as measured by dynamically operated cantilever arrays, whereas conventional techniques would require several days. The biosensor could detect the target fungi in a range of 10(3) - 10(6) CFUml(-1). The measured shift is proportional to the mass of single fungal spores and can be used to evaluate spore contamination levels. Applications lie in the field of medical and agricultural diagnostics, food- and water-quality monitoring.

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.

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

Microbiological diagnosis of invasive fungal infections in transplant recipients

Invasive fungal infections remain an important cause of morbidity and mortality in transplant recipients. Since conventional diagnostic tools such as culture lack sensitivity and specificity, alternative diagnostic assays have been developed. Among the most promising techniques are the detection of fungal DNA and serology. Fungal DNA can be detected with high sensitivity and specificity when performed with specimens from sterile sites such as blood. Polymerase chain reaction (PCR) assays can be used to detect a broad range of fungal pathogens and combined with species identification. Multicenter diagnostic studies are needed to establish the diagnostic value of PCR but lack of standardization hampers such studies. The serodiagnosis of invasive fungal infections has become an important tool in the management of invasive fungal infections. Especially the detection of circulating galactomannan has been shown to be a sensitive marker for invasive aspergillosis. Both serology and PCR can be used to monitor the response to antifungal therapy. The optimal use of non-culture-based methods is in prospective screening of patients at high risk. Since the incidence of disease greatly influences the positive predictive value, screening should take place only in those patients at very high risk for invasive fungal disease.

Aspergillus antigen testing in bone marrow transplant recipients

AIMS

To assess the clinical usefulness of a commercial aspergillus antigen enzyme linked immunosorbent assay (ELISA) in the diagnosis of invasive aspergillosis (IA) in bone marrow transplant recipients, and to compare it with a commercial latex agglutination (LA) test.

METHODS

In total, 2026 serum samples from 104 bone marrow transplant recipients were tested. These comprised 67 sera from seven patients who had died with confirmed IA, 268 sera from nine patients who had died with suspected IA, and 1691 sera from 88 patients with no clinical, radiological, or microbiological signs of IA.

RESULTS

The ELISA was more sensitive than the LA test. All patients who were ELISA positive were also LA positive, and a positive LA result never preceded a positive ELISA. Twelve of 16 patients with confirmed or suspected IA were ELISA positive on two or more occasions, compared with 10 of 15 who were LA positive. ELISA was positive before LA in five patients (range, 2-14 days), and became positive on the same day in the remainder. Aspergillus antigen was detected by ELISA a median of 15 days before death (range, 4-233). Clinical and/or radiological evidence of IA was noted in all patients, and a positive ELISA was never the sole criterion for introduction of antifungal treatment. Two samples (one from each of two patients without IA) gave false positive results.

CONCLUSIONS

The aspergillus ELISA is a specific indicator of invasive aspergillosis if the criterion of two positive samples is required to confirm the diagnosis. However, the test is insufficiently sensitive to diagnose aspergillosis before other symptoms or signs are apparent, and hence is unlikely to lead to earlier initiation of antifungal treatment. It is therefore unsuitable for screening of asymptomatic patients at risk of invasive aspergillosis, but does have a useful role in confirming the diagnosis in symptomatic patients.

Aspergillus Fumigatus antigen detection in sera from patients at risk for invasive aspergillosis

We have developed an inhibition enzyme immunoassay (inhibition-EIA) to monitor for the occurrence of invasive aspergillosis (IA) in sera from 45 immunocompromised (IC) patients. The test uses rabbit polyclonal antibodies and a mixture of components from Aspergillus fumigatus, containing three predominant antigens with molecular weights of 18,000, 33,000, and 56,000. Circulating antigens were found in five of seven proven cases of IA due to A. fumigatus. In two of the five positive cases, antigenemia was detected with inhibition-EIA earlier than with X ray or other biological methods. No antigens were detected in the sera from two patients with proven IA due to Aspergillus flavus and Aspergillus terreus nor in the sera from four patients with probable IA. Circulating antigens were not detected in the control group, composed of 30 healthy adult blood donors. Four of the 32 at-risk patients examined, though they displayed no definite evidence of IA, gave a positive result in this test. The sensitivity, specificity, and positive predictive value of inhibition-EIA were 71.4, 94.4, and 71.2%, respectively. The data were compared with those obtained by a latex agglutination assay of galactomannan (GM) that was positive in only one patient with probable IA. The higher sensitivity obtained by inhibition-EIA may well be due to its ability to detect circulating antigens other than GM in the sera of IC patients with IA. Detecting these antigens may improve the diagnosis of IA, as they may serve as markers of this infection.

Autopsy-controlled prospective evaluation of serial screening for circulating galactomannan by a sandwich enzyme-linked immunosorbent assay for hematological patients at risk for invasive Aspergillosis

Efforts to improve the diagnosis of invasive aspergillosis (IA) have been directed towards the detection of fungal antigens, including galactomannan (GM). However, previous evaluations of GM detection have been hampered by a lack of proven cases of IA and by a nonserial study design. This prospective study assessed the diagnostic value of serial screening for circulating GM by using a recently developed sandwich enzyme-linked immunosorbent assay (ELISA) for prolonged-neutropenic and/or steroid-treated patients with hematological disorders. Serum GM levels were monitored twice weekly for 186 consecutive patients at increased risk for IA. The patients were stratified according to the likelihood of IA (proven, probable, possible, and no evidence of IA) by using stringent criteria. Proven IA was defined by characteristic histopathological findings together with a positive culture for Aspergillus species. Autopsy and culture from autopsy specimens was used to verify both positive and negative test results. A total of 2,172 serum samples were tested from 243 episodes (mean, 9 samples/episode). Based on the analysis of 71 patients with confirmed disease status (culture and histology), the sensitivity and specificity of serial GM monitoring were 92.6 and 95.4%, respectively. The positive predictive value was almost 93%, the negative predictive value was 95%, and the efficacy was 94%. False-positive reactions occurred at a rate of nearly 8%, although this figure might have been overestimated. Less than 1% of all tested sera were considered inconclusive. In more than half of the cases, antigenemia was detected before clinical suspicion of IA (median, 6 days before). Serial determination of serum GM by the sandwich ELISA technique is a sensitive tool for the diagnosis of IA in hematological patients at risk. This approach may substantially influence clinical management with regard to preemptive and empirical antifungal therapy.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Detection of antigen in sera of patients with invasive aspergillosis: intra- and interlaboratory reproducibility. The Dutch Interuniversity Working Party for Invasive Mycoses

The intra- and interlaboratory reproducibilities of a commercial sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of Aspergillus galactomannan in serum (Platelia Aspergillus; Sanofi Diagnostics Pasteur, Marnes-La-Coquette, France) were evaluated in six laboratories of university hospitals. Twenty serum samples were obtained from 12 neutropenic patients including 6 with invasive aspergillosis. These samples were blinded and sent to each center together with eight blinded ELISA-negative serum samples spiked with known concentrations of galactomannan. The centers were provided with ELISA microtiter plates from a single batch and a detailed protocol. Ten clinical samples showed ELISA reactivity, while 10 samples were ELISA negative. The mean coefficient of variation (CV) of the optical density values was 4.24% within a single assay and 25.6% between runs. The interassay CV of the ratios for the serum samples tested was 18.6%. Analysis of ordinal interpretation of the ELISA result (i.e., negative, gray zone, or positive) showed excellent reproducibility. Recalculation of the cutoff values for positive and negative samples suggested that the cutoff level recommended by the manufacturer could be lowered from 1.0 to 0.8 for negative samples and from 1.5 to 1.0 for positive samples. The intra- and interlaboratory reproducibilities were excellent when the ELISA results were interpreted as ordinal data, but considerable variation in optical density values and, to a lesser extent, in the ratios for the serum samples tested, was observed between runs. High assay variability was also found for serum samples spiked with known concentrations of galactomannan. Therefore, antigen titers in serum samples from a single patient, measured in different runs, should be compared with caution.

Recent progress and current problems in treatment of invasive fungal infections in neutropenic patients

Invasive fungal infections, including disseminated candidiasis and invasive pulmonary aspergillosis, are important causes of morbidity and mortality in neutropenic patients. The recent development of fluconazole, itraconazole, lipid formulations of amphotericin B, and recombinant cytokines have expanded our therapeutic armamentarium. Clinical trials have elucidated new strategies for utilizing these compounds in the prevention and treatment of opportunistic mycoses. The population of more severely immunocompromised patients, however, continues to expand and the spectrum of drug-resistant fungi, including but not limited to Candida spp, Fusarium spp, Zygomycetes, and dematiaceous moulds, continues to evolve, thus presenting new challenges to recent therapeutic advances. Development of new antifungal chemotherapeutic agents and novel approaches for augmentation of host response will be required to meet these new mycologic challenges.

Prospective sandwich enzyme-linked immunosorbent assay for serum galactomannan: early predictive value and clinical use in invasive aspergillosis

BACKGROUND

The delay between the onset of invasive aspergillosis and the start of antifungal therapy is crucial for the patient's recovery. Early diagnosis is difficult in cancer patients through lack of precocious specific signs. We have investigated the clinical usefulness of circulating Aspergillus antigen monitoring in pediatric hematology patients with a new sensitive sandwich enzyme-linked immunosorbent assay.

METHODS

A prospective study was conducted by assessing circulating galactomannan levels in high risk patients. Thirty-seven patients studied during an 18-month period were evaluated twice weekly during neutropenic phases with the sandwich enzyme-linked immunosorbent assay for serum Aspergillus galactomannan.

RESULTS

Twelve patients had one or more episodes of positive circulating galactomannan detection, 10 of whom developed presumptive invasive aspergillosis. The clinical and radiologic signs occurred at a mean of 13.4 days (range, 0 to 48) after circulating galactomannan detection and reversed in 6 patients treated with amphotericin B at the same time circulating galactomannan detection became negative. Reappearance of circulating galactomannan was observed during subsequent neutropenic periods in 3 patients.

CONCLUSIONS

The detection of galactomannan at concentrations as low as 1 ng/ml can be useful for the early initiation of antifungal therapy and monitoring treatment in clinically documented lung aspergillosis. This technique coupled with chest computed tomography could help to restrict the need of invasive diagnostic procedures in fragile patients.

Comparison of an enzyme immunoassay and latex agglutination test for detection of galactomannan in the diagnosis of invasive aspergillosis

Aspergillus antigenemia was followed up in 215 consecutively observed bone marrow transplant (BMT) patients over a period of two years, using both a latex agglutination test and a sandwich immunocapture enzyme immunoassay (EIA) with a rat antigalactomannan monoclonal antibody as capture and detector antibody. For each patient, sequential sera (3 to 20) were obtained before and after BMT. No positivity was observed before BMT. After BMT, the EIA and latex agglutination test were positive in 19 and 4 patients respectively of 25 patients with confirmed aspergillosis and 14 and 7 of 15 patients with probable aspergillosis. In 19 of 25 patients with confirmed aspergillosis and 9 of 15 patients with probable aspergillosis, the EIA was more sensitive and detected infection earlier than the latex test. In all positive cases, antigenemia rapidly increased in sequential samples and remained strongly positive. In 31 of 169 (19%) BMT patients without clinical signs of aspergillosis, the EIA was occasionally positive in samples taken within the first month after BMT, giving a specificity of 81% in these patients. In non-BMT patients suffering from other diseases (n = 77), the specificity was 98.7%. The overall positive and negative predictive values for the EIA were 54% and 95% respectively. These results favour the use of EIA for early diagnosis and monitoring of aspergillosis in BMT patients, although the predictive value of transient positivity remains to be ascertained.

Clinical evaluation and reproducibility of the Pastorex Aspergillus antigen latex agglutination test for diagnosing invasive aspergillosis

AIMS

The performance of the Pastorex Aspergillus antigen latex agglutination test for the detection of galactomannan in sera of patients at risk for invasive aspergillosis was evaluated, and the impact of storage on the reproducibility of the antigen titre was tested.

METHODS

During a one year period, 392 serum samples were obtained from 46 patients at risk for invasive aspergillosis and tested for the presence of galactomannan using an Aspergillus latex agglutination test (Pastorex). Twenty three positive serum samples which had been stored at -20 degrees C for 2-16 months were retrospectively retested. Furthermore, two positive serum samples were stored at -20 degrees C and -70 degrees C and prospectively tested at three month intervals for a period of 15 months.

RESULTS

The Pastorex Aspergillus test was positive in eight patients with microbiological, radiological, or histological evidence for invasive aspergillosis, but was negative in the initial serum sample from five of these patients. In two patients with histological evidence for invasive aspergillosis no positive reaction was found in six samples. Six of 13 (45%) serum samples which had been stored at -20 degrees C for longer than six months had lost reactivity, while one of 10 (10%) samples had lost reactivity when stored up to six months. Two serum samples which had been stored at -20 degrees C and -70 degrees C and prospectively retested at three month intervals for 15 months, maintained stable antigen titres.

CONCLUSIONS

The Pastorex Aspergillus test is too insensitive to diagnose invasive aspergillosis in an early stage, but may contribute to the diagnosis when cultures remain negative and serial samples are obtained. To maintain a good reproducibility, serum samples should be stored at -70 degrees C when the period of storage exceeds six months.

A new sensitive sandwich enzyme-linked immunosorbent assay to detect galactofuran in patients with invasive aspergillosis

A double-direct sandwich enzyme-linked immunosorbent assay that uses a rat anti-galactomannan monoclonal antibody as the acceptor and detector antibody was designed. This immunoassay, which detects less than 1 ng of galactomannan per ml, was assessed in a retrospective study with samples from patients with invasive aspergillosis. Serum is more appropriate than urine for use in the search for circulating galactomannan. Antigenemia does not have a transient character. Galactomannan can be detected at least 39 days before the death of the patients.

Detection of (1-3)-beta-D-glucan in a rat model of aspergillosis

The G test containing factor G, fractioned from the Limulus lysate, was used to detect (1-3)-beta-D-glucan in a rat model of aspergillosis. Aspergillus fumigatus strain MF-13, 1 x 10(4) conidia, were inoculated transtracheally into rats treated with cortisone acetate (100 mg/kg) and fed a low-protein (8%) diet. Increased serum (1-3)-beta-D-glucan was found on the sixth day after inoculation in concentrations of 370 +/- 178 pg/ml (mean +/- SD) in untreated controls, and 154 +/- 43 pg/ml in rats treated with 0.5 mg/kg of amphotericin B. On day 11 (1-3)-beta-D-glucan concentrations were 2,590 +/- 2,940 pg/ml and 448 +/- 442 pg/ml, respectively. The elevation in levels of (1-3)-beta-D-glucan increased in correlation with the elevation of galactomannan antigen titers; (1-3)-beta-D-glucan is thus measurable during experimental aspergillosis in rats.

Value of antigen and antibody detection in the serological diagnosis of invasive aspergillosis in patients with hematological malignancies

In a study to determine the value of antigen and antibody detection in the serological diagnosis of invasive aspergillosis in patients with hematological malignancies, 436 sequential serum samples from 79 neutropenic patients were tested. Circulating galactomannan antigen was detected with a latex agglutination method (Pastorex Aspergillus) and antibody to Aspergillus fumigatus with an immunodiffusion test on agar gel. Among the 79 patients 18 cases of invasive aspergillosis were detected (4 proven, 6 highly probable, 3 probable, 5 suspected). Antigen was detected in 7 of these 18 patients. The sensitivity of the antigen test was 38.8% and the specificity 95%. The antibody test showed 55.5% sensitivity and 100% specificity. In this study the antigen test was less sensitive than previously reported but highly specific and might serve as a supplementary diagnostic test.

Experimental systemic bovine zygomycosis with reference to pathology and secretion of antigen into urine

ELISA and immunoblotting were applied for the characterization of somatic antigens from Absidia corymbifera. Immunoblotting revealed major antigenic bands at 11 to 81 kDa. The ELISA showed some crossreactivity towards somatic antigens from other fungi. However, the crossreactivity was especially observed with somatic antigens from other fungi of the zygomycetes. The ELISA and immunoblotting assays were applied to urine samples from two groups of 3 calves each systemically infected with A. corymbifera and Aspergillus fumigatus, respectively. The immunoreactivity of the urine samples was similar by the two assays. Somatic antigens were demonstrated in the urine of all three calves infected with A.corymbifera, whereas only one of the calves with systemic aspergillosis was antigen positive. The level of antigen in the positive urine samples varied from 50 to 210 ng/ml.

What's new in fungal infection in leukemic patients

Fungal infections have become an important cause of mortality in patients with hematological malignancies. In recent years, fungi such as Candida tropicalis, Aspergillus spp, Fusarium spp and Trichosporon spp have emerged as important pathogens. Amphotericin B remains the antifungal agent with the broadest spectrum of activity, although some of the newer pathogens may be resistant. The administration of this drug in lipid vehicles reduces the toxicities, permitting the administration of higher doses that may be more effective. The new agents, fluconazole and itraconazole, have activity against some fungal pathogens, although their role in therapy has not been fully determined. Fluconazole has been shown to be effective for prophylaxis of Candida infections.

The value of bronchoalveolar lavage and bronchial washings in the diagnosis of invasive pulmonary aspergillosis

The objective of this study was to clarify conflicting reports of the sensitivity and specificity of bronchoalveolar lavage or bronchial washings for diagnosing invasive pulmonary aspergillosis. The study was a retrospective review of 300 consecutive patients in a tertiary referral centre subjected to 343 fiberoptic bronchoscopic procedures for the evaluation of pulmonary infiltrates. Classification of paired fungal culture and cytologic examination of bronchoalveolar lavage or bronchial washing fluid according to clinical, radiographic, histological and autopsy evidence of invasive pulmonary aspergillosis. One-hundred and fifteen deaths occurred, with a 58% autopsy rate. A diagnosis of invasive pulmonary aspergillosis was made in 21 immunosuppressed patients with 16 deaths. Bronchoalveolar lavage cytology showed aspergillus in 19 specimens (invasive pulmonary aspergillosis in 16), cultures yielded aspergillus in 41 (invasive pulmonary aspergillosis in ten), with both tests positive in nine. Cytology sensitivity was 64.0%, specificity 99.1%, positive predictive value 84.2%, and negative predictive value 97.2%. Culture sensitivity was 40.0%, specificity 90.3%, positive predictive value 24.4%, and negative predictive value 95.0%. Concordant cytology and culture sensitivity was 32.0%, specificity 99.7%, positive predictive value 88.9%, and negative predictive value 94.9%. In conclusion, when characteristic hyphae are visualized in bronchoalveolar lavage specimens from immunosuppressed patients with compatible clinical data, it is advisable to treat for presumptive invasive pulmonary aspergillosis.

Antigenemia in paracoccidioidomycosis

Severe forms of paracoccidioidomycosis (Pcm) are accompanied by intense immunological involvement characterized by depression of the cell-mediated immune response and by high levels of antibodies in serum with no protective function. These changes can be reversed by antifungal treatment. It has been suggested that antigens of Paracoccidioides brasiliensis released into the circulation during the active phase of the disease may be involved in the genesis of the changes in the immune response. In the present study, we evaluated the antigenemia of patients with Pcm using a competitive enzyme-linked immunosorbent assay (ELISA-c) capable of detecting 6 ng of antigen per ml of serum. Twenty-seven of 88 serum samples tested gave positive results, with the highest frequency of positivity being detected in patients with the severe acute form of the disease; these patients had the highest antigen levels (0.03 to 3.4 micrograms/ml). Follow-up of one case showed a correlation between antigen levels in serum and evolution of the disease. False-positive reactions were observed in sera from patients with histoplasmosis, aspergillosis, and cryptococcosis. The results indicate that the described method has potential for clinical application, especially with respect to the evaluation of disease activity. Quantification of fungal antigens in the serum of patients with active Pcm represents an objective parameter for the study of the physiopathology of the disease.

Low-dose amphotericin B prophylaxis against invasive Aspergillus infections in allogeneic marrow transplantation

PURPOSE

Invasive Aspergillus infections cause significant morbidity and mortality in marrow transplant patients. In this study, we examined whether administration of intravenous low-dose prophylactic amphotericin B could reduce the incidence and mortality associate with invasive aspergillosis in patients undergoing allogenic marrow transplantation.

PATIENTS AND METHODS

The subjects of this analysis were 186 consecutive patients undergoing allogeneic marrow transplantation in an adult bone marrow transplant unit between July 1, 1985, and September 30, 1990, utilizing consistent disease-specific chemoirradiation and graft-versus-host disease protocols. The incidence, morbidity, and case fatality of invasive aspergillosis in the study group receiving amphotericin chemoprophylaxis were compared with that in two historic cohorts managed without prophylactic amphotericin B. Univariate and multivariate statistical analyses were performed to examine whether an apparent protective effect could be attributed to differences in patient and treatment variables among the cohorts and to determine potential toxicities of the chemoprophylaxis regimen.

RESULTS

There was a significant reduction in both the incidence (p = 0.003) and mortality (p = 0.03) of invasive aspergillosis in patients receiving amphotericin B chemoprophylaxis as compared with those not receiving chemoprophylaxis. The prophylactic amphotericin B schedule, as employed here, was not associated with increased renal or hepatic toxicity as compared with that in historically managed patients.

CONCLUSION

These data suggest that the risks of invasive aspergillosis in allogeneic marrow transplant recipients can be reduced by administration of prophylactic amphotericin B during the pretransplant and peritransplant periods.

Antigen detection in invasive aspergillosis

The application of a reverse passive latex agglutination test and dot-blot assay are reported in the diagnosis of 50 proven cases of invasive aspergillosis and 28 suspected cases. At a latex titre cut off of greater than or equal to 1 in 8 the test had a sensitivity of 29.4%, specificity of 96.3% and efficiency of 41.4%. This was in sera taken when the diagnosis was first suggested. The sensitivity rose to 55.1% when sera with the maximum level of antigen were examined. The dot blot was more sensitive with 33.3% of cases being positive in the initial sera. This increased to 61.5% when the serum with the maximum antigen level was taken.

Immunodiagnosis of aspergillosis

Aspergillus species are ubiquitous fungi and have been implicated as the causative agents of a variety of lung disorders in humans. These disorders include allergic, saprophytic, and systemic manifestations. The allergic disorders mainly affect atopic persons, and invasive or systemic diseases affect immunosuppressed individuals. Immunodiagnosis can help the practitioner diagnose these diseases. Demonstration of circulating antibodies is a useful criterion, but the lack of dependable and standardized antigens is a limiting factor in the diagnosis of most Aspergillus-induced diseases. Despite this limitation, however, immunodiffusion and enzyme-linked immunosorbent assays have been widely used for the detection of antibodies in the sera of patients with aspergillosis. Similarly, crude and semipurified antigens are being used to demonstrate skin hypersensitivity in patients, and several methods have been useful in the detection of antigenemia in patients with invasive aspergillosis. With a growing number of reports on the incidence of aspergillosis and an increase in the number of immunosuppressed individuals in the population, more rapid methods and more reliable reagents for immunodiagnosis are needed. With recent attempts at obtaining reliable reagents for through hybridoma technology and molecular biological techniques, substantial progress toward efficient immunodiagnosis may be achieved.

Model of recurrent pulmonary aspergillosis in rats

Male Sprague-Dawley rats were treated with cortisone acetate and fed a low-protein diet for 3 weeks. At the end of week 2, animals were infected intratracheally with 10(5) conidia of Aspergillus fumigatus H11-20. Despite discontinuation of steroids and the low-protein diet 1 week after the infection, 94% of controls died of invasive pulmonary aspergillosis within 3 weeks postinfection. When rats were treated with a single dose of 1.6 mg of aerosolized amphotericin B per kg of body weight 48 h prior to the infection, mortality was reduced to 11% within 3 weeks postinfection. Despite apparent good health and rapid weight gain, all survivors showed multiple lesions in histopathological sections of the lungs, and 10(3) to 10(4) CFU of aspergilli was recovered from cultures of their lungs. With discontinuation of immunosuppression, the infection was slowly cleared; however, when cortisone acetate was restarted during week 5, reactivation of progressive invasive pulmonary aspergillosis was observed. On the basis of these results, we conclude that a single low dose of aerosolized amphotericin B prophylaxis is effective in preventing an exogenous aspergillus infection of the lung. Additional therapy is needed to prevent recurrent infection caused by endogenous aspergilli when immunosuppression is resumed.

Identification and characterization of an immunodominant 58-kilodalton antigen of Aspergillus fumigatus recognized by sera of patients with invasive aspergillosis

Sera from 38 patients with invasive aspergillosis were tested by Western immunoblotting for the presence of antibodies to antigens of Aspergillus fumigatus present in a mycelial extract of the organism. All of the sera contained antibodies to an antigen of molecular weight 58,000, which was which was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was the only antigen recognized in approximately 90% of the sera tested. The 58-kDa antigen is an abundant component of mycelial extracts composing approximately 50% of the Coomassie blue-stained protein. The antigen also contains carbohydrate, since it is stained by the carbohydrate stain periodic acid-Schiff and it binds to the lectin concanavalin A. It was purified by immunoaffinity chromatography employing a monoclonal antibody directed against an epitope on the 58-kDa antigen. Analysis of the purified antigen by gas-liquid chromatography revealed the presence of mannose, galactose, and glucose residues in a 2:1:2 ratio. The ratio of protein to carbohydrate is 1.16:1. The protein is slightly acidic, containing relatively high quantities of glutamic and aspartic acids, glycine, alanine, serine, and threonine. The 58-kDa antigen also contains phosphate groups as part of its structure. Serological activity was totally destroyed after treatment with sodium metaperiodate and was partially destroyed after treatment with pronase. The 58-kDa antigen was not able to hydrolyze protein.

Value of antigen detection in predicting invasive pulmonary aspergillosis

Two ELISAs were used to detect serum and urinary aspergillus antigen in 121 patients who were profoundly neutropenic after leukaemia therapy or bone marrow transplantation. The presence of antigen correctly predicted development of invasive pulmonary aspergillosis (IPA) in 16 patients. In 2 other cases antigen appeared after the clinical diagnosis had been made, while in only 1 case was antigen not detected. In 11 of 13 episodes of clinically suspected fungal infection antigen was detected before clinical diagnosis was made. By contrast, antigen was detected in only 1 of 90 patients who had no evidence of IPA. Both ELISAs gave positive and negative predictive values for IPA of greater than 95%, demonstrating the value of antigen detection in early diagnosis of aspergillus infection and the assay's ability to predict subsequent development of IPA. We conclude that neutropenic patients should be screened for aspergillus antigen, and propose that initial detection of fungal antigen justifies commencement of empirical antifungal therapy. Such an approach should improve the survival of patients who are at risk of developing this usually fatal infection.

Detection of Aspergillus antigens associated with invasive infection

Serial urine samples were collected from 33 neutropenic patients, 10 of whom developed invasive aspergillosis (IA) while undergoing bone marrow transplantation or remission induction therapy for leukemia. Concentrated urine samples from the infected patients were subjected to polyacrylamide gel electrophoresis, blotted, and then incubated with antiserum raised to a cell wall extract of Aspergillus fumigatus (anti-CW) or an immunoglobulin G monoclonal antibody to A. fumigatus galactomannan (EBA1). When IA patient urine blots were probed with anti-CW, major bands at 11 and 18 kilodaltons (kDa); intermediate bands at 13, 14, and 29 kDa; and minor bands at 38 and 44 kDa were seen. In contrast, EBA1 showed diffuse staining at molecular masses larger than 45 kDa and a single weak band at 21 kDa. Urine samples from the 23 patients with no evidence of IA were unreactive with both anti-CW and EBA1. These antigen bands are likely to represent immunodominant antigens which are excreted during IA and should play a valuable role in the development of rapid diagnostic tests for aspergillosis.

Use of immunoblotting to detect Aspergillus fumigatus antigen in sera and urines of rats with experimental invasive aspergillosis

Immunoblotting was used to detect Aspergillus fumigatus antigen in sera and urines of immunosuppressed rats experimentally infected with A. fumigatus. Organisms were administered by both intravenous and intratracheal injections. Intravenously infected rats developed disseminated aspergillosis, but intratracheally infected rats developed pulmonary disease only. Fungal cultures of blood and urine samples from infected rats were negative. In the urines of intravenously infected rats, antigen was detected 24 to 48 h after infection; in the urines of intratracheally infected animals, antigen was detected on days 4 to 5 after infection. Antigen in serum was detected later than antigen in urine was. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of serum and urine samples, the most strongly reacting antigenic materials were found in the 88-, 40-, 27-, and 20-kilodalton regions. These dominant antigens appeared to be the same as those of control antigens prepared from A. fumigatus grown in vitro. Rabbit antiserum to Aspergillus filtrate antigen was found to be more immunoreactive than antiserum to mycelial or conidial antigen. No mycelium-specific antigens were detected.

Production and characterization of monoclonal antibodies to cell wall antigens of Aspergillus fumigatus

Two murine monoclonal antibodies (MAbs) against Aspergillus fumigatus were produced and characterized. Splenocytes from cell wall-immunized BALB/c mice were fused with SP2/0 myeloma cells. The hybridomas were screened with a cold alkali (CA) extract of mycelium containing protein, mannose, and galactose, and two MAbs of the immunoglobulin M class were purified from ascites fluid. MAbs 1 and 40 were characterized by double immunodiffusion against CA antigen, indirect enzyme immunoassay with mannans of Candida albicans serotypes A or B or Candida tropicalis, indirect immunofluorescence with C. albicans- or A. fumigatus-infected tissues, indirect immunofluorescence with smears of other pathogenic fungi, Western blotting (immunoblotting) with the lectin concanavalin A or BS-1 from the seeds of Bandeirea simplicifolia, and immunoelectron microscopy. MAb 1 did not cross-react with Candida mannan and recognized a periodate-sensitive, pronase- and heat-resistant epitope in CA antigen and three mannose- and galactose-containing components (80, 62, and 49 kilodaltons) of a mycelial homogenate. Immunoelectron microscopy demonstrated binding of MAb 1 to the inner cell wall and intracellular membranes of hyphae and conidia of A. fumigatus. Circulating antigen was detected in experimental invasive aspergillosis by inhibition enzyme immunoassay with MAb 1 and CA antigen. MAb 40 was a nonprecipitating antibody cross-reactive with Candida species, and competition for an epitope located diffusely in the cell wall of A. fumigatus hyphae was demonstrated by incubating MAb 40 with mannan of C. albicans serotype A. These results suggest that MAb 1 recognizes immunodominant oligogalactoside side chains of A. fumigatus galactomannan, while MAb 40 binds to mannopyranosyl side chains common to A. fumigatus galactomannan and C. albicans mannan.

Detection of circulating galactomannan by Pastorex Aspergillus in experimental invasive aspergillosis

The performance of Pastorex Aspergillus, a new latex agglutination test for the detection of circulating galactomannan in the serum of patients with invasive aspergillosis, was evaluated in a blind trial in standardized guinea-pig models of invasive aspergillosis and other invasive mycoses. In these animal models, the invasive nature of the fungal infection was confirmed by re-isolation of the etiologic agent from the organs of every animal. Ninety-two plasma samples from 42 animals with invasive aspergillosis were submitted to the test. In 41 of these animals, at least one plasma sample was positive with the latex test (sensitivity 97.6%), titers ranging from 1/1 to 1/512. In general, antigen titers increased as a function of time, reaching the highest values shortly before death. Guinea-pigs infected with Penicillium marneffei also yielded positive agglutination reactions but antigen titers were lower (maximal titer 1/8). Plasma samples from animals with invasive candidosis (23), disseminated trichophytosis (11) and cryptococcosis (23) were all negative with the latex test. In 80 guinea-pigs without fungal infection, 3 false positive results (titers 1/1) were observed, which means a specificity of 96.2% in this control group.

Fungal infections during neutropenia: the role of prophylaxis

Fungal infections are seen predominantly in patients with neoplastic diseases. Autopsy studies revealed that 30 to 50% of decreased patients with hematologic neoplasms have histopathologically documented invasive fungal infections. The rationale for fungal chemoprophylaxis is the high incidence of fungal disease in these patients (5), the high mortality (29), the difficulty in diagnosing (28), and the severe side effects of systemic antifungal therapy with amphotericin B (3). Endogenous sources such as oropharyngeal and digestive mucous membranes and exogenous pathways such as air (e.g.aspergilli) or food have to be considered. Therefore, prophylaxis has to comprise both aspects:Prevention of acquisition through nonspecific hygiene measures (5), reduction of colonization (non-absorbable antifungals or systemic chemoprophylaxis) (20). Antifungal prophylaxis of candidosis with both non- and absorbable drugs has not been convincing in terms of reduction of proven fungal infections. Prevention of aspergillosis consists mainly of the control of room air.