False-positive reactions in the latex agglutination test for Cryptococcus neoformans antigen

Evolution of Laboratory Diagnostics for Cryptococcosis and Missing Links to Optimize Diagnosis and Outcomes in Resource-Constrained Settings

Cryptococcal meningitis is one of the leading causes of death in sub-Saharan Africa among patients with advanced HIV disease. Early diagnosis is crucial in improving treatment outcomes. Despite advances and the availability of modern and point-of-care diagnostics for cryptococcosis, gaps still exist in resource-constrained settings, leading to unfavorable treatment outcomes. Here, we review the current outstanding issues or missing links that need to be filled to optimize the diagnosis of cryptococcosis in resource-constrained settings to improve treatment outcomes. We highlight the evolution of cryptococcosis diagnostics; the roles of early fungicidal activity, cryptococcal antigen titers, antifungal susceptibility testing, and therapeutic drug monitoring; and the missing links to optimize diagnosis and outcomes, including practical recommendations.

Evaluation of a Cryptococcal Antigen Lateral Flow Assay and Cryptococcal Antigen Positivity at a Large Public Hospital in Atlanta, Georgia

BACKGROUND

Cryptococcus neoformans is a major cause of morbidity and mortality among human immunodeficiency virus (HIV)-infected persons worldwide, and there are scarce recent data on cryptococcal antigen (CrAg) positivity in the United States We sought to determine the frequency of cryptococcal disease and compare the performance of a CrAg lateral flow assay (LFA) versus latex agglutination (LA) test.

METHODS

All patients from Grady Health System in Atlanta who had a serum or cerebrospinal fluid (CSF) sample sent for CrAg testing as part of clinical care from November 2017 to July 2018 were included. Percentage positivity and test agreement were calculated.

RESULTS

Among 467 patients, 557 diagnostic tests were performed; 413 on serum and 144 on CSF. The mean age was 44 years, and most were male (69%) and had HIV (79%). Twenty-four (6.4%, 95% confidence interval [CI] = 4.1-9.4) patients were serum CrAg positive, and 8 (5.8%, 95% CI = 2.6-11.2) individuals tested positive for CSF CrAg. Although overall agreement between the LA and LFA was substantial to high for CSF (κ = 0.71, 95% CI = 0.51-0.91) and serum (κ = 0.93, 95% CI = 0.86-1.00), respectively, there were important discrepancies. Five patients had false-positive CSF LA tests that affected clinical care, and 4 patients had discordant serum tests.

CONCLUSIONS

We found a moderately high proportion of cryptococcal disease and important discrepancies between the LA test and LFA. Clinical implications of these findings include accurate detection of serum CrAg and averting unnecessary treatment of meningitis with costly medications associated with high rates of adverse events.

Cryptococcus gattii infections

Understanding of the taxonomy and phylogeny of Cryptococcus gattii has been advanced by modern molecular techniques. C. gattii probably diverged from Cryptococcus neoformans between 16 million and 160 million years ago, depending on the dating methods applied, and maintains diversity by recombining in nature. South America is the likely source of the virulent C. gattii VGII molecular types that have emerged in North America. C. gattii shares major virulence determinants with C. neoformans, although genomic and transcriptomic studies revealed that despite similar genomes, the VGIIa and VGIIb subtypes employ very different transcriptional circuits and manifest differences in virulence phenotypes. Preliminary evidence suggests that C. gattii VGII causes severe lung disease and death without dissemination, whereas C. neoformans disseminates readily to the central nervous system (CNS) and causes death from meningoencephalitis. Overall, currently available data indicate that the C. gattii VGI, VGII, and VGIII molecular types more commonly affect nonimmunocompromised hosts, in contrast to VGIV. New, rapid, cheap diagnostic tests and imaging modalities are assisting early diagnosis and enabling better outcomes of cerebral cryptococcosis. Complications of CNS infection include increased intracranial pressure, severe neurological sequelae, and development of immune reconstitution syndrome, although the mortality rate is low. C. gattii VGII isolates may exhibit higher fluconazole MICs than other genotypes. Optimal therapeutic regimens are yet to be determined; in most cases, initial therapy with amphotericin B and 5-flucytosine is recommended.

Rare Association of Severe Cryptococcal and Tuberculosis in Central Nervous System in a case of Sarcoidosis

Sarcoidosis is a multisystem noncaseating granulomatous disease with a propensity for lung, eye, and skin which recently have been proposed that mycobacterium tuberculosis may contribute in its pathogenesis, and rarely involves central nervous system (CNS). Despite CD4+ lymphocytopenia, sarcoidosis by itself does not increase risk of opportunistic infections other than cryptococcosis. Nonetheless, simultaneous association of CNS cryptococcosis and tuberculosis infection remains extremely rare event in immunocompetent states, and has not been reported in sarcoidosis yet. We here presented such a case in a 42 years old man, a known case of sarcoidosis with diagnostic and therapeutic difficulties were encountered in a fourteen-month-long hospitalization period.

Central nervous system infections in cancer patients and hematopoietic stem cell transplant recipients

Central nervous system (CNS) infections in cancer patients present a diagnostic and therapeutic challenge for clinicians. While CNS infections are not frequent complications of cancer, its therapies, or hematopoietic stem cell transplantation, the importance of CNS infections lies in their propensity to result in profound morbidity and substantial mortality in this vulnerable patient population. With an expanding population of patients with malignant disease undergoing more potent and aggressive therapies and with the advent of newer immunomodulatory agents, the incidence of CNS infectious complications is likely to rise. This chapter will summarize the clinical and diagnostic evaluation of potential infections of the CNS in these patients and will discuss particular pathogens of interest with regard to this at-risk patient population.

Fungal diagnostics: review of commercially available methods

Fungi and yeasts are critical causes of acute infection. As such, the detection and identification of these organisms are crucial in the diagnosis of affected patient populations. There is a vast array of commercial tests currently available for diagnostic purposes. These vary from traditional culture and biochemical methods to advanced multiparameter molecular tests. Recent technological advances have driven the development of rapid tests which are complementing and in some cases replacing the more traditional methods of detection. Irrespective of the method used the ultimate goal is timely detection of the infectious agent allowing appropriate treatment and improved outcome for the patient.

Detection of Cryptococcus by conventional, serological and molecular methods

The rising incidence of cryptococcosis in India is posing a serious threat. Due to lack of sensitive methods for diagnosis, high morbidity and mortality are associated with the disease. Early diagnosis is essential to prevent serious complications. Therefore, we attempted to find highly sensitive and specific detection methods. A comparative evaluation of the detection of cryptococcosis was done by conventional (direct microscopy and culture) and rapid diagnostic [latex agglutination test (LAT), enzyme immunoassay (EIA) and PCR] methods. The study was done on 359 samples from 52 positive patients and 30 negative controls in an Indian set-up. Evaluation was done for cerebrospinal fluid (CSF), serum and urine separately. The diagnostic value of the tests was assessed in pre-treatment samples, and follow-up tests were also done on samples obtained after initiation of treatment. PCR had the highest sensitivity, followed by EIA and LAT, both before and after treatment. The positive detection by LAT, EIA and PCR was the longest in CSF (>90 days), followed by serum (∼65 days) then urine (∼45 days) after initiation of treatment. Our results indicated that the sensitivity and specificity of PCR and EIA were comparable in urine, CSF and serum for diagnosis of cryptococcosis.

Cryptococcosis

In the past 2 decades, Cryptococcus has emerged in its clinical significance and as a model yeast for understanding molecular pathogenesis. C neoformans and C gattii are currently considered major primary and secondary pathogens in a wide array of hosts that are known to be immunocompromised or apparently immunocompetent. A recent outbreak of C gattii infections further underscores the clinical importance of the yeast through its epidemiology and pathogenicity features. With an enlarging immunosuppressed population caused by HIV infection, solid organ transplantation, and clinical use of potent immunosuppressives, such as cancer chemotherapy, monoclonal antibodies, and corticosteroids, this fungus has become a well-established infectious complication of modern medicine. This article examines current issues in cryptococcal infections, including new classification, epidemiology, pathogenesis, and specific clinical aspects.

Inactivated pronase as the cause of false-positive results of serum cryptococcal antigen tests

Four patients who had acquired immunodeficiency syndrome and who were evaluated for headache within a 3-week period had false-positive results of serum cryptococcal antigen tests. This cluster of false-positive test results appeared to be due to inactivation of the pronase vial in the test kit, a cause that has not been reported previously.

Utility of routine testing of bronchoalveolar lavage fluid for cryptococcal antigen

All cryptococcal antigen (CrAg) testing performed at our institution between 1989 and 1994 was reviewed for utility of routinely testing of bronchoalveolar lavage fluid (BAL) for this antigen. Forty-two of 1,506 BAL specimens were positive. Seventeen of these were felt to represent false positives (sensitivity, 71%; positive predictive value, 0.59). The data on CrAg in cerebrospinal fluid and serum and the fungal culture and histological results of BAL specimens did not support continued, routine testing of BALs for CrAg to diagnose cryptococcosis.

Cryptococcosis in the era of AIDS--100 years after the discovery of Cryptococcus neoformans

Although Cryptococcus neoformans and cryptococcosis have existed for several millennia, a century has passed since the discovery of this encapsulated yeast and its devastating disease. With the advent of the AIDS pandemic, cryptococcal meningitis has emerged as a leading cause of infectious morbidity and mortality and a frequently life-threatening opportunistic mycosis among patients with AIDS. Both basic and clinical research have accelerated in the 1990s, and this review attempts to highlight some of these advances. The discussion covers recent findings, current concepts, controversies, and unresolved issues related to the ecology and genetics of C. neoformans; the surface structure of the yeast; and the mechanisms of host defense. Regarding cell-mediated immunity, CD4+ T cells are crucial for successful resistance, but CD8+ T cells may also participate significantly in the cytokine-mediated activation of anticryptococcal effector cells. In addition to cell-mediated immunity, monoclonal antibodies to the major capsular polysaccharide, the glucuronoxylomannan, offer some protection in murine models of cryptococcosis. Clinical concepts are presented that relate to the distinctive features of cryptococcosis in patients with AIDS and the diagnosis, treatment, and prevention of cryptococcosis in AIDS patients.

Elimination of false-positive serum reactivity in latex agglutination test for cryptococcal antigen in human immunodeficiency virus-infected population

We recently tested serum from a human immunodeficiency virus-infected patient for the presence of cryptococcal antigen using the Meridian latex agglutination (LA) test (Cryptococcal Antigen Latex Agglutination System). Two pronase-treated serum specimens from the patient had LA titers of 80 and 160, but the patient had no evidence of cryptococcal disease. The serum was negative for rheumatoid factor, a well-documented cause of false-positive LA reactions. Seven blood culture supernatants from the patient were also LA positive, but were culture negative for cryptococcus. When the sera and blood culture supernatants were treated with 0.01 M 2-beta-mercaptoethanol (2-ME), the agglutinating activity was ablated. Similar results were seen when the sera were tested by two other commercial LA assays. Serum and cerebrospinal fluid specimens from patients with confirmed cryptococcal disease were treated with 2-ME, and the results were compared with those obtained after pronase (sera) or heat (cerebrospinal fluid) inactivation. The titers were identical (n = 56) or within 1 dilution (n = 3). One hundred serum specimens from human immunodeficiency virus-seropositive patients with no known history of cryptococcal disease were examined to determine the frequency of false-positive reactivity in this patient population. Of this group, three were positive following pronase treatment. One remained positive after 2-ME treatment; the remaining two were negative. These data indicate that 2-ME can be used to eliminate nonspecific reactivity in the LA test without affecting true-positive results.

Latex agglutination test negative cryptococcal meningitis in an immuno-competent individual: a case report

We report a case with progressive mental deterioration and persistent low grade fever, who was diagnosed to have cryptococcal meningitis. This case is unique in that the cryptococcal latex agglutination antigen test was consecutively negative. The diagnosis was made by sequential CSF culture.

False-negative cerebrospinal fluid cryptococcal latex agglutination tests for patients with culture-positive cryptococcal meningitis

Three cases of false-negative cerebrospinal fluid latex agglutination test results for patients with culture-positive cryptococcal meningitis are reported. False-negative results occurred in settings of low cryptococcal antigen concentrations in cerebrospinal fluid and were dependent on the latex agglutination test kit used. Investigation of each case revealed that prozone phenomena or interference from bound antibody or protein could not account for the false-negative results.

Evaluation of Gen-Probe's Histoplasma capsulatum and Cryptococcus neoformans AccuProbes

Gen-Probe's DNA probes were evaluated for use in the identification of clinical isolates of Histoplasma capsulatum var. capsulatum and Cryptococcus neoformans. Ninety-five mould-phase fungi were probed, including 41 isolates of H. capsulatum var. capsulatum. Similarly, 98 yeasts, including 42 C. neoformans isolates, were examined by using the C. neoformans DNA probe. In the study, both probes demonstrated 100% specificity and 100% sensitivity. Their use in the clinical laboratory may significantly reduce the time required for definitive identification of fungi.

Evaluation of an enzyme immunoassay for detection of cryptococcal capsular polysaccharide antigen in serum and cerebrospinal fluid

The Premier enzyme immunoassay (Meridian Diagnostics, Inc., Cincinnati, Ohio) was compared with a latex agglutination assay (CALAS; Meridian) for the ability to detect cryptococcal capsular polysaccharide antigen (CrAg) in serum and cerebrospinal fluid (CSF). A total of 594 specimens (471 serum samples and 123 CSF samples) obtained from 430 patients, most of whom were at risk for or had AIDS, were tested in parallel by both systems. Both tests were independently evaluated for their ability to (i) detect CrAg when used as a screening test and (ii) quantitate the CrAg present when used as a titration assay. Chart review to assess clinical outcome after the time of specimen collection was conducted for all patients. When both assays were used as screening assays, 103 serum samples and 18 CSF samples were positive and 356 serum samples and 104 CSF specimens were negative by both assays (97.8% concordance). Thirteen specimens (12 serum samples, 1 CSF sample) gave discrepant screening results. When the tests were used as semiquantitative assays for titer determinations, the CrAg titers determined by the enzyme immunoassay were generally higher than those obtained with the latex agglutination assay. In summary, results obtained with the enzyme immunoassay correlated well with those obtained with the latex agglutination test for screening for the presence of CrAg and for determining the titer of CrAg in serum or CSF.

Evaluation of a commercial enzyme immunoassay for the detection of cryptococcal antigen

A total of 143 cerebrospinal and serum samples, from proven and suspected cases of cryptococcosis, were concurrently examined using a recently introduced enzyme immunoassay (EIA Premier, Meridian Diagnostics, Inc., Cincinnati, OH, USA) and three latex agglutination (LA) procedures (Immunomycologics, Inc., Norman, OK, USA; IBL, Inc., Cranbury, NJ, USA and a non-commercial LA test). Of these 143 specimens, 115 were negative for cryptococcal antigen (CrAg) with the EIA and LA tests. The remaining 28 specimens were evaluated by the LA tests, and all were positive for CrAg (with titres ranging from 1:2 to 1:8192). Of these 28 LA-positive specimens, 26 were also tested by the EIA. This procedure detected CrAg in 23 specimens (88.5%), with antigen levels ranging from 1:4 to 1:266,857. There were 3 LA-positive specimens (tires 1:4 to 1:32) which were negative by the EIA procedure (10.7%). One LA-negative specimen demonstrated CrAg (titre 1:30) by the EIA procedure. The sensitivity of the EIA and LA tests was 85.2 and 100%, respectively. The specificity of the LA test was 100%, whereas that of the EIA was 97%. The agreement among laboratories for testing the specimens with the three LA tests was 100%.