The global prevalence of tuberculosis infection

What is it about?

In 1999, the World Health Organization estimated that one-third of the world’s population had latent tuberculosis infection (LTBI) i.e. infected but without symptoms or signs of tuberculosis (TB). Recently, this estimate has been updated to one-fourth. However, this estimate remains based on controversial assumptions in combination with tuberculin skin test (TST) surveys - an older test with several shortcomings. Interferon-gamma release assays (IGRAs), newer tests with a higher precision, have since been widely implemented, but never used to estimate the global LTBI prevalence. We conducted a systematic investigation of all available literature on LTBI estimates based on both IGRA and TST results published between 2005 and 2018. Regional and global estimates of LTBI prevalence were calculated. Countries were divided by the incidence of TB in low, intermediate and high, respectively. An overall estimate for each area as well as a global estimate was calculated using a mathematical method. Out of 3280 screened studies, we included 88 studies from 36 countries with 41 IGRA (67 167 study subjects) and 67 TST estimates (284 644 study subjects). The global prevalence of LTBI was 24.8% and 21.2% based on IGRA and TST results, respectively, confirming that approximately one-fourth to one-fifth of the world's population is infected with the bacteria.

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Photo by freestocks.org on Unsplash

Photo by freestocks.org on Unsplash

Why is it important?

The study uses a new approach based on epidemiological evidence of latent tuberculosis and shows that it will be extremely difficult to meet the World Health Organization target of tuberculosis elimination by 2035. Further, the study documents a significant occurrence of tuberculosis infection in the world today although slightly less than previously thought. In this first study of the global prevalence of LTBI derived from both IGRA and TST surveys, we found that one-fourth of the world’s population is infected with TB. This is of high relevance as both tests, although imperfect, are used to identify individuals eligible for preventive therapy. Enhanced efforts are needed targeting the large pool of latently infected, as these individuals constitutes an enormous source of potential active TB in the future.

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