Value of the Cand-Tec Candida antigen assay in the diagnosis and therapy of systemic candidiasis in high-risk patients

Micafungin versus fluconazole for prophylaxis against fungal infections in premature infants

BACKGROUND

We conducted a comparative clinical study to evaluate the prophylactic effects of micafungin (MCFG) and fluconazole (FLCZ) on the incidence of fungal infections in extremely low-birthweight infants who were born at a gestational age of less than 26 weeks and weighed less than 1000 g.

METHODS

With a combination of enteral administration of miconazole (6 mg/kg/day), FLCZ and MCFG were administered intravenously at a dose of 5 mg/kg/day and 3 mg/kg/day, respectively. The prophylaxis was classified as a failure when fungal infections were identified within the first 21 days after birth.

RESULTS

The prophylaxis was successful in seven of 18 cases (39%) in the FLCZ group and 15 of 21 cases (71%) in the MCFG group, indicating that the success rate was significantly higher in the latter group.

CONCLUSION

MCFG was superior to FLCZ as prophylaxis against fungal infections in extremely low-birthweight infants.

Intact autocrine activation and cytokine production by PMNs from injured adults with elevated Candida antigen titres

Injured patients with Candida antigen titres have increased mortality due to sepsis. Polymorphonuclear leucocytes (PMNs) from injured patients with elevated Candida antigen titres demonstrate impaired function against Candida albicans growth when compared with PMNs from injury matched controls. To determine if PMN dysfunction is global, PMNs from patients with positive Candida antigen titres were evaluated for their ability to activate the anticandidal function of normal PMNs (autocrine activation) and to produce tumour necrosis factor (TNF) and interleukin 8 (IL8), known activators of PMN anticandidal function, this study demonstrates that the PMN dysfunction is not global, as PMN cytokine production and autocrine activation remain intact.

Serologic response to cell wall mannoproteins and proteins of Candida albicans

The cell wall of Candida albicans not only is the structure in which many biological functions essential for the fungal cells reside but also is a significant source of candidal antigens. The major cell wall components that elicit a response from the host immune system are proteins and glycoproteins, the latter being predominantly mannoproteins. Both the carbohydrate and protein moieties are able to trigger immune responses. Although cell-mediated immunity is often considered to be the most important line of defense against candidiasis, cell wall protein and glycoprotein components also elicit a potent humoral response from the host that may include some protective antibodies. Proteins and glycoproteins exposed at the most external layers of the wall structure are involved in several types of interactions of fungal cells with the exocellular environment. Thus, coating of fungal cells with host antibodies has the potential to influence profoundly the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins for host ligands. In this review, the various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo are examined. Although a number of proteins have been shown to stimulate an antibody response, for some of these species the response is not universal. On the other hand, some of the studies demonstrate that certain cell wall antigens and anti-cell wall antibodies may be the basis for developing specific and sensitive serologic tests for the diagnosis of candidasis, particularly the disseminated form. In addition, recent studies have focused on the potential for antibodies to cell wall protein determinants to protect the host against infection. Hence, a better understanding of the humoral response to cell wall antigens of C. albicans may provide the basis for the development of (i) effective procedures for the serodiagnosis of disseminated candidiasis and (ii) novel prophylactic (vaccination) and therapeutic strategies for the management of this type of infection.

Assessment of detection of Candida mannoproteinemia as a method to differentiate central venous catheter-related candidemia from invasive disease

The proper management of candidemic patients is controversial because of the difficulties of an early differentiation of central venous catheter (CVC)-related candidemia from deep-seated invasive Candida infection. In particular, more information on possible markers of invasive disease is needed. We performed a retrospective, pilot investigation to assess the diagnostic potential of a dot immunobinding assay for Candida mannoprotein antigen in serial serum samples from 31 candidemic patients in the setting of hematologic malignancy. Mannoproteinemia (antigenemia) was detected in 1 of 14 (7.1%) patients with transient or CVC-related candidemia and in 13 of 17 (76.5%) patients with non-CVC-related persistent candidemia. Of the 11 subjects of this latter group with documented tissue invasion, 10 (91%) were antigenemic. The patients belonging to the different categories did not significantly differ in the duration of candidemia, nor was there any significant difference among the different groups of subjects either in the number of serum samples examined or in their collection time during candidemia. The day of the first antigenemic sample during candidemia greatly varied among subjects with invasive infection, although on average mannoproteinemia was detectable by the first week of candidemia. In summary, our data demonstrate a correlation between mannoproteinemia and tissue invasion by Candida spp. in candidemic patients and suggest that mannoprotein detection by our method has a potential for the diagnosis of invasive candidiasis in these subjects.

Characterization of specific anti-Candida IgM, IgA and IgE: diagnostic value in deep-seated infections

The proposed serological diagnosis of systemic Candida infections is based on a microplate immunocapture technique detecting IgM, IgA and IgE anti-Candida antibodies. Activity is revealed with a suspension of human erythrocytes sensitized with somatic antigen of Candida albicans, and is quantified on an automated plate reader. The sera were obtained from patients with deep-seated (n = 56) and superficial (n = 193) candidosis. We compared this immunological method with a combination of indirect immunofluorescence and co-immunoelectrodiffusion. The immunocapture method was more sensitive (80.4% vs. 48.2% with indirect immunofluorescence and 58.9% with co-immunoelectrodiffusion), and often provided the diagnosis at an earlier stage, with clear therapeutic advantages. The IgA isotype was a particularly valuable marker of deep-seated Candida infections.

Fungal infection in surgical patients

Invasive fungal infections have become a major source of morbidity and mortality in the modern surgical intensive care unit. Patients at risk for invasion and dissemination are common, and are not as ill as thought previously. Severity of illness (APACHE II score > 10, ventilator use for >48 hours), antibiotics, central venous lines, total parenteral nutrition, burns, and immunosuppression are the most common risk factors. Recognition of these risk factors should arouse a high index of suspicion for the diagnosis of invasion or dissemination. Unfortunately, laboratory tests alone lack sensitivity and specificity. Therefore, the diagnosis of invasion and dissemination in the majority of cases requires the acquisition and proper interpretation of clinical evidence. Once the diagnosis is made, early systemic treatment is warranted. Reported toxicity and efficacy supports the use of fluconazole for most patients with invasive fungal infections. However, for the most critically ill patients amphotericin B remains the treatment of choice.

Prospective evaluation of Candida antigen and antibody assays for detection of Candida infections in children with malignant disease

The clinical efficacy of assays for Candida albicans antigens by latex agglutination and for antibodies by indirect haemagglutination were prospectively evaluated in the diagnosis of invasive Candida infections in 38 children suffering from acute leukaemia or other malignant disease. The controls were 74 other patients without any malignancy; 72 of these had no signs or symptoms of fungal infections, but 2 had an invasive C. albicans infection. During a period of 21 months, 302 serum samples were tested by both assays, and the results were compared with clinical and other microbiological data. Invasive fungal infection was diagnosed on clinical grounds in 2 of the immunocompromised children, and periodic gut colonization was demonstrated in 11 of 36 (31%) children in this group. Positive Candida antigen was detected in 14 patients (37%) and a positive antibody titre in 7 patients (18%). Colonization was not correlated with antigen or antibody titre. Compared with the presence of invasive fungal infection, the antibody assay detected all four infections, whereas the antigen assay detected one of the two C. albicans septicaemias. Although the Candida antibody assay performed well, a detectable change in antibody titres appeared only slowly. Thus it was of no clinical help when antifungal treatment was to be considered. Follow-up of antibody titres, however, gave confirmation of the presence of fungal infection as well as the response to antifungal treatment.

Orointestinal yeast colonization of paediatric bone marrow transplant recipients: surveillance by quantitative culture and serology

We quantitatively studied the orointestinal yeast colonization of 15 consecutive paediatric patients who underwent 16 bone marrow transplantations (BMT). Cultures were performed initially, longitudinally weekly during the period of aplasia (in-patient treatment) and, if possible, also during out-patient follow-up. With one exception, all patients received fluconazole as antifungal prophylaxis. Patients remained free of yeasts during the complete observation period only in six out of 16 cases (38%). Non-albicans species of Candida were isolated in six out of 16 cases (38%), mainly C. glabrata (five out of 16; 31%). All of these patients had undergone allogeneic BMT. In one case, there was indirect evidence of systemic invasion by C. glabrata. Even combined prophylaxis with fluconazole and and amphotericin B suspension could not reliably prevent yeast colonization but this combination at present appears to be the optimal regime. Regular concomitant Candida serology (determination of specific antibodies by three methods) proved to be a valuable additional surveillance method.

Evaluation of enzyme immunoassay for Candida cytoplasmic antigens in neutropenic cancer patients

A Candida albicans cytoplasmic antigen enzyme immunoassay (CACP antigen EIA) was developed with antibodies raised against antigens prepared from yeast cells grown under standardized growth conditions. The C. albicans components reactive in the EIA were shown to be predominantly proteins with associated carbohydrates. Denaturing gel electrophoresis revealed the presence of five major CACP proteins with molecular weights between 36,000 and 44,000. The clinical usefulness of the CACP EIA was evaluated by retrospective blinded measurement of 89 serum samples from 31 granulocytopenic patient episodes. Twice-weekly surveillance cultures, sequential serum samples (approximately once per week or with change of the clinical course), and standard diagnostic criteria of fungal infection were used to categorize patients. The sensitivity and specificity of the CACP assay on the basis of serum samples were 82 and 100%, respectively (67 and 100% on the basis of patient episodes). The positive and negative predictive values were 100 and 97% for serum (100 and 93% for patient episodes). By comparison, the CANDTEC assay had low sensitivity (33%) and poor positive predictive values (50%). The CACP EIA may be a useful test suitable for further evaluations as a method for the diagnosis of invasive Candida infection in neutropenic cancer patients.

Diagnosis of systemic candidiasis by enzyme immunoassay detection of specific antibodies to mycelial phase cell wall and cytoplasmic candidal antigens

Diagnosis of systemic Candida infections was attempted by the use of an enzyme-linked immunosorbent assay (EIA) to detect IgG antibodies towards cell wall-bound and cytoplasmic candidal antigens. Cell wall antigens were sequentially solubilized by treatment of germinated blastoconidia of Candida albicans (ATCC 26555 strain) with beta-mercaptoethanol (beta ME extract) and digestion with Zymolyase 20T, a beta-glucanase preparation (Zymolyase extract). Protoplasts obtained after treatment with Zymolyase were osmotically lysed (cytoplasmic antigens). Sera were obtained from patients with systemic (n = 28) and superficial (n = 46) candidiasis. Control sera were obtained from normal healthy individuals (n = 31) and from hospitalized patients at low (n = 36) and at high (n = 13) risk of developing systemic candidiasis yet showing no symptoms of candidal infection. Detection of antibodies in crude sera samples by EIA using all of these antigenic extracts was highly specific (98-100%), but sensitivity of the method was low (3.5-17.8%). However, adsorption of sera with latex microspheres coated with purified Candida mannan in order to selectively remove anti-mannan antibodies prior to EIA improved the diagnostic efficiency of this test. Improvement was particularly noticeable when the beta ME extract was used as antigenic preparation, yielding a sensitivity of 89.2% and a specificity of 98.6%.

Diagnosis of invasive mycoses in severely immunosuppressed patients

In compromised patients, invasive mycoses are being observed at an increasing frequency and with a broadening spectrum of causative fungi. The rapid and definitive diagnosis of such opportunistic mycoses requires the synoptical consideration of predisposing clinical conditions, of culture isolates, and of the results of nonculture techniques. At present, the latter comprise the monitoring of specific antibodies and of fungal antigens, and the microscopical examination of suspected biopsies. The validity of the individual techniques (e.g., the monitoring of antibodies or antigens) varies with individual mycoses. Alternative methods for monitoring fungal metabolites or nucleic acids are still in the developmental stage. Particularly the amplification of DNA by the polymerase chain reaction (PCR) has a high diagnostic potential. However, at present, it is uncertain whether PCR allows the necessary distinction between colonization and truly invasive infection, and whether PCR can be simplified sufficiently to allow the continuous surveillance of high-risk patients.

Diagnosis of invasive candidiasis by a dot immunobinding assay for Candida antigen detection

A dot immunobinding assay which uses a polyclonal rabbit anti-Candida immunoglobulin G as the primary antibody and colloidal gold coated with goat anti-rabbit immunoglobulin G as the secondary antibody for the detection of Candida cytoplasmic antigens is described. It was able to detect as little as 1 ng of total Candida protein per ml when a cytoplasmic extract of Candida albicans was seeded into buffer and 10 ng/ml when the same extract was seeded into pooled human serum. Serial serum samples from four groups of patients were assayed for Candida antigen: (i) 22 patients with candidemia, (ii) 16 patients at high risk for invasive candidiasis, (iii) 3 patients with other deep mycoses, and (iv) 50 hospitalized patients at low risk for serious Candida infection. Of the 22 candidemic patients, 19 had invasive candidiasis and 3 had transient candidemia. Antigenemia was detected in 16 of the 19 patients with invasive candidiasis (including patients with C. albicans, Candida tropicalis, Candida glabrata, Candida krusei, and Candida parapsilosis) and in 4 of 16 patients at high risk for invasive candidiasis. There was no detectable antigen in 12 high-risk control patients, 3 patients with transient candidemia, 3 patients with other deep mycoses, and 50 relatively low-risk patients. The sensitivity for detecting invasive disease in candidemic patients and specificity for all patients studied were 84.2 and 94.4%, respectively. The positive predictive value was 80%; the negative predictive value was 95.7%. The sensitivity for neutropenic patients with invasive disease was 85.7%. This assay is rapid and accurate and appears to be useful in identifying candidemic patients with invasive candidiasis.

Laboratory aids in the diagnosis of invasive candidiasis

The laboratory diagnosis of candidiasis continues to be problematic; however, there have been several advances in the past decade which promise to enhance our ability to identify patients at high risk for infection and/or to document invasive candidiasis in critically ill and immunocompromised patients. The introduction of commercially available biphasic blood culture medium and subsequently the lysis-centrifugation procedure has markedly improved the ability of laboratories to detect fungemia. Although serologic methods have not been very successful in diagnosing candidiasis in immunocompromised patients, several antigen detection methods are now under investigation. In addition, detection of fungal metabolites such as D-arabinitol remains promising. Finally, application of the techniques of molecular biology for typing and detection of fungal pathogens has expanded our understanding of candidal infections and may offer the most sensitive and specific means of diagnosing invasive candidiasis.

Retrospective evaluation of two latex agglutination tests for detection of circulating antigens during invasive candidosis

Two latex agglutination tests for the detection of Candida antigens, Pastorex Candida (Sanofi Diagnostics Pasteur, Marnes-la-Coquette, France) and Cand-Tec (Ramco Laboratories, Inc., Houston, Tex.), were applied to 79 serum samples from 19 patients who were retrospectively selected on the basis of mycological and clinical evidence of C. albicans infection and the availability of serial serum samples taken near the date of a positive culture. The specificity in 60 control individuals was 100% for Pastorex and 98.3% for Cand-Tec. The tests scored positive for 10 (52.6%) and 9 (47.4%) patients, respectively. Pastorex detected antigen in only 3 of 12 patients (25%) with positive antibody detection tests, but was positive for all 7 patients (100%) who produced no or a low antibody response, suggesting that the test performs better in the absence of antibodies. However, the sensitivity of Pastorex also increased with the number of samples available per patient, which was lower for high-antibody-responder patients (2.8 versus 5.7). If the patients who provided only one or two serum samples were eliminated, the sensitivity of Pastorex rose to 76.9%. For the Cand-Tec, the sensitivity was not related to the presence of antibodies, nor was it related to the number of samples per patient. The observed antigenemia was transient with both Pastorex and Cand-Tec. Only 12.5% of the positive reactions occurred on the same serum sample, confirming that the two tests react with different antigens. A positive antigen test preceded other diagnostic indications for 6 of 10 Pastorex-positive patients and 5 of 9 Cand-Tec-positive patients.

Evaluation of a Candida antigen detection method (Cand-Tec): Experience from a university teaching hospital

The usefulness of a rapid latex agglutination method for the detection of Candida antigen (Cand-Tec; Ramco Laboratories. Texas) was retrospectively assessed in a university teaching hospital over a one year period. Patients were enrolled when the managing physician requested Cand-Tec testing for confirmation of possible invasive candidal infection. The majority of patients were critically ill; 56% were in the intensive care unit, and 30% subsequently died. Analyses were available from 79 patients and 125 samples. Thirty-three patients were diagnosed as having either definite invasive candidiasis or a high probability of infection based upon clinical, microbiological and tissue criteria. The sensitivity and specificity of Candida antigen detection was determined for doubling titres ≥1:4 to ≥1:16. If a titre of ≥1:4 was used as the diagnostic cut-off level for definite candidal infection, overall sensitivity and specificity were 77% and 69%, respectively, while the positive predictive value was 48%, and the negative predictive value 89%. When patients with a high probability of invasive candidal infection were included in analyses for a cut-off titre of ≥1:4, overall sensitivity and specificity were 70% and 69%, respectively, while the positive predictive value was 68%, and the negative predictive value 71%. The usefulness of the Cand-Tec test was not improved further for any subgroup of patients (including those in the intensive care unit), nor by following serial titres in individual patients. In this experience, the Cand-Tec test did not add enough information to include definitively or exclude invasive candidiasis in this high risk general patient population.

Diagnosis of disseminated candidiasis in hospitalized patients using the Cand-Tec latex agglutination assay

A total of 1,303 sera from 202 patients at risk for disseminated candidiasis were analyzed for the presence of Candida antigen using a commercially available latex agglutination test (Cand-Tec). Twenty-three patients had disseminated candidiasis documented by positive blood cultures, deep biopsy culture and histopathology or autopsy. Six patients had transient candidemia, 15 patients had candiduria, 62 patients were not colonized yet treated empirically with amphotericin B, and 46 patients were not colonized and not treated with amphotericin B. The sensitivity and specificity of the Candida antigen test for the diagnosis of disseminated candidiasis was 87% and 36% (threshold titer of greater than or equal to 1:2), 70% and 60% (greater than or equal to 1:4), and 30% and 85% (greater than or equal to 1:8), respectively. In contrast to previous studies we were unable to demonstrate a prognostic role for the Candida antigen test in patients with documented disseminated candidiasis. The lack of sensitivity and specificity of the Cand-Tec Candida antigen test precludes its use in the diagnosis of disseminated candidiasis.

Monoclonal antibody-gold silver staining dot assay for the detection of antigenaemia in candidosis

A monoclonal antibody (Mab), designated 5B2, reacting with cell wall mannoproteins of Candida albicans has been purified and coupled to colloidal gold. The ability of the gold conjugated Mab to detect C. albicans antigens in serum during infection has been assessed in a dot immunobinding assay involving an immunogold silver enhancement procedure (GSS). A double blind study was made with sera from 140 guinea pigs, including 40 control animals and 100 infected intravenously with C. albicans. Sera from infected animals were collected either 2 days (4 animals), 15 days (9 animals), or 21 days (87 animals) after inoculation. The overall sensitivity, specificity and positive predictive value of the test were 89, 95, and 98%, respectively. However, differences were encountered in the ratio of positive tests in relation to duration of the infection. Mab-GSS dot immunobinding has also been applied, together with Mab co-counterimmunoelectrophoresis on successive sera from 2 patients who recovered from clinically and mycologically proven episodes of systemic candidosis. It was demonstrated that both patients synthesized antibodies against glycoproteins sharing the 5B2 epitope, which was initially present transiently in their sera.

The use of biotyping and DNA fingerprinting in typing Candida albicans from hospitalized patients

The application of typing procedures for the purpose of strain differentiation among isolates of Candida albicans obtained from hospitalized patients has been limited. We have applied biotyping and DNA restriction fragment analysis (DNA fingerprinting) by using EcoRI to the study of C. albicans isolates obtained from hospitalized patients. A total of 68 isolates from 15 patients were studied. Thirteen subtypes were identified by biotyping, 8 by DNA fingerprinting, and 21 by a combination of the biotyping and DNA fingerprinting approaches (composite subtype). Both techniques were highly reproducible. In examining the strain variation among isolates obtained from multiple anatomic sites over time, we found that similar, if not identical, strains were recovered from the oropharynx, urine, stool, and blood in a given patient, and these strains persisted. Only rarely did two patients share the same composite subtype suggesting sporadic nosocomial transmission. The combination of biotyping and DNA fingerprinting improved strain discrimination compared to either method alone. Further investigation with these and other epidemiologic typing methods will be necessary to enhance the understanding of the epidemiology and pathogenesis of candidiasis in hospitalized patients.

Nonvalue of antigen detection immunoassays for diagnosis of candidemia

We evaluated the Cand-Tec (Ramco Laboratories Inc., Houston, Tex.) and LA-Candida antigen detection system (Immuno-Mycologics Inc., Norman, Okla.) tests as possible rapid alternatives to blood cultures for the identification of patients with candidemia. Tests were performed on sera from (i) 33 patients with candidemia, (ii) 82 patients with fever and risk factors for invasive candidiasis, and (iii) 13 healthy controls. A total of 21 patients had no evidence of invasive candidiasis, as determined by clinical course, blood culture, and/or autopsy; results for 61 patients were indeterminate regarding the presence of invasive candidiasis, or else the patients had invasive candidiasis with organ involvement. By using a threshold positive Cand-Tec titer of greater than or equal to 1:4, the sensitivity in candidemic patients was 49%; the specificity was 43% (patients with true-negative results had neither candidemia nor other evidence of invasive candidiasis). Coexistent disseminated candidiasis in some candidemic patients may have accounted for some positive Cand-Tec tests and possible overestimation of the sensitivity of the test for candidemia. Cand-Tec test results were negative for healthy controls. All test results obtained by the LA-Candida antigen detection system assay were negative. Our findings indicate that neither of these assays reliably identifies patients with candidemia.