Estimated global prevalence of latent TB about 25%
About one-quarter of the world’s population may be infected with latent tuberculosis, according to a systematic review and meta-analysis published in the European Respiratory Journal.
Unlike previous WHO estimates, which relied solely on tuberculin skin tests for diagnosis, these findings were based on both skin tests and commercial interferon-gamma release assays (IGRAs). These tests, when compared with the skin tests, have shown higher specificity in diagnosing latent TB infection, the researchers noted.
Using several databases, the researchers identified studies published from 2005 to 2018 that reported on the prevalence of latent TB diagnosed by tuberculin skin test or IGRA. They then calculated prevalence of latent TB infection at the regional and global levels.
Eighty-eight studies from 36 countries qualified for inclusion in the analysis. When using IGRA for diagnosis, the global prevalence of latent TB infection was 24.8% (95% CI, 19.7-29.9). When using tuberculin skin test with a 10-mm cutoff, the global prevalence was 21.2% (95% CI, 17.9-24.4). The researchers also identified strong relationships between WHO TB incidence rates and latent TB prevalence based on both IGRA (Rs = 0.706; P < .0001) and tuberculin skin tests (Rs = 0.697; P < .0001).
The researchers also calculated global latent TB prevalence using several scenarios. For prevalence based on IGRA, the global prevalence of latent TB infection was 24.2% (95% CI, 19.2-29.2) when indeterminate results were counted as negative and 26.3% (95% CI, 21-31.6) when indeterminate results were counted as positive. For prevalence based on tuberculin skin test, the global prevalence was 24.1% (95% CI, 20.2-28) when a 5-mm cutoff was used and 17.4% (95% CI, 14.4-20.4) when a 15-mm cutoff was used.
In an analysis of the 20 studies that used IGRA and tuberculin skin tests concurrently, the global latent TB prevalence estimate based on IGRA was 25.2% (95% CI, 19.8-30.7) after exclusion of indeterminate results, vs. 27.1% (95% CI, 18.9-35.3) based on tuberculin skin test with a 10-mm cutoff.
These estimated global latent TB prevalences are considerably lower than the 1999 WHO estimate, which suggested that one-third of the world’s population had latent TB infection, and they are closer to an updated 2016 WHO estimate of 23%.
“We estimate one-fourth of the world’s population to be latently infected with TB, in the first study applying both IGRA and [tuberculin skin test] surveys,” the researchers wrote, noting that latent TB infection “still represents an enormous reservoir of potential reactivated TB and this must be recognized as a considerable obstacle, and as a point of intervention, in reaching The End TB Strategy goals of 2050.” – by Melissa Foster
Disclosures: This study was supported by the Novo Nordisk Foundation, the Swedish Research Council and the Swedish Heart and Lung Foundation. The authors report no relevant financial disclosures.