Mark Hatherill

Background: Diagnostic performance of tongue swab Mycobacterium tuberculosis polymerase chain reaction (PCR) has been evaluated for triage of symptomatic tuberculosis (TB). It is unknown whether performance differs for detection of asymptomatic TB in community-based screening. Methods: Tongue swabs were collected from adult household contacts of persons with TB (HHC cohort), and symptomatic adults presenting with presumptive TB (clinic cohort), at six South African sites. Drug-susceptible pulmonary TB was defined by positive sputum Xpert Ultra (excluding trace) or liquid culture, which were performed in all participants. Tongue swabs from participants with and without TB, matched by propensity score, were tested by high-volume quantitative PCR (qPCR) and, in the clinic cohort, also by sequence-specific magnetic capture (SSMaC) with qPCR. Results: The clinic cohort included 217 participants with TB (100% symptomatic) and 437 participants without TB. The HHC cohort included 44 participants with TB (84.1% asymptomatic) and 136 participants without TB. In the clinic cohort, sensitivity of SSMaC with qPCR was 73.2% (specificity 94.6%), but not significantly higher than high-volume qPCR (63.8%; P = .14) (specificity 94.4%). Sensitivity of high-volume qPCR in the clinic cohort (63.8%) was significantly higher than the HHC cohort (34.1%; P = .0007) (specificity 91.9%). Among HHC, high-volume qPCR sensitivity was 35.1% for asymptomatic TB, 52.2% for TB with abnormal chest radiograph, and 100% for TB with high sputum Xpert Ultra grade. Conclusions: Sensitivity of tongue swab high-volume qPCR in community-based, household screening for asymptomatic TB was low, approximately half that of facility-based triage for symptomatic TB, but increased with radiographic severity and sputum bacillary load.

Background Antigen-specific CD4 T cells are essential but not sufficient for controlling Mycobacterium tuberculosis ( Mtb ) infection. We characterized changes in Mtb- specific CD4, and CD8 and γδ T cell frequencies and phenotypes during tuberculosis progression. Methods Mtb-infected adolescents, who remained healthy or progressed to tuberculosis, were followed longitudinally. Bulk and Mtb- specific T cells were profiled by intracellular cytokine staining and mass cytometry. Systemic inflammation was profiled by blood transcriptomics and proteomics. Features associated with disease progression or systemic inflammation were identified by mixed-effects modelling. Results Among many phenotypes of bulk CD4, CD8 and γδ T cells, only CD4 T cell activation (HLA-DR+) increased significantly during progression. However, levels of systemic inflammatory biomarkers of tuberculosis were strongly associated with changes in many phenotypic subsets of CD4, CD8 and γδ T cells. Similarly, among hundreds of Mtb- specific functional and phenotypic CD4 and CD8 T cell subsets, only two early-differentiated CD4 subsets (IL-2 ⁺ TNF ⁺ CD7 ⁺ CD27 ⁺ and IFNγ ⁺ IL-2 ⁺ TNF ⁺ CD7 ⁺ CD27 ⁺ ) significantly decreased, while Mtb -specific CD4 T cell activation increased during progression. These changes correlated with systemic inflammation. Conclusion Our findings suggest that peripheral blood frequencies and functions of Mtb-specific T cell subsets do not associate with tuberculosis progression, but that inflammation drives marked changes in T cell activation and differentiation.

Background: The efficacy and safety of the M72/AS01E tuberculosis (TB) candidate vaccine were evaluated in the phase 2b randomized, placebo-controlled trial NCT01755598. In the trial, participants with Mycobacterium tuberculosis sensitization by a positive interferon-gamma release assay received either M72/AS01E or placebo (randomized 1:1) and were followed for 3 years. In this descriptive study, we genetically characterized M. tuberculosis isolates from participants who developed pulmonary TB during the trial to assess variability among isolates and evaluate the possibility of preferential progression from infection to active TB by certain strains in M72/AS01E and placebo recipients. Methods: M. tuberculosis isolates were recovered from sputum samples and underwent DNA extraction and sequencing to assess lineage, antibiotic resistance profile, genetic variation, and genomic clusters. Results: One hundred isolates (37 M72/AS01E, 63 placebo) were genetically characterized from 50 participants who developed microbiologically confirmed active pulmonary TB during the trial (20 M72/AS01E, 30 placebo). Diverse M. tuberculosis lineages were identified in both M72/AS01E and placebo recipients. No multidrug-resistant strains were detected. Genetic sequences corresponding to the antigenic components of M72/AS01E showed low variation in pepA and high variation in PPE18. However, no apparent preferential distribution of variants was observed in M72/AS01E or placebo recipients. Cluster analyses identified 10 genomic clusters with isolates from >1 participant, illustrating complex transmission dynamics and potential of coinfection by multiple strains within individuals. Conclusions: This descriptive analysis showed no apparent preferential distribution of local M. tuberculosis strains in M72/AS01E or placebo recipients. These results support the continued development of this candidate vaccine. Clinical Trials Registration: The NCT01755598 study was registered at https://Cinicaltrials.gov on 19 December 2012. The trial protocol and statistical analysis plan can be accessed from the trial registration website https://clinicaltrials.gov/study/NCT01755598.

The WHO has recommended tongue swabs (TS) as alternative samples for microbiological diagnosis of tuberculosis. We evaluated the effects of oral hygiene and food/drink intake on TS performance in South Africa. Food/drink intake prior to sampling marginally decreased Mycobacterium tuberculosis DNA signal strength, but neither behaviour decreased diagnostic sensitivity.

A large proportion of individuals with tuberculosis (TB) are asymptomatic. The biological and inflammatory underpinnings of asymptomatic TB are unknown and may differ from symptomatic TB. We characterise blood transcriptomic and proteomic profiles in South African community screening vs. health facility-based triage cohorts. Asymptomatic TB shares core transcriptomic and proteomic features with symptomatic TB, including upregulation of innate, interferon and inflammatory pathways and downregulation of T and B cell pathways. Integration of transcriptomic and proteomic data from asymptomatic TB individuals identifies two distinct sub-clusters characterized by higher or lower bacterial burden, blood IFN-γ responses, BMI, and chest radiographic abnormalities, suggesting different disease severity. We identify a new blood transcriptomic signature of asymptomatic TB. However, diagnostic performance of transcriptomic and proteomic markers is weaker for asymptomatic TB than symptomatic TB, suggesting that policy development for community-based, asymptomatic TB screening should not adopt biomarkers developed for symptomatic TB triage without further optimization.

Background: High-risk subgroups among household contacts of persons with tuberculosis (TB) might benefit from additional interventions. However, the significance of an abnormal baseline chest radiograph (CXR) suggestive of TB, despite negative sputum microbiology, is uncertain. Methods: Adults (≥18 years) with recent household TB exposure were enrolled at three South African sites (April 2021– September 2022). All participants underwent symptom screening, CXR, and sputum Xpert Ultra and MGIT culture. Pulmonary TB diagnosis was microbiologically-confirmed. Participants without prevalent TB were followed for symptomatic incident TB through 12 months. Multivariable logistic regression identified factors associated with abnormal CXR suggestive of TB. Poisson regression estimated adjusted incidence rate ratios (aIRR) with 95% confidence intervals (95%CI). Results: Baseline CXR were available for 795/846 (94.0%) participants without prevalent TB and were abnormal in 157/795 (19.7%); associated with older age (adjusted odds ratio, aOR=1.04, 95%CI 1.02–1.05); prior TB (aOR=6.39, 95%CI 4.18–9.78); and current smoking (aOR=1.61, 95%CI 1.00–2.62). Symptomatic incident TB developed in 8/795 (1.0%) participants, including 7/8 (87.5%) who were asymptomatic and 4/8 (50.0%) with abnormal CXR at baseline. TB incidence was higher in those with abnormal versus normal CXR (aIRR=4.11, 95%CI 1.29–13.09), but after median 12.1 (IQR 11.1–13.1) months follow-up, 153/157 (97.5%) had not progressed to incident TB. Conclusions: Adult household contacts with CXR abnormalities, but without prevalent TB, had a four-fold higher incidence of TB within one year, compared to those with normal CXR. This additional risk warrants targeted preventive treatment and extended surveillance, but since most remained TB-free, therapeutic TB treatment is not justified. Key points: Adult household contacts with abnormal CXR have four-fold increased risk of incident TB disease compared to those with normal CXR, supporting targeted preventive treatment and extended surveillance. However, since the vast majority remain TB-free, therapeutic TB treatment is not warranted.

Background: The World Health Organisation (WHO) recommends digital chest radiography (dCXR) with computer-aided detection (CAD) for tuberculosis (TB) screening of individuals >15 years of age. Methodology: Adults (≥18 years) were enrolled (March 2021-December 2022) in South Africa into a community-based Screening Cohort (household contacts) and a facility-based Triage Cohort (symptomatic clinic attendees). Microbiologically-confirmed pulmonary TB required positive sputum culture and/or Xpert Ultra. Asymptomatic TB was diagnosed in participants without TB symptoms. dCXR were read by blinded human readers and qXR CAD (0.5 threshold; Qure.AI, India). Results: dCXR from 1,353 participants (886 Screening Cohort; 467 Triage Cohort) were analysed. Microbiologically-confirmed TB occurred in 48 (5.4%) Screening Cohort [9 symptomatic (19%) and 39 asymptomatic (81%)]; and 116 (24.8%) Triage Cohort (all symptomatic) participants. dCXR sensitivity (human readers) for asymptomatic TB in the Screening Cohort was 56.4%, vs. 72.4% for symptomatic TB in the Triage Cohort (difference -16%; 95%CI -2.9 to -29.1); with specificities 94.1% and 81.2%, respectively. Corresponding qXR CAD sensitivities were 69.2% vs. 83.6% (difference -14.4%; 95%CI -26 to –2.8), with specificities 89.3% and 73.5%, respectively. The difference in dCXR sensitivity and specificity for asymptomatic TB between qXR CAD and human readers was 12.8% (95%CI -0.48 to 26.1) and -4.8% (95%CI -12.4 to 28.2), respectively. Conclusion: Sensitivity of community-based dCXR screening for microbiologically-confirmed asymptomatic TB among household contacts was lower than for facility-based triage of symptomatic TB, but approached 70% with CAD. Neither human reader nor qXR CAD evaluation met WHO targets for a TB screening test (90% sensitivity; 80% specificity). Research in context: Evidence before this study: The World Health Organisation (WHO) recommends digital chest radiography (dCXR) with computer-aided detection (CAD) for tuberculosis (TB) screening of individuals >15 years of age, based on data from prevalence surveys and facility-based studies. Performance data for community-based screening of asymptomatic TB are lacking. We searched PubMed for literature published in English between January 1, 2000, and November 1, 2025, for community-based, active case-finding studies of adolescents and adults aged 15 years and older that used dCXR CAD for asymptomatic TB screening. We used the following search terms: “Tuberculosis” AND (“asymptomatic” OR “subclinical”) AND (“computer aided diagnosis” OR “artificial intelligence”) AND “community-based screening” AND “chest radiography” AND (“diagnostic performance” OR “sensitivity”). We identified five studies reporting on microbiologically-confirmed asymptomatic TB and dCXR CAD performance. Three of five studies tested sputum only in those who were symptomatic and/or had abnormal CXR. One study did measure prevalence of asymptomatic TB by universal sputum testing of all participants, but did not report sensitivity and specificity for asymptomatic TB separately. One case-control study of CAD4TB (v7), which pooled data from five active case-finding cohorts, reported sensitivity of 61.4% and specificity of 86.7% for asymptomatic TB. However, the case-control design and inclusion of two cohorts using prevalence survey methodology and three cohorts enrolling high TB risk groups, two of which did not perform CXR on all participants, suggest potential for selection bias. Added value of this study: We evaluated discriminatory performance of dCXR screening for asymptomatic TB among adult household contacts of TB patients, using human readers and qXR CAD (QURE.AI, India), in three communities in South Africa (Screening Cohort). Performance was benchmarked against that for symptomatic TB among adult clinic attendees (Triage Cohort), to enable comparison with traditional published approaches. All participants underwent universal sputum testing, regardless of symptom status or dCXR results. Sensitivity of human readers for asymptomatic TB in the Screening Cohort was 56.4%, compared to 72.4% for symptomatic TB in the Triage Cohort, with specificity 94.1% and 81.2%, respectively. The corresponding sensitivity of qXR CAD for asymptomatic TB, using the manufacturer’s 0.5 threshold score, was 69.2%, compared to 83.6% for symptomatic TB, with specificity 89.3% and 73.5%, respectively. The difference in dCXR sensitivity and specificity for asymptomatic TB between qXR CAD and human readers was 12.8% and -4.8%, respectively. The adjusted qXR threshold score (0.007) required to achieve 90% sensitivity for asymptomatic TB reduced specificity to 18.9%; and did not meet the WHO Target Product Profile (TPP) for a high sensitivity (90%), high specificity (80%) TB screening test. Implications of all the available evidence: Sensitivity of community-based dCXR screening of household contacts for asymptomatic TB was low, compared to facility-based triage of symptomatic TB. Neither human reader nor qXR CAD evaluation of dCXR met the minimal WHO TPP for a high sensitivity (90%), high specificity (80%) TB screening test. Although dCXR CAD community screening would detect more than two-thirds of all people with previously undiagnosed, microbiologically-confirmed asymptomatic TB, the significant proportion of people with TB that would remain undetected, and untreated, might allow ongoing Mycobacterium tuberculosis transmission and hinder elimination efforts.

Background: Tuberculosis (TB) remains a leading infectious cause of death globally. While control strategies have traditionally prioritized symptomatic cases, growing evidence highlights the substantial burden of asymptomatic or subclinical TB, microbiologically confirmed disease without classical symptoms, posing challenges for detection, treatment, and elimination efforts. Methods: We conducted a scoping review in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. We selected epidemiological studies, prevalence surveys, modeling analyses, and recent World Health Organization (WHO) guidance to summarize the current understanding of asymptomatic TB. We examined definitions, diagnostic approaches, transmission potential, natural history, and public health implications, with special focus on vulnerable populations. Results: Prevalence surveys reveal that up to 30%–50% of bacteriologically confirmed TB cases may be asymptomatic at diagnosis, many of whom remain undetected under symptom-based screening. A substantial fraction of these individuals is smear positive, underscoring their potential role in community transmission. Despite clinical silence, radiographic and molecular studies demonstrate ongoing lung pathology and immune activation, with 20%–30% progressing to symptomatic disease within 2 years. Diagnostic challenges include low bacillary burden and inability to expectorate sputum, though innovations, such as computer-aided radiography, sputum pooling, and host transcriptomic biomarkers, are advancing detection. Conclusions: Asymptomatic TB represents a hidden but consequential component of the TB disease spectrum. Recognition and integration of this stage into TB control frameworks are essential for accurate burden estimation, timely treatment, and achievement of elimination targets. Future efforts must focus on scalable diagnostics, biomarker validation, and equitable screening strategies tailored to vulnerable populations.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects nearly one-fourth of global population, with 5%–10% progressing to active TB, one of the deadliest infectious diseases worldwide. Despite advancements in identifying infected individuals, actual tools lack precision in identifying those at highest risk of active TB. Close contacts of TB cases are at particularly high risk of progression. Multinational networks, such RePORT (Regional Prospective Observational Research for TB) International—a consortium of eight country-based networks—have advanced the field through collaboration, data sharing, and large-scale studies across diverse populations. This review synthesizes current knowledge on TB transmission dynamics, biomarkers, and genetic factors influencing disease progression, predictive models for identifying high-risk individuals, and the implications for public health interventions and screening programs. By centering on findings from RePORT studies, we discuss the strengths and limitations of existing approaches, including the temporal dynamics and context dependence of host-response signatures, and consider key challenges for implementation in high-burden settings. Together, these insights highlight opportunities to refine targeted TB prevention strategies and advance progress toward TB elimination.