Blood-based host biomarker diagnostics in active case finding for pulmonary tuberculosis: A diagnostic case-control study

Abstract

Background There is a need to identify scalable tuberculosis screening strategies among high burden populations. The WHO has identified a non-sputum-based triage test as a development priority. Methods We performed a diagnostic case-control study of point-of-care C-reactive protein (CRP) and Prototype-Xpert-MTB-Host-Response (Xpert-MTB-HR) assays in the context of a mass screening program for tuberculosis in two prisons in Brazil. All incarcerated individuals irrespective of symptoms were screened by sputum Xpert MTB/RIF and sputum culture. Among consecutive, Xpert MTB/RIF or culture-confirmed cases and Xpert MTB/RIF and culture-negative controls, CRP was quantified in serum by a point-of-care assay (iChroma-II) and a 3-gene expression score was quantified from whole blood using the Xpert-MTB-HR cartridge. We evaluated receiver operating characteristic area under the curve (AUC) and assessed specificity at 90% sensitivity and sensitivity at 70% specificity, consistent with WHO target product profile (TPP) benchmarks. Findings Two hundred controls (no TB) and 100 culture- or Xpert MTB/RIF-positive tuberculosis cases were included. Half of tuberculosis cases and 11% of controls reported any tuberculosis symptoms. AUC for CRP was 0·79 (95% CI: 0·73–0·84) and for Xpert-MTB-HR was 0·84 (95% CI: 0·79–0·89). At 90% sensitivity, Xpert-MTB-HR had significantly higher specificity (53·0%, 95% CI: 45·0–69·0%) than CRP (28·1%, 95% CI: 20·2–41·8%) ( p = 0·003), both well below the TPP benchmark of 70%. Among individuals with medium or high sputum Xpert MTB/RIF semi-quantitative load, sensitivity (at 70% specificity) of CRP (90·3%, 95% CI: 74·2–98·0) and Xpert-MTB-HR (96·8%, 95% CI: 83·3–99·9%) was higher. Interpretation For active case finding in this high tuberculosis-burden setting, CRP and Xpert-MTB-HR did not meet TPP benchmarks for a triage test. However, Xpert-MTB-HR was highly sensitive in detecting individuals with medium or high sputum bacillary burden. Funding National Institutes of Health (R01 AI130058 and R01 AI149620) and Brazilian National Council for Scientific and Technological Development (CNPq-404182/2019-4).

Mycobacterium tuberculosis infection, immune activation, and risk of HIV acquisition

“…The Sweeney3 signature was most strongly associated with HIV risk in unadjusted and adjusted analyses, and in the LTBI-negative, but not the LTBI-positive group. This three-gene set predicts the presence of active TB disease versus LTBI with better accuracy (86% sensitivity, 86% specificity) than most combinations of clinical prediction tools, and with similar sensitivity to GeneXpert-MTB RIF sputum tests [ 42 , 43 ]. Because the three genes, GBP5, DUSP3, and KLF2, are associated with macrophage regulation and other immune pathways [ 44 – 46 ], this gene set may detect a high-risk systemic immune status, provoked by genital or gastrointestinal infection or altered microbiome composition, which could also be differentially associated with LTBI status.…”

Reimagining the status quo: How close are we to rapid sputum-free tuberculosis diagnostics for all?

“… Triage Collection method and not a test itself - Studies are few and heterogenous, no pooled performance estimates exist - Ultra applied to a single swab had a sensitivity of 88% in outpatients 41 but only 43% sensitivity when used for active case finding in a prison 40 - TB-LAMP 42 applied to oral swabs had sensitivities ranging from 33-50% - FLOQSwabs (Copan Italia) preferred 41 - Self-swabbing, comparable to health worker-administered swabs for other pathogens 44 , appears feasible - Potential for paediatric TB 43 - Insufficient Mtb may be recovered from swabs in patients with low sputum bacillary load 40 - Performance of novel assays (e.g., next-generation LAM and NAATs unknown) may overcome sensitivity limitations associated - Optimal number of swabs, swab design, and the processing method are under evaluation and may improve the release of material from swabs -No tests purpose-built for tongue swabs yet exist Blood Host transcriptome mRNA blood signatures associated with the immune system's response to Mtb have shown promise for diagnosis. 68 Triage Xpert Host Response (Cepheid) - A multicentre study showed 90% sensitivity and 86% specificity 64 -Other studies have shown lower specificities (26% 101 , 53% 102 ) at >90% sensitivity - Limited data with small numbers of cases, however, multicentre studies are emerging - Xpert HR has the most data available - RNA is labile and, for Xpert HR, time from blood collection to testing must be <30 min and stabilisation agents may be required - Cost unclear, but likely high - Potential utility treatment response monitoring, management of diseases other than TB (signature-positive patients without TB could have other infections 95 ), and false-positive TB PCR results 65 , which are frequent in people with previous TB 68 , 84 , 103 - Signatures (including Sweeney3 in Xpert HR) measured using ultra-sensitive methods (sequencing, Nanostring) 68 struggle to meet WHO TPPs 65 , 66 ...…”

Mycobacterium tuberculosisinfection, immune activation, and risk of HIV acquisition

“…This three-gene set predicts the presence of active TB disease versus LTBI with better accuracy (86% sensitivity, 86% specificity) than most combinations of clinical prediction tools, and with similar sensitivity to GeneXpert-MTB RIF sputum tests. [43,44] Because the three genes, GBP5, DUSP3, and KLF2, are associated with immune signaling pathways and macrophage regulation [45][46][47], this gene set may detect a high-risk systemic immune status related to genital or gastrointestinal infection or altered microbiome composition, which could also be differentially associated with LTBI status. In contrast, the RESPONSE5 profile evaluates differential gene expression that predicts cure after TB treatment, wherein a high score represents higher innate immune activation [28], and higher scores were associated with lower odds of HIV acquisition in this cohort.…”