Lebanon Maps Its Hidden Tuberculosis Infection Burden to Rebuild National Screening

Tuberculosis may be the world’s most famous infectious disease, yet the quiet reservoir that keeps it alive is not the coughing patient in a clinic but the hundreds of millions of people carrying the bacterium without any symptoms at all. A new cross-sectional study from Lebanon, published in BMC Infectious Diseases, has now measured that hidden reservoir in the country’s highest-burden regions and found that the tools used to detect it tell strikingly different stories depending on who is being tested. The findings arrive at a pivotal moment for a country whose health system has been battered by economic collapse and population displacement, and they could directly reshape how Lebanon screens for tuberculosis infection in the years ahead.

The research, led by Josette Najjar-Pellet of the Mérieux Foundation together with colleagues from the Lebanese Ministry of Public Health, Saint Joseph University of Beirut, and collaborating hospitals, set out to do something Lebanon had not systematically done before: quantify tuberculosis infection, or TBI, among the populations considered most at risk in Beirut and Mount Lebanon, the two governorates bearing the country’s heaviest tuberculosis burden. Between September 2019 and June 2023, the team screened 860 participants drawn from four groups: healthcare workers, household and close contacts of active tuberculosis cases, migrants, and prisoners. Every participant underwent either the century-old Tuberculin Skin Test, the newer QuantiFERON-TB Gold Plus interferon-gamma release assay, or both, allowing the researchers to compare how the two diagnostic philosophies performed head to head in a real-world setting.

The headline numbers are sobering. Overall positivity for the skin test stood at 24.9 percent, while the blood-based assay returned positive results in 20.9 percent of those screened. In other words, roughly one in four people tested in these at-risk groups carried evidence of tuberculosis infection. But the aggregate figures conceal the study’s most consequential discovery: the burden is not distributed evenly. Migrants and tuberculosis contacts showed the highest prevalence of infection by a clear margin, confirming that Lebanon’s epidemic is concentrated in precisely the populations least likely to be reached by routine passive case finding. Healthcare workers, despite their occupational exposure, and prisoners occupied a lower tier of measured infection in this cohort.

That concentration matters because tuberculosis infection is the raw material of future epidemics. When Mycobacterium tuberculosis settles into a person’s lungs, it can persist in a dormant state for decades, held in check by the immune system until something—HIV infection, immunosuppressive therapy, diabetes, malnutrition, or simply the passage of time—tips the balance. Between 5 and 10 percent of infected people who never receive preventive treatment will eventually develop active disease, and each active case becomes a new engine of transmission. Screening for infection is therefore not an academic exercise; it is the front line of tuberculosis elimination, identifying the people who would benefit most from preventive therapy before they ever become contagious.

The two screening tools embody fundamentally different approaches to detecting that dormant infection. The Tuberculin Skin Test relies on a delayed-type hypersensitivity reaction: purified protein derivative, a cocktail of mycobacterial antigens, is injected into the skin, and the immune response is read as a zone of induration 48 to 72 hours later. It is cheap and requires no laboratory, but it cross-reacts with the Bacille Calmette-Guérin vaccine and with nontuberculous mycobacteria, and it demands a return visit for accurate reading. The QuantiFERON assay takes the opposite route: a blood sample is exposed to mycobacterial antigens in the laboratory, and the release of interferon-gamma by sensitized T cells is measured directly. It is more specific, unaffected by BCG vaccination, and requires only a single visit, but it costs more and depends on laboratory infrastructure that must process the sample within hours.

When the Lebanese team compared the two tests across their four population groups, the agreement between them proved anything but uniform. Kappa statistics, which measure how well two tests concur beyond what chance alone would produce, ranged from fair at 0.33 among tuberculosis contacts to moderate at 0.60 among migrants. The discrepancies were most notable among migrants and prisoners, the very groups where BCG vaccination histories, prior exposure to environmental mycobacteria, and nutritional or immunological factors are most likely to diverge from the general population. This is not a technical footnote. It means that a single national screening algorithm, applied identically to everyone, would systematically miss infections in some groups while overcalling them in others, wasting scarce resources and leaving the most vulnerable unprotected.

The multivariate logistic regression analysis sharpened the picture further. Being a tuberculosis contact emerged as the strongest independent risk factor, with an adjusted odds ratio reaching up to 5.9 for a positive result on at least one test. Migrant status carried an adjusted odds ratio of 1.8, a smaller but still meaningful elevation. These figures quantify what public health officials have long suspected but had never before measured with this precision in Lebanon: the epidemic’s future cases are already identifiable today, concentrated among people who share households or air with active cases and among displaced populations carrying infection burdens from higher-prevalence settings.

The study’s practical implications for Lebanon’s National Tuberculosis Programme are direct. Rather than a one-size-fits-all national algorithm, the data argue for tailored screening strategies matched to each population group. For tuberculosis contacts, where the skin test’s fair agreement with the blood assay suggests it may under-detect infection, the interferon-gamma release assay’s superior specificity and single-visit convenience could justify the added cost. For migrants, where the two tests agreed moderately but discrepancies remained common, the choice of test may hinge on vaccination history and the practical realities of reaching a mobile population. For healthcare workers and prisoners, the lower measured prevalence suggests that existing occupational screening may already be capturing much of the burden, though the authors caution that their convenience sampling in two governorates means these estimates describe the sampled groups rather than the nation as a whole.

The timing of this research is significant for a country navigating extraordinary pressures. Lebanon’s economic collapse has strained every layer of its health infrastructure, from medicine supply chains to laboratory reagents, while the influx and movement of displaced populations has altered the epidemiological landscape faster than surveillance systems could adapt. The study’s co-funding by the Fondation Mérieux and QIAGEN, with laboratory support from the Rodolphe Mérieux Laboratory at Saint Joseph University, reflects the kind of international partnership that has kept essential diagnostics functioning through the crisis. The collaboration with nongovernmental organizations including Amel Association International and Caritas Lebanon, and with the International Organization for Migration, was essential for reaching populations that formal health services rarely touch.

What makes this study resonate beyond Lebanon’s borders is its methodological honesty. The authors do not claim nationally representative prevalence figures; they explicitly state that their targeted convenience sampling in two governorates produces estimates that describe the sampled groups alone. Yet the study’s core finding—that screening test performance and infection burden vary systematically by population group—applies to any country designing a tuberculosis elimination strategy. As the World Health Organization pushes member states toward elimination targets, the Lebanese data offer a template: measure the burden in each at-risk population, compare the available diagnostic tools in that same population, and build the national algorithm from the ground up rather than imposing it from the top down. For a disease that has accompanied humanity for millennia, the path to elimination may depend less on any single breakthrough than on this kind of granular, population-specific evidence.

Subject of Research: Tuberculosis infection affects roughly one in four people screened in Lebanon's highest-burden regions, with contacts and migrants at greatest risk, according to a new cross-sectional study that could reshape the country's national screening strategy.

Article Title: Cross-sectional study toward optimizing the national screening strategy for tuberculosis infection in Lebanon

Article References: Cross-sectional study toward optimizing the national screening strategy for tuberculosis infection in Lebanon. (n.d.). https://doi.org/10.1186/s12879-026-14460-7

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14460-7

Keywords: tuberculosis infection, tuberculin skin test, interferon-gamma release assay, QuantiFERON-TB Gold Plus, Lebanon, national screening strategy, high-risk populations, TB contacts, migrants, prisoners, healthcare workers, BMC Infectious Diseases