Utility of routine testing of bronchoalveolar lavage fluid for cryptococcal antigen

The SSS revolution in fungal diagnostics: speed, simplicity and sensitivity

INTRODUCTION

Fungal disease has historically presented a diagnostic challenge due to its often non-specific clinical presentations, relative infrequency and reliance on insensitive and time-intensive fungal culture.

SOURCES OF DATA

We present the recent developments in fungal diagnostics in the fields of serological and molecular diagnosis for the most clinically relevant pathogens; developments that have the potential to revolutionize fungal diagnosis through improvements in speed, simplicity and sensitivity. We have drawn on a body of evidence including recent studies and reviews demonstrating the effectiveness of antigen and antibody detection and polymerase chain reaction (PCR) in patients with and without concurrent human immunodeficiency virus infection.

AREAS OF AGREEMENT

This includes recently developed fungal lateral flow assays, which have a low cost and operator skill requirement that give them great applicability to low-resource settings. Antigen detection for Cryptococcus, Histoplasma and Aspergillus spp. are much more sensitive than culture. PCR for Candida spp., Aspergillus spp., Mucorales and Pneumocystis jirovecii is more sensitive than culture and usually faster.

AREAS OF CONTROVERSY

Effort must be made to utilize recent developments in fungal diagnostics in clinical settings outside of specialist centres and integrate their use into standard medical practice. Given the clinical similarities of the conditions and frequent co-infection, further study is required into the use of serological and molecular fungal tests, particularly in patients being treated for tuberculosis.

GROWING POINTS

Further study is needed to clarify the utility of these tests in low-resource settings confounded by a high prevalence of tuberculosis.

AREAS TIMELY FOR DEVELOPING RESEARCH

The diagnostic utility of these tests may require revision of laboratory work flows, care pathways and clinical and lab coordination, especially for any facility caring for the immunosuppressed, critically ill or those with chronic chest conditions, in whom fungal disease is common and underappreciated.

Pulmonary cryptococcosis: A review of pathobiology and clinical aspects

Pulmonary cryptococcosis is an important opportunistic invasive mycosis in immunocompromised patients, but it is also increasingly seen in immunocompetent patients. The main human pathogens are Cryptococcus neoformans and C. gattii, which have a worldwide distribution. In contrast to cryptococcal meningitis, pulmonary cryptococcosis is still underdiagnosed because of limitations in diagnostic tools. It can mimic lung cancer, pulmonary tuberculosis, bacterial pneumonia, and other pulmonary mycoses both clinically and radiologically. Pulmonary nodules are the most common radiological feature, but these are not specific to pulmonary cryptococcosis. The sensitivity of culture of respiratory samples for Cryptococcus is poor and a positive result may also reflect colonisation. Cryptococcal antigen (CrAg) with lateral flow device is a fast and sensitive test and widely used on serum and cerebrospinal fluid, but sera from patients with pulmonary cryptococcosis are rarely positive in the absence of disseminated disease. Detection of CrAg from respiratory specimens might assist the diagnosis of pulmonary cryptococcosis but there are very few data. Molecular detection techniques such as multiplex reverse transcription polymerase chain reaction (RT-PCR) could also provide better sensitivity but these still require validation for respiratory specimens. The first line of treatment for pulmonary cryptococcosis is fluconazole, or amphotericin B and flucytosine for those with central nervous system involvement. Pulmonary cryptococcosis worsens the prognosis of cryptococcal meningitis. In this review, we summarize the biological aspects of Cryptococcus and provide an update on the diagnosis and management of pulmonary cryptococcosis.

Examination of cryptococcal glucuronoxylomannan antigen in bronchoalveolar lavage fluid for diagnosing pulmonary cryptococcosis in HIV-negative patients

We clarified the performance of a cryptococcal glucuronoxylomannan (GXM) antigen test using bronchoalveolar lavage fluid (BALF) samples, in an HIV-negative Japanese population. Between March 2008 and December 2014, we examined cryptococcal GXM antigens in both serum and BALF specimens from 429 cases at Nagasaki University hospital. The diagnoses, underlying diseases, chest computed tomography findings, and cryptococcal GXM antigen test results were retrospectively investigated. Twenty-three patients were confirmed to have pulmonary cryptococcosis, another six were clinically diagnosed with cryptococcosis because they were seropositive for the GXM antigen, and five possible cryptococcosis cases had BALF samples that were positive for the GXM antigen and serum samples that were negative. The test's sensitivities for detecting cryptococcal GXM antigens in serum and BALF samples, for confirmed cases, were 73.9% and 82.6%, respectively, and their respective specificities were 98.5% and 97.8%. Three of the five putative patients with cryptococcosis were treated with antifungal agents; the pulmonary lesions decreased in size in all treated patients. Both the BALF and serum GXM antigen titers showed positive correlations with the lesion sizes; however, the serum antigen titers showed a higher correlation (r = 0.490, P = .0033) than did the BALF titres (r = 0.312, P = .0724). The rate of GXM-positive BALF samples was higher than the rate for serum samples, especially for patients with pulmonary lesion diameters ≤25 mm. Testing for the presence of the cryptococcal GXM antigen in BALF specimens might contribute to the early diagnosis of pulmonary cryptococcosis.

Approach to Fungal Infections in Human Immunodeficiency Virus-Infected Individuals: Pneumocystis and Beyond

Many fungi cause pulmonary disease in patients with human immunodeficiency virus (HIV) infection. Pathogens include Pneumocystis jirovecii, Cryptococcus neoformans, Aspergillus spp, Histoplasma capsulatum, Coccidioides spp, Blastomyces dermatitidis, Paracoccidioides brasiliensis, Talaromyces marneffei, and Emmonsia spp. Because symptoms are frequently nonspecific, a high index of suspicion for fungal infection is required for diagnosis. Clinical manifestations of fungal infection in HIV-infected patients frequently depend on the degree of immunosuppression and the CD4⁺ helper T cell count. Establishing definitive diagnosis is important because treatments differ. Primary and secondary prophylaxes depend on CD4⁺ helper T cell counts, geographic location, and local prevalence of disease.

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.

Nonmolecular methods for the diagnosis of respiratory fungal infections

Diagnosis of invasive fungal pneumonias by conventional culture methods is difficult to assess and often delayed. Nonmolecular fungal markers have emerged as an important adjunctive tool to support their diagnosis in combination with other clinical, radiologic, and microbiological criteria of invasive fungal diseases. Concerns about the sensitivity and specificity of some tests in different patient populations should lead to warnings about their widespread use. None can identify the emerging and particularly deadly fungal pathogens responsible for mucormycosis. The role of nonmolecular fungal markers should be better defined in combination with other microbiological and radiologic tools in preemptive antifungal strategies.

Fungal diagnostics in pneumonia

Fungal pneumonia is increasingly common, particularly in highly immunosuppressed patients, such as solid organ or hematopoietic stem cell transplant recipients, and the diagnosis is evolving. Although standard techniques such as microscopy and culture remain the mainstays of diagnosis, relatively recent advances in serological and molecular testing are important additions to the field. This article reviews the laboratory tools used to diagnose fungal respiratory disease.

Diagnosing invasive fungal disease in critically ill patients

Fungal infections are increasing, with a changing landscape of pathogens and emergence of new groups at risk for invasive disease. We review current diagnostic techniques, focusing on studies in critically ill patients. Microbiological cultures, the current "gold standard", demonstrate poor sensitivity, thus diagnosis of invasive disease in the critically ill is difficult. This diagnostic dilemma results in under- or over-treatment of patients, potentially contributing to poor outcomes and antifungal resistance. While other current diagnostic tests perform moderately well, many lack timeliness, efficacy, and are negatively affected by treatments common to critically ill patients. New nucleic acid-based research is promising.

Cryptococcal lung disease

PURPOSE OF REVIEW

Cryptococcosis is an important opportunistic fungal infection, especially in the immunocompromised patient. Meningitis is the most common manifestation of cryptococcosis; however, cryptococcal lung disease is probably underdiagnosed, and knowledge of epidemiology, diagnosis, and treatment is necessary.

RECENT FINDINGS

Cryptococcal lung disease ranges from asymptomatic colonization or infection to severe pneumonia with respiratory failure. Clinical presentation of pulmonary cryptococcosis is highly variable and often is related to the immune status of the patient. There have been many important clinical trials outlining treatment of cryptococcal meningitis in patients with AIDS, but there is a lack of treatment data available for patients with cryptococcal lung disease. Treatment recommendations for cryptococcal lung disease are made on the basis of host immune status and severity of clinical illness. For less severe disease, fluconazole therapy is recommended. In immunocompromised patients, or those with severe disease, induction therapy with an amphotericin B preparation and flucytosine, followed by fluconazole as consolidation and maintenance therapy, is recommended.

SUMMARY

Cryptococcal lung disease is an important and probably underdiagnosed infection. Knowledge of the epidemiology, diagnostic methodologies, and treatment is needed to ensure good patient outcomes.

Pulmonary fungal infection with yeasts and pneumocystis in patients with hematological malignancy

Invasive fungal infections are an important cause of morbidity and mortality in patients with hematological malignancies, and in particular fungal pneumonia is the main clinical manifestation in this category of patients. The fungal agents responsible for this complication are various, but Aspergillus spp. and other molds such as Zygomycetes or Fusarium spp. represent the most frequently isolated micro-organisms. Less commonly, pneumonia could be due to other 'no-molds' fungal agents such as Candida spp, Cryptococcus spp, or Pneumocystis jirovecii . This review mainly focuses on practical aspects relevant to epidemiology, diagnosis and therapeutic management of the rare cases of pneumonia due to no-molds agents in patients affected by hematological malignancies.

Quantification and assessment of viability of Cryptococcus neoformans by LightCycler amplification of capsule gene mRNA

Cryptococcus neoformans is an opportunistic fungal pathogen. It infects the central nervous system causing meningitis, which is fatal if untreated, especially in AIDS and immunosuppressed patients. In this study a method of quantification and assessment of viability of C. neoformans by LightCycler RT-PCR amplification of the capsule gene mRNA is established. The sequence of primers and probes were derived from C. neoformans capsular CAP10 gene mRNA (GenBank accession number AF144574), and were species specific. Agarose gel electrophoresis analysis of LightCycler RT-PCR product showed a single band of 223 bp in length. In order to develop an internal control a 223 bp exon fragment of capsule mRNA was cloned in the pCR2.1 plasmid vector and RNA was generated by in vitro transcription. To determine the sensitivity of the assay, serial dilutions of in vitro-transcribed RNA with known concentrations and copy numbers, and serially diluted cultures of viable and nonviable C. neoformans were used. Under optimal conditions as little as 0.472 fg of capsule mRNA could be detected, corresponding to 1-10 c.f.u. ml(-1) of the sample. No amplification was observed from up to 10(5) heat/UV radiation-killed yeast cells and RNA of other bacterial and fungal pathogens and human genomic DNA or RNA. The amplification of capsule mRNA represents a sensitive, specific and quantitative means of detection of viable C. neoformans in clinical specimens and can be useful in the evaluation of the therapeutic efficacy of antifungal drugs in the treatment of C. neoformans meningitis.

Utility of testing bronchoalveolar lavage fluid for cryptococcal ribosomal DNA

Bronchoalveolar lavage (BAL) specimens from 88 patients (33 infected with human immunodeficiency virus [HIV], 45 non-HIV immunosuppressed patients and 10 immunocompetent patients with primary pulmonary disease) were analysed for the presence of Cryptococcus neoformans. Staining, culture and an antigen testing were performed, and C. neoformans ribosomal DNA (rDNA) detected using the polymerase chain reaction (PCR). C. neoformans was detected, by staining and culture, in BAL specimens from two HIV-infected patients with pulmonary cryptococcosis, and the antigen test and rDNA assay were also positive in these samples. C. neoformans rDNA was detected by PCR in a non-HIV immunocompromised patient with Pneumocystis pneumonia, whose staining, culture and antigen tests were negative. The antigen test was positive for an immunocompetent patient with sarcoidosis, while staining, culture and the PCR assay were negative. These results do not support routine testing of BAL specimens for C. neoformans rDNA.

Detection of Cryptococcus neoformans DNA in tissue samples by nested and real-time PCR assays

Two PCR protocols targeting the 18S rRNA gene of Cryptococcus neoformans were established, compared, and evaluated in murine cryptococcal meningitis. One protocol was designed as a nested PCR to be performed in conventional block thermal cyclers. The other protocol was designed as a quantitative single-round PCR adapted to LightCycler technology. One hundred brain homogenates and dilutions originating from 20 ICR mice treated with different azoles were examined. A fungal burden of 3 x 10(1) to 2.9 x 10(4) CFU per mg of brain tissue was determined by quantitative culture. Specific PCR products were amplified by the conventional and the LightCycler methods in 86 and 87 samples, respectively, with products identified by DNA sequencing and real-time fluorescence detection. An analytical sensitivity of 1 CFU of C. neoformans per mg of brain tissue and less than 10 CFU per volume used for extraction was observed for both PCR protocols, while homogenates of 70 organs from mice infected with other fungi were PCR negative. Specificity testing was performed with genomic DNA from 31 hymenomycetous fungal species and from the ustilaginomycetous yeast Malassezia furfur, which are phylogenetically related to C. neoformans. Twenty-four strains, including species of human skin flora like M. furfur and Trichosporon spp., were PCR negative. Amplification was observed with Cryptococcus amylolentus, Filobasidiella depauperata, Cryptococcus laurentii, and five species unrelated to clinical specimens. LightCycler PCR products from F. depauperata and Trichosporon faecale could be clearly discriminated by melting curve analysis. The sensitive and specific nested PCR assay as well as the rapid and quantitative LightCycler PCR assay might be useful for the diagnosis and monitoring of human cryptococcal infections.