Older adults carry the largest undetected TB burden, yet community case-finding is not designed to find it

Question: What do active case-finding and community-based screening interventions show about tuberculosis case detection and yield in older adults compared with younger age groups in high-burden settings?

Answer

Taken together, the retrieved papers support a position that is more indirect — and more uncomfortable — than a simple yield comparison: no study in this set reports age-stratified yield or number-needed-to-screen from an active case-finding (ACF) intervention, so the field has not actually measured whether community screening finds proportionally more TB in older than younger adults. What the evidence does establish is that the burden gradient points steeply upward with age while the detection gradient points downward: bacteriologically confirmed TB prevalence rises ~30% per decade of age and notification-to-prevalence ratios fall ~10% per decade, meaning older adults are the most systematically under-detected group relative to their true prevalence [5]. In parallel, the tools that community ACF actually deploys — symptom screening, chest radiography, sputum-dependent molecular testing — perform worst precisely on the low-bacillary, asymptomatic, paucibacillary phenotype that dominates community-detected disease [16] [8], and ACF programmes name migrants, people living with HIV, drug users and contacts as their priority risk groups, not older adults [15]. The defensible synthesis is therefore that the expected yield per person screened should be highest in the oldest age bands, but realised yield is depressed by both programme design and tool performance, and the trials that would settle this have not reported the age-disaggregated data needed to do so.

TB prevalence and detection gaps both scale with age, in opposite directions

Age is not a modest risk modifier: across 82 population-based surveys in 30 countries and 4.6 million participants, each 10-year increase in age was associated with a 30% (95% CrI 22–38) increase in bacteriologically confirmed pulmonary TB prevalence, with the 75+ group at 796 per 100,000 versus 127 per 100,000 at ages 15–19 — a 6.4-fold difference [5]. Positive age gradients were present in every country, though attenuated in Africa relative to other regions and flatter above age 40 in countries with HIV prevalence ≥5% [5].

The same analysis shows the detection gap widens with age rather than narrowing: notification-to-prevalence ratios declined by 10% (7–14) per 10-year increase in age, the authors' proxy for untreated, diagnostically delayed TB [5]. This is the quantitative core of the case for age-targeted ACF — the largest absolute pool of undiagnosed disease sits in the oldest age bands even where the relative age gradient is shallow.

Transmission modelling adds a second justification: contributions to TB transmission were flatter or increasing with age across settings, and the analysis flags an "under-appreciated contribution to transmission in some settings from older adults, who may face particular barriers to healthcare access" [4]. Older adults are therefore not only prevalent-but-missed cases but potential ongoing sources in some epidemiological contexts.

Deployed ACF programmes prioritise other risk groups and report yield without age breakdown

Community-wide annual symptom screening in 21 Zambian and South African communities produced newly diagnosed TB yields of 81, 93 and 110 per 100,000 across three rounds in Zambia and 380 per 100,000 in South Africa, with higher yield in men, newly diagnosed HIV-positive individuals and first-time screenees; the authors concluded that yield was "relatively low compared to estimated TB prevalence" [3]. None of the determinants reported there is age, so the largest single trial of repeated community TB screening cannot answer whether older adults were over- or under-detected [3].

The umbrella review of ACF versus passive case finding found ACF more effective in high-risk populations explicitly enumerated as migrants, people living with HIV, drug users and close contacts, with cost-effectiveness in high-prevalence settings but limited evidence of sustained notification gains [15]. Older adults are absent from that enumerated priority list — a mismatch with the prevalence evidence above.

Targeting logic itself is well supported, even if the targeting variable is not age: in Blantyre, an ACF approach covering 48% of the population was estimated to identify 80% of all people with TB at US$1,100 per DALY averted versus US$1,600 for untargeted ACF, though both exceeded Malawi's thresholds [6]. Test sensitivity, more than specimen logistics or turnaround, drove the largest gains in treatment initiation in a comparable ACF model [10].

Symptom and radiograph screening lose sensitivity exactly where older-age disease sits

Among 979 TB-exposed household contacts, prevalent TB was asymptomatic in 82.4% of cases, and abnormal CXR detected only 56.1% of asymptomatic cases versus 88.9% of symptomatic ones, with symptom-plus-CXR sensitivity of 64.0% overall [16]. Community-based digital CXR with CAD achieved 69.2% sensitivity for asymptomatic community-detected TB versus 83.6% for facility-based symptomatic triage, and neither human reading nor qXR met WHO's 90%/80% targets [7].

Molecular tools degrade in the same direction: tongue swab qPCR sensitivity was 34.1% in community household screening versus 63.8% in clinic triage, and 35.1% for asymptomatic TB specifically [8]. Pooled Xpert Ultra testing lost more sensitivity in community-based than facility-based case finding (59.1% vs 84.0%) [9], and community testing detects disproportionately paucibacillary disease [14].

The closest available proxy to an older-adult screening population is a diabetes clinic cohort (median age 54): symptom screening sensitivity was 22.2% and CXR 55.6%, with CXR specificity falling to 87.6% in those with prior TB versus 97.2% without [17]. Both poor symptom sensitivity and prior-TB-related radiographic ambiguity are properties that will be more common, not less, in older screening populations. Host biomarkers do not rescue this: CRP and IL-6 were elevated in asymptomatic community-detected TB but neither performed adequately as a diagnostic [21].

Where age is modelled explicitly it is the dominant signal, and age-stratified thresholds help modestly

In a harmonised dataset of 169,813 people from four community prevalence surveys in South Africa and Zambia, an XGBoost model identified age, previous TB treatment, number of treatments and unemployment as the primary contributors to TB risk, and achieved 81.5% sensitivity at 60% specificity against 38.2% for the WHO four-symptom screen [11]. That symptom screening's sensitivity is roughly 38% in community populations, while age is the top-ranked predictor, is the strongest available argument that age-based eligibility would outperform symptom-based eligibility.

Age-stratified operational thresholds produce real but small gains: among 52,835 Ugandan participants screened with portable CXR and CAD, stratifying X-ray score thresholds by age and sex raised estimated sensitivity from 75.0% to 76.9% at 96.1% specificity (p=0.046) [19]. Older age was also independently associated with abnormal baseline CXR among household contacts (aOR 1.04 per year), and abnormal CXR carried a four-fold higher incidence of incident TB (IRR 4.02) [2].

Higher yield in older adults would not automatically translate into benefit

Patients over 60 had 4.3-fold odds of unsuccessful TB treatment outcome (95% CI 2.11–10.1) in national Bhutanese surveillance data, prompting the authors to call for active follow-up of elderly patients [18]. Older age is consistently reported as a host-related factor associated with TB severity across 117 studies [1], and immunopathology work in mice shows slower Mtb clearance after treatment initiation in old and aged animals despite comparable mycobacterial loads during early infection [20]. Any yield advantage from screening older adults must therefore be paired with linkage and adherence provisions, and yield-per-100,000 is an incomplete metric.

Conflicts and gaps

The central conflict is one of prioritisation rather than of data: prevalence evidence identifies older adults as the group with the largest detection deficit [5], while the ACF evidence base and its umbrella synthesis define high-risk targeting in terms of HIV, migration, drug use and contact status without reference to age [15]. No retrieved paper adjudicates between these framings.

Second, the screening-tool validation studies that would underpin age-targeted ACF enrol populations that are far too young to inform it: median age 39 among 909 household contacts [12], median 37 among 1,168 presumptive-TB participants across four countries [13], and median 39 in the paired tongue-swab evaluation [8]. Reported diagnostic accuracy is therefore estimated largely in people under 50, while the population with highest prevalence is over 60.

Third, the geographic qualification matters and is unresolved: age gradients are flatter in Africa and above age 40 where HIV prevalence is ≥5% [5], so the yield advantage of age-targeting in the highest-burden African settings may be substantially smaller than in Asian high-burden settings where steep gradients dominate. No retrieved ACF cost-effectiveness analysis stratifies by age, so the incremental cost per DALY of adding a 60+ eligibility criterion is unknown.

Fourth, whether older adults detected by ACF are infectious enough for transmission impact remains contested: modelling suggests non-trivial and under-appreciated transmission contribution from older adults in some settings [4], while ACF impact modelling attributes mortality and transmission gains primarily to confirmatory test sensitivity rather than to which subgroup is screened [10].

What would change the answer

An age-stratified secondary analysis of the PopART trial data — yield, number needed to screen, and pre-treatment loss to follow-up in 10-year bands — would immediately convert the current indirect inference into direct evidence [3]. A cluster-randomised ACF trial in a high-burden Asian and a high-HIV African setting, comparing community outreach restricted to adults ≥60 using CXR-CAD plus symptom-agnostic molecular testing against standard all-age symptom-based screening, with DALYs and treatment completion as co-primary outcomes, would settle both the yield and the benefit question. Extending age- and sex-stratified CAD threshold work to cohorts with high prior-TB prevalence, where CXR specificity falls to 87.6% [17], is needed before CAD-based 60+ screening is programmatically defensible, and prospective head-to-head specimen evaluations of tongue swab and pooled Xpert [9] powered to detect differences in the 60+ stratum would close the accuracy gap.

References

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How this survey was made

This survey answers one question: “What do active case-finding and community-based screening interventions show about tuberculosis case detection and yield in older adults compared with younger age groups in high-burden settings?”

We keep our own collection of recent preprints and refresh it every day from bioRxiv, medRxiv, arXiv, PsyArXiv, SocArXiv and ChemRxiv. For each survey, we search that collection for recent work and keep the strongest matches: papers that use the same terms as the question, and papers on the same topic in different words.

The text was written from the titles and abstracts of those papers; the full texts were not read. Statements that draw on a particular paper are marked with a number in brackets. The reference list just above is the 21 papers whose work this text draws on, chosen from the 73 papers those searches returned; the rest of the shortlist is not printed. It is not a complete review of everything published on the question.

Treat this as a starting point and a reading list, not a peer-reviewed review. The searches behind this survey ran on October 22, 2026 and covered work from the previous two years.