Chest X-rays Fail to Detect Asymptomatic TB Cases, Finds Lancet Global Health Study
New Delhi, October 28 (The Trending People): Chest X-rays and symptom-based screening, commonly used to detect tuberculosis (TB), are proving insufficient to identify asymptomatic infections among household contacts, according to a new study published in The Lancet Global Health. The research underscores the urgent need to improve TB detection strategies, particularly in countries where the disease burden remains high.
Study Highlights Gaps in TB Detection
The study, conducted by researchers from the University of Cape Town, South Africa, systematically screened 979 household contacts of patients diagnosed with pulmonary tuberculosis across three South African communities. Unlike conventional methods that rely heavily on reported symptoms and X-rays, the team used universal sputum microbiological testing, which remains the gold standard for TB confirmation.
When comparing the effectiveness of various screening methods, the researchers found that chest radiographs — often considered a reliable tool — failed to detect 40 per cent of confirmed TB cases.
The findings reveal that 5.2 per cent of all screened household contacts tested positive for pulmonary TB. Alarmingly, 82.4 per cent of those confirmed cases showed no symptoms at all. This means that most TB-positive individuals would have been missed entirely if screening had depended only on visible symptoms or X-rays.
“Over 80% of TB Cases Are Asymptomatic,” Says Lead Author
Dr Simon C. Mendelsohn, corresponding author of the study and a researcher with the South African Tuberculosis Vaccine Initiative, said the results challenge long-standing public health strategies.
“More than 80 per cent of confirmed people with tuberculosis among household contacts were asymptomatic; chest radiograph screening missed more than 40 per cent of these,” said Mendelsohn.
He emphasized that this diagnostic gap has far-reaching implications for global TB control efforts, especially in endemic regions.
“Community prevalence surveys reliant on symptom-based and chest radiograph-based approaches might substantially underestimate the prevalence of asymptomatic tuberculosis in endemic countries,” he added.
WHO’s Warning on “Missing Millions”
The World Health Organization (WHO) estimates that in 2023, nearly 2.7 million people, or 25 per cent of the world’s total 10.8 million TB cases, went undiagnosed or untreated. The organization has repeatedly stressed that finding and treating these “missing millions” is critical to achieving the global goal of eliminating TB by 2030.
However, identifying these cases remains a formidable challenge because a majority of them are asymptomatic — individuals infected with the TB bacterium but who show no outward signs of the disease.
According to the Lancet study, “More than half of all tuberculosis found in community prevalence surveys has been classified as asymptomatic, occurring in people who do not have, recognise, or report typical tuberculosis symptoms such as cough, fever, night sweats, and loss of weight.”
Chest X-rays and Symptoms Alone Fall Short
The study’s data show that chest X-ray screening detected only 56.1 per cent of asymptomatic TB cases. When combined with symptom-based checks, the overall sensitivity rose modestly to 64 per cent, still far below the WHO target for TB screening tests — a minimum 90 per cent sensitivity and 70 per cent specificity.
Researchers also noted that asymptomatic TB cases in household contacts tended to have a lower bacterial load and low serum C-reactive protein (CRP) levels, which made them indistinguishable from healthy individuals in standard medical testing. This further highlights why many infections go unnoticed until they progress to more severe stages.
“These findings indicate that the conventional reliance on chest radiographs and self-reported symptoms fails to meet the WHO’s target product profile for an effective tuberculosis screening test,” the study stated.
The Importance of Universal Sputum Testing
The research team stressed the need to adopt universal sputum microbiological testing, even in community-level screenings, to accurately capture asymptomatic TB cases.
Dr Mendelsohn said that national tuberculosis prevalence surveys that skip this universal sputum testing “might substantially underestimate the true prevalence of asymptomatic tuberculosis in high-burden countries.”
He added that improving diagnostic sensitivity through molecular tests or portable microbiological tools could transform early detection, prevent household transmission, and reduce the global TB load.
Implications for Public Health Policy
Public health experts believe that the study’s results could prompt a reassessment of TB screening strategies worldwide. While chest X-rays remain a low-cost, accessible tool in developing countries, they clearly lack the sensitivity needed to detect early-stage or symptomless infections.
Given the scale of the global TB epidemic, experts argue that relying solely on such methods may perpetuate the underdiagnosis of millions. Integrating molecular testing, such as GeneXpert, or AI-assisted radiography into public health programs could enhance accuracy, but these technologies are often limited by cost and infrastructure constraints.
Moreover, the study emphasizes that household contacts — people who live with TB patients — represent a particularly high-risk group that requires active, not passive, surveillance. Without improved screening protocols, asymptomatic carriers could unknowingly contribute to ongoing transmission within communities.
Global TB Burden: The Road Ahead
Tuberculosis continues to be one of the world’s top infectious killers, claiming over 1.3 million lives annually. Despite decades of control programs, progress toward eradication has been slow.
WHO has called for intensified case finding, the use of new diagnostic tools, and investment in vaccine development to address both latent and active TB. Researchers like Mendelsohn believe that redefining “screening” itself — from symptom checks to microbiological testing — is a critical first step.
Countries with high TB prevalence, such as India, Indonesia, China, Nigeria, and South Africa, could especially benefit from updating their national TB detection frameworks.
What the Study Means for India
India accounts for the highest number of TB cases globally, making this study particularly relevant for policymakers and healthcare workers. Current screening programs in India often rely on chest X-rays and symptom-based community drives, which could be missing a significant proportion of asymptomatic carriers.
Public health experts say India must strengthen its diagnostic chain — from primary health centres to district-level labs — to include universal testing where feasible. As the nation moves toward its goal of eliminating TB by 2025, improving early detection of asymptomatic infections will be essential to break the transmission cycle.
Final Thoughts from The Trending People
The findings published in The Lancet Global Health serve as a crucial wake-up call for the global health community. The revelation that chest X-rays and symptom-based screenings miss nearly half of asymptomatic TB cases underscores the need for more accurate and inclusive diagnostic approaches.
For nations like India, where TB remains a leading public health challenge, these results demand immediate action — through stronger surveillance, better access to sputum testing, and continuous investment in diagnostic innovation.
As the world pushes toward the goal of ending TB by 2030, bridging this diagnostic gap could determine whether that vision becomes reality or remains a distant goal.