Rapid diagnosis of cryptococcosis using an antigen detection immunochromatographic test

Laboratory validation of targeted next-generation sequencing assay for pathogen detection in lower respiratory infection

Lower respiratory tract infection (LRTI) is a serious global public health issue and poses significant challenges for detection and diagnosis. We validated the detection performance of targeted next-generation sequencing (tNGS) based on multiplex PCR using simulated microbial sample panels and clinical samples, providing a theoretical basis for promoting and applying tNGS in clinical diagnosis. We used a series of simulated microbial sample panels to validate the analytical validity of tNGS comprehensively. We also use tNGS to test respiratory specimens from 108 diagnosed or suspected LRTI patients to validate its clinical validity in diagnosing LRTI. Finally, we summarize the drug-resistance genes obtained from tNGS, the detection cost, and the turnaround time. tNGS has good analytical specificity, sensitivity, and precision. It has good stability when stored under low-temperature conditions. Using the composite diagnostic criteria as the gold standard, our internal tNGS platform has a sensitivity of 84.38%, specificity of 91.67%, positive predictive value of 98.78%, and negative predictive value of 42.31%. In terms of turnaround time, tNGS (about 16 h) and metagenomic next-generation sequencing (about 24 h) are similar, both significantly superior to traditional microbial detection methods (3-5 days). The cost of tNGS is approximately one-fourth of metagenomic next-generation sequencing. As a novel method with acceptable performance and cost, tNGS can compensate for the shortcomings of commonly used pathogen detection schemes in clinical practice, and its application prospects are worth looking forward to.

IMPORTANCE

Lower respiratory tract infection (LRTI) is a serious global public health problem, and detecting its pathogenic microorganisms is difficult. Targeted next-generation sequencing (tNGS) is a rising star in microbial detection, with enormous potential. To understand the detection performance of tNGS and provide a theoretical basis for promoting its application in clinical diagnosis, this study prepared simulated microbial sample panels using reference materials to evaluate the analytical and clinical validity of tNGS. Our research suggests that tNGS has good analytical specificity and sensitivity, precision, and stability. Additionally, it can reliably detect common LRTI pathogens. It has advantages in identifying co-infections and atypical pathogens. Moreover, tNGS significantly reduces turnaround time, allowing faster treatment. In summary, tNGS is expected to be used in clinical practice to diagnose and manage LRTI.

Comparing the Performance of Two Cryptococcal Antigen Detection Tests: Chemiluminescence vs Colloidal Gold Methods

Objective

To compare the performance of a new chemiluminescence method with that of the traditional colloidal gold method for cryptococcal antigen (CrAg) detection.

Methods

Cryptococcosis is a global invasive mycosis associated with significant morbidity and mortality. Cryptococcal antigen (CrAg) testing from serum and cerebrospinal fluid (CSF) has been regarded as the gold standard for early diagnosis. In this study, a total of 140 samples (92 serum and 48 cerebrospinal fluid samples) from 140 patients with suspected cryptococcosis collected between January 2022 and September 2023 at Zhejiang Provincial People's Hospital were tested via a fully automated chemiluminescent immunoassay analyser (SuperFlex) from Suzhou Xinbo and a cryptococcal antigen detection kit (colloidal gold method) from the IMMY Company of the United States.

Results

According to the diagnostic criteria for cryptococcosis, 55 of the 140 suspected patients were diagnosed with cryptococcosis (39.3%), including 47 with pulmonary cryptococcosis (PC) and 8 with cryptococcal meningitis (CM). The degree of agreement between chemiluminescence and the colloidal gold method was analysed via Cohen's kappa coefficient, which was 0.970 (P<0.01). The sensitivities of the chemiluminescence and colloidal gold methods were 98.2% and 96.4%, respectively, and their specificities were 100% and 98.8%, respectively. The area under the receiver operating characteristic (ROC) curve were 0.996 for chemiluminescence and 0.9759 for the colloidal gold method. The area under the curve (AUC) of the two methods did not differ significantly (P=0.086).

Conclusion

For the detection of CrAg, the new chemiluminescence method is highly consistent with the traditional colloidal gold method and has higher sensitivity and specificity for the diagnosis of cryptococcosis.

The significance of low titer serum cryptococcal antigen testing from 2017 to 2023 performed in a tertiary care center

Several false positive low serum cryptococcal antigen (SCrAg) reports by lateral flow assay (LFA) were identified in late 2016 at our tertiary care hospital. After the recall and correction of the problem in the reagent, we studied the significance of SCrAg LFA ≤ 1:10 from January 2017 to October 2023. Of 20 patients with 31 samples of SCrAg LFA ≤ 1:10, 14 patients (70%) were classified as true positives, four (20%) were indeterminate, and only two (10%) patients were false positives. If a new SCrAg LFA ≤ 1:10 is detected, it should be repeated, and additional workup should be pursued.

Prevalence of Cryptococcal Antigenemia and Lateral Flow Assay Accuracy in Severely Immunosuppressed AIDS Patients

This study aimed to estimate the prevalence of cryptococcal antigenemia detected by lateral flow assay (LFA) in AIDS patients and its accuracy in the diagnosis of cryptococcosis. Conducted at a university hospital in Brazil from March 2015 to July 2017, it included AIDS patients over 18 years old with a CD4+ count ≤ 200 cells/mm3. Cryptococcal antigen (CrAg) detection using LFA and latex agglutination (LA), along with blood and urine cultures, were performed. The reference standard was the identification of Cryptococcus spp. in clinical specimens through microbiological or histopathological examination. Among 230 patients, the prevalence of CrAg detected by LFA (CrAg LFA) was 13.0%. Factors associated with cryptococcal antigenemia included fever, vomiting, seizures, and a lack of antiretroviral therapy. The sensitivity and specificity of CrAg LFA were 83.9% and 98.0%, respectively. The positive predictive value (PPV) was 86.7%, the negative predictive value (NPV) was 97.5%, and overall accuracy was 96.1%. Cross-reactions were observed in patients with histoplasmosis and paracoccidioidmycosis, but not with aspergillosis or positive rheumatoid factor. The study concludes that the LFA is a useful tool for detecting cryptococcal antigenemia in severely immunocompromised AIDS patients due to its high NPV, specificity, and PPV.

Clinical utility of cryptococcal antigen detection in transthoracic needle aspirate by lateral flow assay for diagnosing non-HIV pulmonary cryptococcosis: A multicenter retrospective study

Lateral flow immunoassay (LFA) detection of cryptococcal capsular polysaccharide antigen (CrAg) is reported to be the most rapid and convenient laboratory method for diagnosing cryptococcosis. Its clinical diagnostic use, however, is not well studied. We retrospectively analyzed the data from 97 patients with suspected pulmonary cryptococcosis (PC) at 2 tertiary care centers. CrAg in both serum and lung aspirate specimens were examined by LFA. We divided the patients who were diagnosed with PC into group I, patients positive for CrAg in both the serum and lung aspirate, and group II, patients positive for CrAg in the lung aspirate but not in the serum. We analyzed the differences in imaging distribution, morphological characteristics, and concomitant signs between the 2 groups. Of all 97 patients, 47 were diagnosed with PC. Lung aspirates were positive for CrAg in 46/47 patients with PC (sensitivity 97.9%, specificity 100%, positive predictive value = 100%, negative predictive value = 98%). There were no false positive results in the noncryptococcosis patients, revealing a diagnostic accuracy of 99%. Serum CrAg tests were positive in 36/47 patients with PC (sensitivity 76.6%, specificity 100%, accuracy 88.7%, positive predictive value = 100%, negative predictive value = 82%). Chest imaging data showed a statistically significant greater number of single lesions in group II than in group I (P < .05). More lesions accompanied by halo signs were showed in group I (P < .01), whereas more accompanied by pleural stretch signs were found in group II (P < .01). The LFA-positive rate of CrAg in lung aspirate samples was higher than that of the serum samples, especially in patients with single pulmonary lesion or in those accompanied by pleural stretch. The direct measurement of CrAg in lung aspirate is a rapid, useful alternative diagnostic method for PC confirmation.

Consensus guidelines for the diagnosis and management of cryptococcosis and rare yeast infections in the haematology/oncology setting, 2021

Cryptococcosis caused by the Cryptococcus neoformans-Cryptococcus gattii complex is an important opportunistic infection in people with immunodeficiency, including in the haematology/oncology setting. This may manifest clinically as cryptococcal meningitis or pulmonary cryptococcosis, or be detected incidentally by cryptococcal antigenemia, a positive sputum culture or radiological imaging. Non-Candida, non-Cryptococcus spp. rare yeast fungaemia are increasingly common in this population. These consensus guidelines aim to provide clinicians working in the Australian and New Zealand haematology/oncology setting with clear guiding principles and practical recommendations for the management of cryptococcosis, while also highlighting important and emerging rare yeast infections and their recommended management.

A Novel, Inexpensive In-House Immunochromatographic Strip Test for Cryptococcosis Based on the Cryptococcal Glucuronoxylomannan Specific Monoclonal Antibody 18B7

The aim of this study was to develop a novel lateral flow immunochromatoghaphic strip test (ICT) for detecting cryptococcal polysaccharide capsular antigens using only a single specific monoclonal antibody, mAb 18B7. The mAb 18B7 is a well characterized antibody that specifically binds repeating epitopes displayed on the cryptococcal polysaccharide glucuronoxylomannan (GXM). We validated the immunoreactivities of mAb 18B7 against capsular antigens of different cryptococcal serotypes. The mAb 18B7 ICT was constructed as a sandwich ICT strip and the antibody serving in the mobile phase (colloidal gold conjugated mAb 18B7) to bind one of the GXM epitopes while the stationary phase antibody (immobilized mAb18B7 on test line) binding to other remaining unoccupied epitopes to generate a positive visual readout. The lower limit of detection of capsular antigens for each of the Cryptococcus serotypes tested was 0.63 ng/mL. No cross-reaction was found against a panel of antigens isolated from cultures of other pathogenic fungal, except the crude antigen of Trichosporon sp. with the lower limit of detection of 500 ng/mL (~800 times higher than that for cryptococcal GXM). The performance of the mAb 18B7 ICT strip was studied using cerebrospinal fluid (CSF) and serum and compared to commercial diagnostic kits (latex agglutination CALAS and CrAg IMMY). The sensitivity, specificity and accuracy of the mAb18B7 ICT with CSF from patients with confirmed cryptococcal meningitis were 92.86%, 100% and 96.23%, respectively. No false positives were observed with samples from non-cryptococcosis patients. With serum samples, the mAb 18B7 ICT gave a sensitivity, specificity and accuracy of 96.15%, 97.78% and 96.91%, respectively. Our results show that the mAb 18B7 based ICT was reliable, reproducible, and cost-effective as a point-of-care immunodiagnostic test for cryptococcosis. The mAb 18B7 ICT may be particularly useful in countries where commercial kits are not available or affordable.

Evaluation of lateral flow immunochromatographic assay for diagnostic accuracy of cryptococcosis

Background

Cryptococcus is a conditional pathogenic fungus causing cryptococcosis, which is one of the most serious fungal diseases faced by humans. Lateral flow immunochromatographic assay (LFA) is successfully applied to the rapid detection of cryptococcal antigens.

Methods

Studies were retrieved systematically from the Embase, PubMed, Web of Science, and Cochrane Library before July 2019. The quality of the studies was assessed by Review Manager 5.0 based on the Quality Assessment of Diagnostic Accuracy Study guidelines. The extracted data from the included studies were analyzed by Meta-DiSc 1.4. Stata 12.0 software was used to detect the publication bias.

Results

A total of 15 articles with 31 fourfold tables were adopted by inclusion and exclusion criteria. The merged sensitivity and specificity in serum were 0.98 and 0.98, respectively, and those in the cerebrospinal fluid were 0.99 and 0.99, respectively.

Conclusions

Compared to the urine and other samples, LFA in serum and cerebrospinal fluid is favorable evidence for the diagnosis of cryptococcosis with high specificity and sensitivity.

Evaluation of low cryptococcal antigen titer as determined by the lateral flow assay in serum and cerebrospinal fluid among HIV-negative patients: a retrospective diagnostic accuracy study

Cryptococcosis is one of the most common opportunistic infections in both immunocompetent and immunocompromised hosts. Although the cryptococcal antigen (CrAg) lateral flow assay (LFA) has been widely used in clinical settings due to its high sensitivity and specificity, the diagnostic value of a low CrAg LFA titers remains unclear. In this study, we performed a retrospective analysis of 149 HIV-negative patients with low CrAg LFA titers (≤1:10) in a Chinese tertiary hospital from January 2013 to December 2017, to evaluate the diagnostic value of low CrAg LFA titers in serum and cerebrospinal fluid (CSF) at different thresholds. Sensitivity and specificity of low CrAg LFA titers in patients with definitive diagnoses of cryptococcosis were 39.6% (95% CI, 29.7–50.1%) and 100% (95% CI, 69.2–100%), respectively, at a threshold of 1:10 in serum. A sensitivity of 72.9% (95% CI, 62.9–81.5%) and a decreased specificity of 70.0% (95% CI, 34.8–93.3%) were observed at a threshold of 1:5 in serum. No false-positive cases were identified in patients with low CrAg titers in CSF and all positive predictive values (PPVs) were 100%. Among the cases with low serum CrAg titers, lumbar puncture was performed in 97 patients and positive CSF CrAg titers were reported in 6 patients. In conclusion, the results of this study imply that low CrAg LFA titer, either in serum or CSF, is crucial for early diagnosis of cryptococcosis in HIV-negative patients, and lumbar puncture is recommended to be performed routinely for CSF testing when a positive low serum titer is reported. Cryptococcal meningitis should be considered seriously when the CSF CrAg titer is positive.

Prevalence of cryptococcal antigenemia and nasal colonization in a free-ranging koala population

Cryptococcosis, caused by environmental fungi in the Cryptococcus neoformans and Cryptococcus gattii species complexes, affects a variety of hosts, including koalas (Phascolarctos cinereus). Cryptococcal antigenemia and nasal colonization are well characterized in captive koalas, but free-ranging populations have not been studied systematically. Free-ranging koalas (181) from the Liverpool Plains region of New South Wales, Australia, were tested for cryptococcal antigenemia (lateral flow immunoassay) and nasal colonization (bird seed agar culture). Results were related to environmental and individual koala characteristics. Eucalypt trees (14) were also randomly tested for the presence of Cryptococcus spp. by bird seed agar culture. In sum, 5.5% (10/181) and 6.6% (12/181) of koalas were positive for antigenemia and nasal colonization, respectively, on at least one occasion. And 64.3% (9/14) of eucalypts were culture-positive for Cryptococcus spp. URA5 restriction fragment length polymorphism analysis identified most isolates as C. gattii VGI, while C. neoformans VNI was only found in one koala and one tree. Colonized koalas were significantly more likely to test positive for antigenemia. No associations between antigenemia or colonization, and external environmental characteristics (the relative abundance of Eucalyptus camaldulensis and season), or individual koala characteristics (body condition, sex, and age), could be established, suggesting that antigenemia and colonization are random outcomes of host-pathogen-environment interactions. The relationship between positive antigenemia status and a relatively high abundance of E. camaldulensis requires further investigation. This study characterizes cryptococcosis in a free-ranging koala population, expands the ecological niche of the C. gattii/C. neoformans species complexes and highlights free-ranging koalas as important sentinels for this disease.

Evaluation of the clinical performance of 2 point-of-care cryptococcal antigen tests in dogs and cats

Background

Point‐of‐care (POC) Cryptococcus antigen assays may provide veterinarians with a more rapid, patient‐side diagnosis when compared with traditional laboratory‐based latex agglutination tests.

Objective

To determine the sensitivity and specificity of 2 POC lateral flow cryptococcal serum antigen tests, CrAg LFA (Immy, Norman, OK) and the CryptoPS (Biosynex, Strasbourg, France) for diagnosis of cryptococcosis in dogs and cats, using the cryptococcal antigen latex agglutination system (CALAS) as the reference standard.

Animals

102 serum samples from 51 dogs and 40 cats.

Methods

Specimens were classified as CALAS‐positive (n = 25) or CALAS‐negative (n = 77). The sensitivity and specificity of each POC assay was calculated by comparing the results to the serologic reference standard results.

Results

The CrAg LFA assay correctly classified 23/25 CALAS‐positive specimens and 69/74 CALAS‐negative specimens resulting in a sensitivity of 92.0% (confidence interval [CI], 75.0%‐98.6%) and specificity of 93.2% (CI, 85.1%‐97.1%). The CryptoPS assay correctly classified 8/10 tested CALAS‐positive specimens and 56/59 tested CALAS‐negative specimens resulting in a sensitivity of 80.0% (CI, 49.0%‐96.5%) and specificity of 94.9% (CI, 86.1%‐98.6%).

Conclusion and Clinical Importance

The POC assays appear to be a sensitive and specific alternative to the traditional CALAS assay with more rapid turnaround times, which may result in earlier diagnosis and treatment.

Low Cryptococcus Antigen Titers as Determined by Lateral Flow Assay Should Be Interpreted Cautiously in Patients without Prior Diagnosis of Cryptococcal Infection

Detection of Cryptococcus antigen (CrAg) is invaluable for establishing cryptococcal disease. Multiple different methods for CrAg detection are available, including a lateral flow assay (LFA). Despite excellent performance of the CrAg LFA, we have observed multiple cases of low-titer (≤1:5) positive CrAg LFA results in patients for whom cryptococcosis was ultimately excluded. To investigate the accuracy of low-titer positive CrAg LFA results, we performed chart reviews for all patients with positive CrAg LFA results between June 2014 and December 2016. During this period, serum and/or cerebrospinal fluid (CSF) samples from 3,969 patients were tested with the CrAg LFA, and 55 patients (1.5%) tested positive. Thirty-eight of those patients lacked a history of cryptococcal disease and were the focus of this study. Fungal culture or histopathology confirmed Cryptococcus infection for 20 patients (52.6%), and CrAg LFA titers in serum and CSF samples ranged from 1:5 to ≥1:2,560. For the 18 patients (47.4%) without culture or histopathological confirmation, the CrAg LFA results were considered true-positive results for 5 patients (titer range, 1:10 to ≥1:2,560), due to clinical improvement with targeted therapy and decreasing CrAg LFA titers. The remaining 13 patients had CrAg LFA titers of 1:2 (n = 11) or 1:5 (n = 2) and were ultimately diagnosed with an alternative condition (n = 11) or began therapy for possible cryptococcosis without improvement (n = 2), leading to an overall CrAg LFA false-positive rate of 34%. We recommend careful clinical correlation prior to establishing a diagnosis of cryptococcal infection for patients with first-time positive CrAg LFA titers of 1:2.

Cryptococcus tetragattii as a major cause of cryptococcal meningitis among HIV-infected individuals in Harare, Zimbabwe

OBJECTIVES

HIV-associated cryptococcal meningitis is commonly caused by Cryptococcus neoformans, whilst infections with Cryptococcus gattii sensu lato are historically rare. Despite available studies, little is known about the occurrence of C. gattii sensu lato infections among HIV-infected individuals in Zimbabwe.

METHODS

In a prospective cohort, we investigated the prevalence of C. gattii sensu lato meningitis among HIV-infected patients (n = 74) in Harare, Zimbabwe.

RESULTS

Of the 66/74 isolates confirmed by molecular characterization, 16.7% (11/66) were found to be C. gattii sensu lato and 83.3% (55/66) C. neoformans sensu stricto. From one patient two phenotypically different C. gattii sensu lato colonies were cultured. The majority (n = 9/12; 75%) of the C. gattii sensu lato isolates were Cryptococcus tetragattii (AFLP7/VGIV), which has been an infrequently reported pathogen. In-hospital mortality associated with C. gattii sensu lato was 36.4%.

CONCLUSIONS

Our data suggests that C. tetragattii (AFLP7/VGIV) is a more common cause of disease than C. gattii sensu stricto (genotype AFLP4/VGI) among patients with HIV-associated cryptococcal meningitis in Harare, Zimbabwe and possibly underreported in sub-Saharan Africa.

Use of Piezoelectric Immunosensors for Detection of Interferon-Gamma Interaction with Specific Antibodies in the Presence of Released-Active Forms of Antibodies to Interferon-Gamma

In preliminary ELISA studies where released-active forms (RAF) of antibodies (Abs) to interferon-gamma (IFNg) were added to the antigen-antibody system, a statistically significant difference in absorbance signals obtained in their presence in comparison to placebo was observed. A piezoelectric immunosensor assay was developed to support these data and investigate the effects of RAF Abs to IFNg on the specific interaction between Abs to IFNg and IFNg. The experimental conditions were designed and optimal electrode coating, detection circumstances and suitable chaotropic agents for electrode regeneration were selected. The developed technique was found to provide high repeatability, intermediate precision and specificity. The difference between the analytical signals of RAF Ab samples and those of the placebo was up to 50.8%, whereas the difference between non-specific controls and the placebo was within 5%–6%. Thus, the piezoelectric immunosensor as well as ELISA has the potential to be used for detecting the effects of RAF Abs to IFNg on the antigen-antibody interaction, which might be the result of RAF’s ability to modify the affinity of IFNg to specific/related Abs.

Performance of the Cryptococcal Antigen Lateral Flow Assay in Non-HIV-Related Cryptococcosis

The cryptococcal antigen lateral flow assay (CrAg LFA) was evaluated for the diagnosis of cryptococcosis in HIV-negative patients. The sensitivity was excellent, suggesting that this assay can replace conventional testing based on latex agglutination (LA). CrAg LFA and LA titers were correlated but were not directly comparable, with implications for conversion between assays.