Estimating the global burden of viable Mycobacterium tuberculosis infection: A mathematical modelling study

Estimating the proportion of individuals currently infected with Mycobacterium tuberculosis (Mtb) is key for informing global health policies. Although a substantial portion of the global population exhibit tuberculous immunoreactivity, not all have a viable Mtb infection. Moreover, individuals with recent infections are at a higher risk of developing tuberculosis (TB). Here, we present estimates of the global burden of viable Mtb infection, using new insights into the natural history of TB.

We constructed country-specific trends in annual risk of infection considering estimates of TB burden, immunoreactivity reversion, and age-specific mixing. We applied these trends to a deterministic mathematical model incorporating reinfection and self-clearance to estimate recent (within 2 years) and total viable Mtb infections. Empirical data on self-clearance are limited, so rates were informed by modelling estimates. In 2022, we estimated that 133.7 million people (95% uncertainty interval [UI]: 104.0, 171.1) had a recent Mtb infection, representing 1.7% (95% UI: 1.3, 2.2) of the global population. In total, 288.9 million people (95% UI: 242.2, 342.7)-or 3.7% (95% UI: 3.1, 4.3) globally-were estimated to harbour a viable Mtb infection. Among those recently infected, 12.0% (95% UI: 11.4, 12.7) were children under 15 years of age. Most recent infections were found in the World Health Organization regions of South-East Asia (49.0%; 95% UI: 37.2, 62.4), the Western Pacific (19.7%; 95% UI: 12.6, 30.5), and Africa (17.9%; 95% UI: 12.9, 24.1). India, Indonesia, and China had the highest burden, with 39.1 million (95% UI: 18.0, 73.6), 12.0 million (95% UI: 5.8, 22.9), and 11.2 million (95% UI: 5.0, 25.5) people, respectively, recently infected with Mtb. Sensitivity analyses of varying self-clearance scenarios showed significant changes in global estimates of viable Mtb infection, particularly in total burden, with lower self-clearance rates. Overall uncertainty in the estimates was considerable, reflecting limitations in the underlying data informing key model parameters.

Our findings offer global burden estimates of viable Mtb infection and reveal a sizable population recently infected with Mtb and at high risk of progression to disease. New diagnostic tools that can detect individuals with viable Mtb-particularly those who would benefit from TB preventive therapy-are urgently needed.