Aspergillus antigen latex test for diagnosis of invasive aspergillosis

Immunodetection of fungal and oomycete pathogens: established and emerging threats to human health, animal welfare and global food security

Filamentous fungi (moulds), yeast-like fungi, and oomycetes cause life-threatening infections of humans and animals and are a major constraint to global food security, constituting a significant economic burden to both agriculture and medicine. As well as causing localized or systemic infections, certain species are potent producers of allergens and toxins that exacerbate respiratory diseases or cause cancer and organ damage. We review the pathogenic and toxigenic organisms that are etiologic agents of both animal and plant diseases or that have recently emerged as serious pathogens of immunocompromised individuals. The use of hybridoma and phage display technologies and their success in generating monoclonal antibodies for the detection and control of fungal and oomycete pathogens are explored. Monoclonal antibodies hold enormous potential for the development of rapid and specific tests for the diagnosis of human mycoses, however, unlike plant pathology, their use in medical mycology remains to be fully exploited.

[Invasive aspergillosis: results of an 8-year study]

We analysed retrospectively 90 cases of invasive aspergillosis (IA) which occurred at the University Hospital and the Thoraxklinik gGmbH Heidelberg between 1991 and 1998. 71 cases were histologically proven, 19 were probable diseases. There were 49 male and 41 female patients, with a mean age of 51.5 years (range 16 days to 80 years). Underlying diseases were: hematological malignancies in 52% (n = 47; 24 with acute leukemia), solid organ transplantation (n = 11; 9 liver, 1 kidney, 1 heart), solid cancer (n = 10), others (n = 21), and in one case no underlying disease was diagnosed. Only 54 cases (60%) were correctly diagnosed as IA during lifetime of the patients. In 59 cases (65%) only the lung was affected, 25 patients suffered from disseminated IA, in 6 patients only extrapulmonary lesions were present. 11 patients underwent lung surgery, 63 patients received antimycotic drugs (44 amphotericin B, 15 fluconazole, 4 itraconazole), 21 were not treated antimycotically. 68 patients (71%) died, from these 30 (36%) due to IA during remission of the underlying disease. The laboratory methods showed the following sensitivities, respectively: microscopy by calcofluor white staining 17%, culture 69%, Aspergillus-PCR from respiratory tract samples and biopsies 95%, galactomannan antigen detection by latex agglutination 28%, by enzyme immunoassay 59%, Aspergillus antibody detection 23%.

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.

Evaluation of PCR for detection of DNA specific for Aspergillus species in sera of patients with various forms of pulmonary aspergillosis

Pulmonary aspergillosis is classified into invasive, saprophytic, and allergic forms. In this study, we evaluated the usefulness of PCR for differentiating between different forms of aspergillosis or in monitoring disease activity during treatment by detecting DNA specific for Aspergillus species in the serum. Nested PCR was used to detect Aspergillus DNA in the sera of 30 patients with various forms of pulmonary aspergillosis. The results were compared with those of latex agglutination tests for detecting galactomannan antigen. We also examined the serial changes in the results of nested PCR during and after treatment of a subgroup of patients with invasive pulmonary aspergillosis with amphotericin B. The highest proportion of positive nested PCR results were in patients with invasive aspergillosis (10 of 12; 83%), while patients with pulmonary aspergilloma had the lowest frequency of positive tests (1 of 9; 11%). These results suggested that the sensitivity of the nested PCR depends on the extent of invasion by Aspergillus species. Serial assays showed that the results of nested PCR became negative shortly after commencement of antifungal treatment and that such changes did not correlate with clinical responsiveness to treatment. Our results indicate the potential usefulness of nested PCR with serum samples for the diagnosis of invasive aspergillosis and the detection of a shift in the status of infection from a noninvasive type to invasive aspergillosis. However, the results of the nested PCR did not correlate with the response to antifungal treatment.

Lack of utility of the lysis-centrifugation blood culture method for detection of fungemia in immunocompromised cancer patients

We retrospectively compared the utility of a fungal isolation device (Isolator) versus conventional techniques for recovering fungal organisms from blood cultures obtained from neutropenic cancer patients. Positive cultures were deemed true pathogens, possible pathogens, or contaminants according to laboratory and clinical criteria. Fifty-three patients had 66 positive blood cultures for fungi, nine on multiple occasions. In 20 episodes true pathogens were recovered, 6 from broth medium alone, 4 from the Isolator system alone, and 10 from both systems. False-negative cultures were noted in 4 of 20 (20%) cases in which broth medium was used and in 6 of 20 (30%) cases in which the Isolator system was used. Possible pathogens were detected in 4 of 66 blood culture-positive cases. Forty-two positive cultures were considered contaminants, 1 collected from standard medium and 41 of 42 (98%) which grew only in Isolators. Eleven of 18 patients with true fungal infections expired as a result of infection, while 4 of 33 patients with a contaminant expired, none from a fungal cause. We do not advocate the routine use of Isolator tubes in the evaluation of the febrile, neutropenic patient due to the high rates of false positives and of contamination.

Detection of Aspergillus galactomannan antigen in foods and antibiotics

The specificity of the Pastorex Aspergillus latex agglutination test for the diagnosis of manifest aspergillosis is hampered by the occurrence of false-positive results. In order to prove whether or not the false-positive reactions may be caused by the uptake of the soluble galactomannan antigen from the environment, the presence of the antigen was tested in foods, air samples, antibiotics for therapeutic use and faeces. Reactions of the Aspergillus latex agglutination test were found in 15 (79%) out of 19 samples of meals prepared in a hospital kitchen, in five out of six canned vegetables from a supermarket, in all of six samples of pasta and rice bought in health shops, in the faeces of four bone marrow transplant (BMT) recipients and of four healthy subjects and in one and two batches of the antibiotics co-amoxyclav and piperacillin respectively. The concentration of the antigen in faecal material was calculated to be in the range of 1.2-38.4 micrograms g-1. It is concluded that the faecal galactomannan antigen may reach the circulation in patients with dysfunction of the intestinal mucosal barrier, e.g. BMT recipients, thus leading to diagnostically false-positive antigenaemia.

Serum Aspergillus galactomannan antigen testing by sandwich ELISA: practical use in neutropenic patients

The double sandwich ELISA detecting Aspergillus galactomannan (GM) was prospectively evaluated for the diagnosis of invasive aspergillosis (IA) in 50 haematological patients at risk for IA. Serum samples were collected once weekly as long as the risk factors persisted. Six patients had proven or probable IA (3 A. fumigatus, 1 A. flavus, 1 A. niger, 1 A. ustus) and the GM titres were parallel to the clinical evolution of IA. Six of nine patients with suspected IA had at least two consecutive serum GM titres above 1 ng/ml and died with increasing titres, whereas the GM-negative patients survived. Positive GM titres did not anticipate the isolation of fungi. Unfortunately, positive GM titres did not anticipate the initiation of antifungal therapy, based on clinical suspicion. Moreover, if a true-positive result was defined as two consecutive positive serum samples, four patients out of 35 without proven, probable or suspected IA were positive. Then, the rate of false-positive results was high (12%) in the range previously reported. Nevertheless, the GM ELISA appears useful to assess IA and to follow the efficacy of antifungal treatment.

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.

Evaluation of eight antibody tests and one antigen test for the diagnosis of invasive aspergillosis

Eight Aspergillus antibody detection assays--three indirect haemagglutination assays (IHA-LD, IHA-Roche, IHA-Fumouze), three enzyme immunoassays (EIA-IgG, EIA-IgM, EIA-IgA, DDV) and two complement fixation tests (CF-metabolic and CF-somatic, Virion--and one latex agglutination test (LAT) for Aspergillus galactomannan antigen detection (Sanofi Pasteur) were evaluated in 14 patients with proven invasive aspergillosis (a total of 47 serum samples and one cerebrospinal fluid sample) and in 68 selected control individuals (one selected serum sample each). For the antibody tests, sensitivity ranged from 14% to 36% and specificity from 72% to 99%. The antigen detection test had a sensitivity of 36% and a specificity of 100%. Currently commercially available antibody detection assays for the serodiagnosis of invasive aspergillosis are inadequate. The antigen detection test appears to be highly specific, but lacks sufficient sensitivity.

Comparison of antigen detection and PCR assay using bronchoalveolar lavage fluid for diagnosing invasive pulmonary aspergillosis in patients receiving treatment for hematological malignancies

The performance of a sandwich enzyme-linked immunosorbent assay (ELISA) which detects Aspergillus galactomannan (GM) was evaluated in bronchoalveolar lavage (BAL) fluid samples from 19 patients who were treated for hematological malignancies and who were suspected of having invasive pulmonary aspergillosis (IPA). All patients had fever and pulmonary infiltrates on the chest roentgenogram on the day that the BAL fluid was obtained. The ELISA results were compared with the results of culture and Aspergillus genus-specific PCR analysis of BAL fluid samples. ELISA was also performed with serum samples. Aspergillus species were detected by PCR or ELISA with BAL fluid samples from five of seven patients who had radiological evidence of IPA. Serum ELISA results were positive for all patients with ELISA-positive BAL fluid, and for four patients the serum ELISA was positive before the BAL fluid was obtained. PCR and ELISA were positive for 2 and 1 of 10 BAL fluid samples, respectively, obtained from patients without radiological evidence of IPA, and 5 and 2 of 35 BAL fluid samples, respectively, obtained from nonneutropenic patients. This preliminary investigation suggests that GM may be detected by ELISA in BAL fluid samples from patients at risk of IPA, but that monitoring of serum GM levels may allow for the earlier diagnosis of IPA. However, further evaluation in prospective studies is required.

Sandwich enzyme-linked immunosorbent assay compared with Pastorex latex agglutination test for diagnosing invasive aspergillosis in immunocompromised patients

The performance of a direct sandwich enzyme-linked immunosorbent assay (ELISA) for detecting Aspergillus galactomannan was compared with that of the Pastorex Aspergillus antigen latex agglutination (LA) test by using 532 serum samples from 61 patients at risk for invasive aspergillosis. The ELISA gave positive results earlier in the course of infection than did the LA test. A sensitivity of 70% and a specificity of 86% were obtained for the LA test and corresponding values of 90 and 84% were obtained for the ELISA when a series of serum samples was employed.

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.

Invasive aspergillosis in systemic lupus erythematosus

Invasive aspergillosis is seldomly described in systemic lupus erythematosus. We present two cases of aspergillosis and review 21 cases reported between 1957 and 1994. The typical clinical presentation is fever and cough in a hospitalized SLE patient previously treated with corticosteroids, immunosuppressors, and broad-spectrum antibiotics. Unlike aspergillosis in other conditions, granulocytopenia is uncommon. Chest radiographs show diffuse or patchy infiltration of lung fields. Diagnosis was suspected premortem in 2 patients. Aspergillus fumigatus was identified or isolated in sputum or parenchimal tissues in the majority of cases. Twenty-two patients died (95%). The finding of hyphae in the sputum of a systemic lupus erythematosus patient with a suggestive clinical picture should lead to bronchoscopy, bronchoalveolar lavage, and lung biopsy. Proof of diagnosis will come from the demonstration of hyphae in tissues and isolation of aspergillus from tissue cultures. Long-term therapy with amphotericin B alone or in combination with fluorocytosine or itraconazole may help improve survival.

Use of the Pastorex aspergillus antigen latex agglutination test for the diagnosis of invasive aspergillosis

AIMS

To evaluate the Pastorex aspergillus antigen latex agglutination test for the diagnosis of invasive aspergillosis in patients undergoing liver or bone marrow transplantation.

METHODS

Serum samples were taken at least twice weekly post-transplant and tested for Aspergillus antigen. Latex agglutination test results were compared with microbiological examination of respiratory, urine and bile specimens. Serum samples from liver transplant patients were also tested for antibodies to Aspergillus fumigatus by counter immunoelectrophoresis.

RESULTS

Eight of the 91 patients studied developed invasive aspergillosis. Positive latex agglutination tests were obtained in eight of 187 (4.3%) serum samples from four of these eight patients. The other four patients with invasive aspergillosis gave consistently negative latex agglutination tests. A positive latex agglutination test was the first indication of invasive aspergillosis in two patients; these patients were already on amphotericin B. Positive latex agglutination tests were the only evidence of invasive aspergillosis in one patient who subsequently died of the infection. False positive latex agglutination tests were obtained in five of 83 (6%) patients with no evidence of invasive aspergillosis and misleading positive cultures seen in nine of 83 (10.8%). No antibodies were detected in three of four liver transplant patients with invasive aspergillosis. Conversely, antibodies were detected in 63 of 262 (24%) serum samples from 43 liver transplant patients with no evidence of invasive aspergillosis; one of these patients had an antibody titre of 1:2 on four separate occasions.

CONCLUSIONS

The Pastorex aspergillus antigen latex agglutination test, when used alone, lacks sensitivity and specificity for the early diagnosis of invasive aspergillosis. A diagnosis was made in all patients with invasive aspergillosis when both culture and antigen tests were performed although using these criteria a false positive diagnosis would have been made in 13 of 83 (15.6%) patients. Microbiological and serial serological investigations for antigen should both be performed and the results considered in conjunction with radiological and clinical evidence.

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.

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.

Retrospective evaluation of a latex agglutination test for diagnosis of invasive aspergillosis in immunocompromised patients

A commercial latex agglutination (LA) test for the detection of circulating Aspergillus galactomannan was evaluated in sera obtained from 121 immunocompromised patients, including 19 with proven invasive pulmonary aspergillosis. Patient urine (the specimen of choice for detection of galactomannan) was not tested with the LA test as 34 of 81 specimens from controls gave false-positive results. The sensitivity (95%), specificity (90%) and negative predictive value (99%) of the LA test were similar to previously published results obtained with two EIAs. However, the positive predictive value was only 67% compared to > or = 95% obtained with the EIAs. In addition, the LA test was also of less value than the EIAs in predicting the onset of invasive pulmonary aspergillosis. It was the earliest indicator of infection in only 1 of 19 proven cases.

Aspergillus antigenuria compared to antigenemia in bone marrow transplant recipients

The detection of galactomannan antigen in urine was investigated in 26 bone marrow transplant recipients using an Aspergillus latex agglutination test (Pastorex). After modification of the method, which was originally devised for serum testing, the detection limit in native urine was approximately 20 ng/ml. Antigen was found in 79 (36.4%) of 217 serial urine samples, compared to 40 (11.8%) of 340 serum samples. As a rule, antigenuria preceded antigenemia and was more persistent. The sensitivity, specificity, positive predictive value and negative predictive value of antigenuria for autopsy-proven aspergillosis and clinically suspected Aspergillus infection were 57%, 53%, 31% and 77%, respectively, while those of antigenemia were 43%, 53%, 25% and 71%. It is concluded that urine testing is more reliable than serum testing for the detection of Aspergillus galactomannan. The detection of antigen, however, whether in serum or in urine, allows no clear distinction between Aspergillus infection and exposure to non-infectious Aspergillus antigens.

New cause for false-positive results with the Pastorex Aspergillus antigen latex agglutination test

The Pastorex Aspergillus antigen test for detection of Aspergillus galactomannan antigen in the sera of patients with invasive aspergillosis is used in many clinical laboratories. A serum sample contaminated with Penicillium chrysogenum gave a strongly positive reaction (1:128) which was heat stable, was not eliminated by pronase treatment, and was not detected by a normal rabbit globulin control. This observation was shown to be due to cross-reactions of the monoclonal antibody EB-A2 used by the kit with several airborne fungi likely to contaminate serum samples, including Penicillium chrysogenum, Cladosporium herbarum, Acremonium species, Alternaria alternata, Fusarium oxysporum, Wangiella dermatitidis, and Rhodotorula rubra.

Typing of Aspergillus species and Aspergillus fumigatus isolates by interrepeat polymerase chain reaction

Polymerase chain reaction amplification of repetitive DNA motifs allows discrimination of Aspergillus species. In a preliminary survey, the DNA fingerprints appear to be identical when isolates of Aspergillus fumigatus are compared. When a primer deduced from a prokaryotic repeat motif is used, Aspergillus fumigatus isolates originating from different patients or different anatomical locations can be typed individually.