Xpert MTB/RIF Ultra is highly sensitive for the diagnosis of tuberculosis lymphadenitis in an HIV-endemic setting

Blood RNA signatures outperform CRP triage of tuberculosis lymphadenitis and pericarditis

Background

Limited data are available on the diagnostic accuracy of blood RNA biomarker signatures for extrapulmonary TB (EPTB). We addressed this question among people investigated for TB lymphadenitis and TB pericarditis, in Cape Town, South Africa.

Methods

We enrolled 440 consecutive adults referred to a hospital for invasive sampling for presumptive TB lymphadenitis (n=300) or presumptive TB pericarditis (n=140). Samples from the site of disease underwent culture and/or molecular testing for Mycobacterium tuberculosis complex (Mtb). Discrimination of patients with and without TB defined by microbiology or cytology reference standards was evaluated using seven previously reported blood RNA signatures by area under the receiver-operating characteristic curve (AUROC) and sensitivity/specificity at predefined thresholds, benchmarked against blood C-reactive protein (CRP) and the World Health Organization (WHO) target product profile (TPP) for a TB triage test. Decision curve analysis (DCA) was used to evaluate the clinical utility of the best performing blood RNA signature and CRP.

Results

Data from 374 patients for whom results were available from at least one microbiological test from the site of disease, and blood CRP and RNA measurements, were included. Using microbiological results as the reference standard in the primary analysis (N=204 with TB), performance was similar across lymphadenitis and pericarditis patients. In the pooled analysis of both cohorts, all RNA signatures had comparable discrimination with AUROC point estimates ranging 0.77-0.82, superior to that of CRP (0.61, 95% confidence interval 0.56-0.67). The best performing signature (Roe3) achieved an AUROC of 0.82 (0.77-0.86). At a predefined threshold of 2 standard deviations (Z2) above the mean of a healthy reference control group, this signature achieved 78% (72-83%) sensitivity and 69% (62-75%) specificity. In this setting, DCA revealed that Roe3 offered greater net benefit than other approaches for services aiming to reduce the number needed to investigate with confirmatory testing to <4 to identify each case of TB.

Interpretation

RNA biomarkers show better accuracy and clinical utility than CRP to trigger confirmatory TB testing in patients with TB lymphadenitis and TB pericarditis, but still fall short of the WHO TPP for TB triage tests.

Funding

South African MRC, EDCTP2, NIH/NIAID, Wellcome Trust, NIHR, Royal College of Physicians London.

Research in context

Evidence before this study: Blood RNA biomarker signatures and CRP measurements have emerged as potential triage tests for TB, but evidence is mostly limited to their performance in pulmonary TB. Microbiological diagnosis of extrapulmonary TB (EPTB) is made challenging by the need for invasive sampling to obtain tissue from the site of disease. This is compounded by lower sensitivity of confirmatory molecular tests for EPTB compared to their performance in pulmonary disease. We performed a systematic review of diagnostic accuracy studies of blood RNA biomarkers or CRP measurements for EPTB, which could mitigate the need for site-of-disease sampling for the diagnosis of TB. We searched PubMed up to 1 st August 2023, using the following criteria: "extrapulmonary [title/abstract] AND tuberculosis [title/abstract] AND biomarker [title/abstract]". Although extrapulmonary TB was included in several studies, none focused specifically on EPTB or included an adequate number of EPTB cases to provide precise estimates of test accuracy. Added value of this study: To the best of our knowledge, we report the first diagnostic accuracy study of blood RNA biomarkers and CRP for TB among people with EPTB syndromes. We examined the performance of seven previously identified blood RNA biomarkers as triage tests for TB lymphadenitis and TB pericarditis compared to a microbiology reference standard among people referred to hospital for invasive sampling in a high TB and HIV prevalence setting. Multiple blood RNA biomarkers showed comparable diagnostic accuracy to that previously reported for pulmonary TB in both EPTB disease cohorts, irrespective of HIV status. All seven blood RNA biomarkers showed superior diagnostic accuracy to CRP for both lymphadenitis and pericarditis, but failed to meet the combined >90% sensitivity and >70% specificity recommended for a blood-based diagnostic triage test by WHO. Nonetheless, in decision curve analysis, an approach of using the best performing blood RNA biomarker to trigger confirmatory microbiological testing showed superior clinical utility in clinical services seeking to reduce the number needed to test (using invasive confirmatory testing) to less than 4 for each EPTB case detected. If acceptable to undertake invasive testing in more than 4 people for each true case detected, then a test-all approach will provide greater net benefit in this TB/HIV hyperendemic setting.Implications of all the available evidence: Blood RNA biomarkers show some potential as diagnostic triage tests for TB lymphadenitis and TB pericarditis, but do not provide the level of accuracy for blood-based triage tests recommended by WHO for community-based tests. CRP has inferior diagnostic accuracy to blood RNA biomarkers and cannot be recommended for diagnostic triage among people with EPTB syndromes referred for invasive sampling.

A Retrospective Analysis of the Clinicopathological Features of Patients with Tuberculous Mastitis: A Single Institution's Experience

INTRODUCTION

Tuberculosis remains a global health burden, especially in low- and middle-income countries. Breast tuberculosis is a rare disease with minimal research available. This disease produces a diagnostic challenge as the clinical presentation is variable, and diagnosis often requires additional investigations. This study was undertaken to determine the efficacy of cytology and histology, together with ancillary studies, in diagnosing tuberculous mastitis.

METHODS

This retrospective study was conducted in a Johannesburg Hospital over 5 years. Thirty-two patients with confirmed tuberculous mastitis were included. The patients were considered positive for tuberculous mastitis if histological or cytological findings were confirmed with either a positive tuberculosis culture, Ziehl-Neelsen stain, or polymerase chain reaction examination/GeneXpert.

RESULTS

This case series comprises 3 males and 29 females with a mean age of 35.66. A breast mass was the most common presentation. Over these 5 years, more biopsies were performed on inflammatory breast lesions than fine needle aspirations. There was a higher confirmation rate for cytology diagnoses compared to histology diagnoses.

CONCLUSION

This study supports using fine needle aspiration combined with GeneXpert as the primary diagnostic modality in diagnosing tuberculous mastitis. This test combination is advantageous in resource- and financially constrained environments as it is relatively simple to perform, cost-effective, and has a rapid turnaround time.

Diagnosis of extrapulmonary tuberculosis by GeneXpert MTB/RIF Ultra assay

INTRODUCTION

Diagnosis of extrapulmonary tuberculosis (EPTB) is an arduous task owing to different anatomical locations, unusual clinical presentations, and sparse bacillary load in clinical specimens. Although GeneXpert® MTB/RIF is a windfall in TB diagnostics including EPTB, it yields low sensitivities but high specificities in many EPTB specimens. To further improve the sensitivity of GeneXpert®, GeneXpert® Ultra, a fully nested real-time PCR targeting IS6110, IS1081 and rpoB (Rv0664) has been endorsed by the WHO (2017), wherein melt curve analysis is utilized to detect rifampicin-resistance (RIF-R).

AREA COVERED

We described the assay chemistry/work design of Xpert Ultra and evaluated its performance in several EPTB types, that is, TB lymphadenitis, TB pleuritis, TB meningitis, and so on, against the microbiological reference standard or composite reference standard. Notably, Xpert Ultra exhibited better sensitivities than Xpert, but mostly at the compensation of specificity values. Moreover, Xpert Ultra exhibited low false-negative and false-positive RIF-R results, compared with Xpert. We also detailed other molecular tests, that is, Truenat MTBTM/TruPlus, commercial real-time PCR, line probe assay, and so on, for EPTB diagnosis.

EXPERT OPINION

A combination of clinical features, imaging, histopathological findings, and Xpert Ultra are adequate for definite EPTB diagnosis so as to initiate an early anti-tubercular therapy.

More than Mycobacterium tuberculosis: site-of-disease microbial communities, and their functional and clinical profiles in tuberculous lymphadenitis

BACKGROUND

Lymphadenitis is the most common extrapulmonary tuberculosis (EPTB) manifestation. The microbiome is important to human health but uninvestigated in EPTB. We profiled the site-of-disease lymph node microbiome in tuberculosis lymphadenitis (TBL).

METHODS

Fine-needle aspiration biopsies were collected from 158 pretreatment presumptive TBL patients in Cape Town, South Africa. 16S Illumina MiSeq rRNA gene sequencing was done.

RESULTS

We analysed 89 definite TBLs (dTBLs) and 61 non-TBLs (nTBLs), which had similar α- but different β-diversities (p=0.001). Clustering identified five lymphotypes prior to TB status stratification: Mycobacterium-dominant, Prevotella-dominant and Streptococcus-dominant lymphotypes were more frequent in dTBLs whereas a Corynebacterium-dominant lymphotype and a fifth lymphotype (no dominant taxon) were more frequent in nTBLs. When restricted to dTBLs, clustering identified a Mycobacterium-dominant lymphotype with low α-diversity and non-Mycobacterium-dominated lymphotypes (termed Prevotella-Corynebacterium, Prevotella-Streptococcus). The Mycobacterium dTBL lymphotype was associated with HIV-positivity and features characteristic of severe lymphadenitis (eg, larger nodes). dTBL microbial communities were enriched with potentially proinflammatory microbial short-chain fatty acid metabolic pathways (propanoate, butanoate) vs nTBLs. 11% (7/61) of nTBLs had Mycobacterium reads BLAST-confirmed as Mycobacterium tuberculosis complex.

CONCLUSIONS

TBL at the site-of-disease is not microbially homogeneous. Distinct microbial community clusters exist that, in our setting, are associated with different clinical characteristics, and immunomodulatory potentials. Non-Mycobacterium-dominated dTBL lymphotypes, which contain taxa potentially targeted by TB treatment, were associated with milder, potentially earlier stage disease. These investigations lay foundations for studying the microbiome's role in lymphatic TB. The long-term clinical significance of these lymphotypes requires prospective validation.

Epidemiology of extrapulmonary tuberculosis in central Guangxi from 2016 to 2021

The burden of extrapulmonary tuberculosis (EPTB) has gradually increased in recent years, but not enough epidemiological data is available from central Guangxi. To better understand the epidemiology of EPTB in central Guangxi and identify risk factors associated with them, we retrospectively investigated the epidemiology of tuberculosis (TB), especially EPTB, among patients admitted to the Chest Hospital of Guangxi Zhuang Autonomous Region between 2016 and 2021. We excluded those infected with both pulmonary tuberculosis (PTB) and EPTB, reported the proportion and incidence of PTB or EPTB, and compared the demographic characteristics and risk factors of EPTB and PTB cases using univariate and multivariate logistic regression models. Among 30,893 TB patients, 67.25% (20,774) had PTB and 32.75% (10,119) had EPTB. Among EPTB, pleural, skeletal, lymphatic, pericardial, meningeal, genitourinary, intestinal, and peritoneal TB accounted for 49.44%, 27.20%, 8.55%, 4.39%, 3.36%, 1.48%, 0.87%, and 0.79%, respectively. Patients who were younger (age < 25), from rural areas, Zhuang and other ethnic groups, and diagnosed with anemia and HIV infection were more likely to develop EPTB. However, patients with diabetes and COPD were less likely to have EPTB. From 2016 to 2021, the proportion of PTB cases decreased from 69.73 to 64.07%. The percentage of EPTB cases increased from 30.27 to 35.93%, with the largest increase in skeletal TB from 21.48 to 34.13%. The epidemiology and risk factors of EPTB in central Guangxi are different from those of PTB. The incidence of EPTB is increasing and further studies are needed to determine the reasons for it.

Xpert MTB/RIF Ultra in the auxiliary diagnosis of tuberculosis among people living with human immunodeficiency virus

Clinical diagnosis of tuberculosis (TB) in people living with the human immunodeficiency virus (HIV) poses a challenge. The Xpert MTB/RIF Ultra (Ultra) has displayed greater sensitivity at diagnosing tuberculosis and rifampicin resistance compared to the Xpert MTB/RIF (Xpert). However, whether Ultra is able to facilitate an auxiliary diagnosis of TB in patients with an HIV-TB co-infection remains unclear. Accordingly, the current study evaluated the use of Ultra in patients with an HIV-TB co-infection by summarizing relevant studies. The sensitivity and specificity of Ultra and Xpert at diagnosing patients with an HIV-TB co-infection have been summarized and compared. The performance of Ultra in diagnosing extrapulmonary tuberculosis was also summarized. Although a large-cohort, multi-center study needs to be conducted to assess Ultra's ability to detect TB in AIDS patients in the future, the current evidence supports the use of Ultra for the assessment of patients with an HIV-TB co-infection.

Xpert MTB/RIF Ultra outperformed the Xpert assay in tuberculosis lymphadenitis diagnosis: a prospective head-to-head cohort study

OBJECTIVES

Xpert MTB/RIF Ultra (Xpert-Ultra) has shown better sensitivity in comparison with Xpert MTB/RIF (Xpert) in extra-pulmonary tuberculosis, while the head-to-head comparison of these methods in tuberculosis lymphadenitis had barely been performed.

METHODS

Patients with undiagnosed lymphadenopathy were recruited prospectively and consecutively, and fine-needle aspirates biopsy (FNA) or lymph node tissue was collected. The specimen was subjected to smear, culture, Xpert and Xpert-Ultra assays. Culture and/or smear for AFB or AFB observed on histopathology were performed as a reference.

RESULTS

106 participants were recruited, including 41 confirmed TB, 33 probableTB and 32 non-TB lymphadenopathy. The head-to-head comparison for Mtb detection showed that Xpert-Ultra produced the highest sensitivity when compared with smear, culture and Xpert (75.7% vs. 5.4 %, 13.5% and 48.7%).When Xpert-Ultra outcomes were integrated for diagnosis, the percentage of confirmed TB lymphadenitis case increased from 55.4% (41/74) to 85.1% (63/74). The sensitivities of Xpert-Ultra and Xpert on tissue were 73.6% (95%CI,59.4-84.3) and 39.6% (95%CI,26.8-54.0), respectively. The sensitiviyt of Xpert-Ultra on FNA samples (81.0%,95%CI 57.4-93.7) was higher than that of Xpert (71.4%,95% CI 47.7-87.8).

CONCLUSIONS

Xpert-Ultra detected significantly more TB lymphadenitis cases than Xpert or culture. This superiority was particularly distinct using lymph node tissue than FNA detection.

Diagnosing Tuberculosis: What Do New Technologies Allow Us to (Not) Do?

New tuberculosis (TB) diagnostics are at a crossroads: their development, evaluation, and implementation is severely damaged by resource diversion due to COVID-19. Yet several technologies, especially those with potential for non-invasive non-sputum-based testing, hold promise for efficiently triaging and rapidly confirming TB near point-of-care. Such tests are, however, progressing through the pipeline slowly and will take years to reach patients and health workers. Compellingly, such tests will create new opportunities for difficult-to-diagnose populations, including primary care attendees (all-comers in high burden settings irrespective of reason for presentation) and community members (with early stage disease or risk factors like HIV), many of whom cannot easily produce sputum. Critically, all upcoming technologies have limitations that implementers and health workers need to be cognizant of to ensure optimal deployment without undermining confidence in a technology that still offers improvements over the status quo. In this state-of-the-art review, we critically appraise such technologies for active pulmonary TB diagnosis. We highlight strengths, limitations, outstanding research questions, and how current and future tests could be used in the presence of these limitations and uncertainties. Among triage tests, CRP (for which commercial near point-of-care devices exist) and computer-aided detection software with digital chest X-ray hold promise, together with late-stage blood-based assays that detect host and/or microbial biomarkers; however, aside from a handful of prototypes, the latter category has a shortage of promising late-stage alternatives. Furthermore, positive results from new triage tests may have utility in people without TB; however, their utility for informing diagnostic pathways for other diseases is under-researched (most sick people tested for TB do not have TB). For confirmatory tests, few true point-of-care options will be available soon; however, combining novel approaches like tongue swabs with established tests like Ultra have short-term promise but first require optimizations to specimen collection and processing procedures. Concerningly, no technologies yet have compelling evidence of meeting the World Health Organization optimal target product profile performance criteria, especially for important operational criteria crucial for field deployment. This is alarming as the target product profile criteria are themselves almost a decade old and require urgent revision, especially to cater for technologies made prominent by the COVID-19 diagnostic response (e.g., at-home testing and connectivity solutions). Throughout the review, we underscore the importance of how target populations and settings affect test performance and how the criteria by which these tests should be judged vary by use case, including in active case finding. Lastly, we advocate for health workers and researchers to themselves be vocal proponents of the uptake of both new tests and those - already available tests that remain suboptimally utilized.

Rapid Molecular Diagnosis of Extra-Pulmonary Tuberculosis by Xpert/RIF Ultra

Rapid detection of Mycobacterium tuberculosis complex and determination of drug resistance are essential for early diagnosis and treatment of tuberculosis (TB). Xpert MTB/RIF Ultra (Xpert Ultra), a molecular test that can simultaneously identify M. tuberculosis complex and resistance to rifampicin directly on clinical samples, is currently used. Xpert Ultra represents a helpful tool for rapid pulmonary TB diagnosis, especially in patients with paucibacillary infection. The aim of this review is to provide an overview of the diagnostic performance of Xpert Ultra in detection of extra-pulmonary tuberculosis.