Asymptomatic tuberculosis resists single tests, review argues for staged pathways

People with tuberculosis who report no symptoms at screening represent one of the most stubborn obstacles to disease control, and a new narrative review argues that the problem cannot be solved by any single test. Writing in Frontiers in Cellular and Infection Microbiology, researchers from institutions in China and Guangxi synthesize current evidence on how asymptomatic tuberculosis is defined, detected and misclassified, and conclude that effective diagnosis will require staged, risk-stratified pathways rather than standalone screening tools.

The review’s central conceptual point is that asymptomatic tuberculosis is a symptom-defined and method-dependent phenotype, not a uniform biological stage. Individuals classified as asymptomatic may carry minimal or extensive radiographic abnormalities, shed bacilli at low or intermittent levels, or harbor clinically inapparent disease that remains stable, regresses, fluctuates or progresses. Because terminology, symptom ascertainment, population risk and diagnostic intensity vary across studies and programs, estimates of how common asymptomatic disease is differ widely and cannot be compared directly.

That variability is visible in the numbers the authors compile. Across published studies, roughly 27 to 82 percent of prevalent tuberculosis has been classified as asymptomatic, depending largely on which symptom definition was applied. In a systematic review and meta-analysis of adolescents and young adults aged 10 to 24 years, the pooled prevalence of asymptomatic tuberculosis among those screened was 1 percent, yet 62 percent of diagnosed tuberculosis cases in that group were asymptomatic. An individual-participant-data meta-analysis of community prevalence surveys in adults found adjusted proportions of pulmonary tuberculosis without persistent cough, without any cough and without any reported tuberculosis-related symptoms of 82.8, 62.5 and 27.7 percent, respectively.

Symptom ascertainment itself is vulnerable to bias. In a Vietnamese active case-finding study, 64.8 percent of bacteriologically confirmed cases reported no respiratory symptoms before diagnosis, compared with 17.8 percent after diagnostic disclosure, despite some patients having smear-positive results, medium-level Xpert results or chest radiographs consistent with tuberculosis. In a Singapore registry of 18,693 people with culture-confirmed pulmonary tuberculosis, measured prevalence was 41.6 percent when the definition allowed cough of less than two weeks, but 31.6 percent when restricted to complete absence of cough. A review of 71 studies found that only 27 provided an explicit definition at all.

Conventional sputum-based testing faces its own constraints. Symptom-negative individuals often cannot produce spontaneous sputum, and children may require induced sputum, gastric aspiration or nasopharyngeal sampling. In a Swiss national surveillance study, only 34.9 percent of pediatric subclinical tuberculosis cases were microbiologically confirmed. Asymptomatic disease is often paucibacillary: in a nationwide Korean cohort, positivity rates for smear microscopy, mycobacterial culture and tuberculosis PCR in subclinical disease were 16.2, 50.2 and 33.8 percent, compared with 35.9, 66.3 and 56.9 percent in symptomatic disease, and a Chinese multicenter study reported a similar pattern. The pattern is not universal, however; among untreated South African people living with HIV, smear positivity was numerically higher in subclinical than symptomatic tuberculosis, a difference that was not statistically significant.

Imaging adds capacity but not certainty. Chest radiography can reveal abnormalities in symptom-negative individuals, yet a normal radiograph does not exclude active disease: among asymptomatic adults with HIV and tuberculosis in Cape Town, 10 of 14 who underwent chest radiography had normal findings, and in a Canadian cohort of culture-positive subclinical pulmonary tuberculosis, 17.5 percent had a normal radiograph. Computed tomography was substantially more sensitive than radiography for cavitation, endobronchial spread, lymph-node enlargement and bilateral disease in that cohort, but interpretation suffers from poor reproducibility, and PET/CT misclassified 44 percent of tuberculosis cases as lung cancer in one 57-patient cohort. Computer-aided detection can standardize triage at scale, but in a pooled analysis of five South African community screening studies, CAD4TB v7 achieved an overall area under the curve of 0.83, performed less well in asymptomatic than symptomatic individuals, and at 90 percent sensitivity reached only 44.9 percent specificity, failing to meet the World Health Organization target product profile for a screening or triage test.

Non-sputum pathogen assays and host biomarkers are promising because they reduce dependence on spontaneous sputum, but most remain insufficiently validated. A tongue-swab high-volume quantitative PCR assay in South Africa showed a sensitivity of only 35.1 percent for asymptomatic tuberculosis, falling to 19 percent among participants with low or trace bacillary grades. Transcriptomic signatures performed modestly: in an individual-participant-data analysis of 6,530 samples, five single-gene transcripts achieved areas under the curve of 0.75 to 0.77 in distinguishing subclinical tuberculosis from people who remained disease-free, none meeting the WHO minimum target for a progression test. Serum C-reactive protein poorly distinguished asymptomatic tuberculosis from healthy contacts in South African household contacts, with an area under the curve of 0.60, and a promising two-protein panel was limited by elevation of both proteins in non-tuberculosis pulmonary diseases.

The review also emphasizes that diagnostic strategy is a question of program design and resource allocation. In South African household contacts, universal sputum testing identified 18 asymptomatic cases that symptom- or radiography-triggered investigation would have missed, increasing diagnostic yield by 54.5 percent, but broader screening increases demands for imaging, specimen collection, molecular testing, referral and follow-up while generating more false positives. In Vietnam, computer-aided detection followed by Xpert testing among people who inject drugs raised sensitivity from 43.9 to 82.9 percent but reduced positive predictive value to 54.0 percent and increased the cost per case detected from 309 to 439 US dollars. Among household contacts of patients with rifampicin-resistant tuberculosis, routine testing of a single sputum sample detected only 7 of 23 prevalent cases, and 30 to 35 percent of people flagged by computer-aided detection but not diagnosed by routine testing were later diagnosed through enhanced investigation, meaning they should not automatically be treated as false positives.

The authors are explicit about the limitations of their own synthesis. The review was informed by a targeted, non-systematic PubMed search rather than a systematic review or meta-analysis, so relevant studies may have been missed and the evidence is susceptible to selection bias. Much of the evidence on computed tomography characterization, blood-based host signatures, computer-aided screening and PET/CT derives from adult populations and cannot be assumed to apply to children, in whom symptom assessment, specimen acquisition, microbiological confirmation and radiographic interpretation differ substantially; inter-observer agreement for hilar lymphadenopathy on pediatric chest radiographs has been poor.

The review’s conclusion is that the diagnostic challenge lies not simply in the absence of symptoms but in the unstable boundary between infection, early disease, radiological abnormality, microbiological detectability and future risk. It proposes staged pathways that integrate symptom ascertainment, exposure risk, imaging, confirmatory microbiology, enhanced specimen collection and longitudinal reassessment, with explicit escalation, referral, follow-up and exit criteria. Such frameworks, the authors stress, should be viewed as flexible clinical-programmatic tools for organizing diagnostic uncertainty and generating testable hypotheses, not as validated treatment algorithms, and priority research areas include standardized symptom definitions, prospective characterization of natural history, direct measurement of infectiousness and evaluation of complete diagnostic and management pathways in the settings where they are intended to be used.

Subject of Research: Diagnosis of asymptomatic and subclinical tuberculosis

Article Title: Diagnosing asymptomatic tuberculosis: current approaches, emerging tools, and persistent challenges

Article References: Wang, M.-S., Wei, D.-Y., Liu, X.-H., & Zhang, Z.-F. (2026). Diagnosing asymptomatic tuberculosis: current approaches, emerging tools, and persistent challenges. Frontiers in Cellular and Infection Microbiology, 16, 1935260. https://doi.org/10.3389/fcimb.2026.1935260

Image Credits: AI Generated

DOI: 10.3389/fcimb.2026.1935260

Keywords: asymptomatic tuberculosis, subclinical tuberculosis, active case finding, chest radiography, computer-aided detection, sputum testing, host biomarkers, PET/CT, Xpert MTB/RIF, diagnostic pathways, tuberculosis screening, paucibacillary disease