Trends of tuberculin skin test positivity rate among schoolchildren in Attica, Greece

Evaluating a 24-year tuberculosis screening in first-grade elementary schoolers in a low-burden area

AIM

Early diagnosis of tuberculosis infection can significantly contribute to the control of the disease. The aim of the present study was to describe the tuberculin skin test (TST) trends over a 24-year period (1990-2013) and explore the value of universal tuberculosis screening in a low-burden area.

METHODS

All first graders that underwent TST during the 24-year study period (1990-2013) on the island of Crete, Greece, were retrospectively included in the study.

RESULTS

A total of 82 402 children (92.3% of Greek nationality; 51.0% male) underwent TST, of whom 335 (0.41%, 95% CI 0.37-0.46) were found to have positive TST while 0.27% of the study population had a TST between 5 and 9 mm. The tuberculin index declined significantly between 1990-1994 and 2010-2013 (0.67 vs 0.26; RR 2.73, 95% CI 1.82-4.09; p < 0.0001). Positive TST result was significantly higher in the immigrant than the native group (0.66% vs 0.24%; RR 3.76 95%, CI 2.89-4.84; p < 0.0001). In the last study years, 386 children (488 native; 153 immigrant) should be tested for one to be found TST positive.

CONCLUSION

Our findings question the massive tuberculin testing in low-burden areas and point to selective screening of high-risk groups.

The global prevalence of latent tuberculosis: a systematic review and meta-analysis

In 1999, the World Health Organization (WHO) estimated that one-third of the world's population had latent tuberculosis infection (LTBI), which was recently updated to one-fourth. However, this is still based on controversial assumptions in combination with tuberculin skin test (TST) surveys. Interferon-γ release assays (IGRAs) with a higher specificity than TST have since been widely implemented, but never used to estimate the global LTBI prevalence.We conducted a systematic review and meta-analysis of LTBI estimates based on both IGRA and TST results published between 2005 and 2018. Regional and global estimates of LTBI prevalence were calculated. Stratification was performed for low, intermediate and high TB incidence countries and a pooled estimate for each area was calculated using a random effects model.Among 3280 studies screened, we included 88 studies from 36 countries with 41 IGRA (n=67 167) and 67 TST estimates (n=284 644). The global prevalence of LTBI was 24.8% (95% CI 19.7-30.0%) and 21.2% (95% CI 17.9-24.4%), based on IGRA and a 10-mm TST cut-off, respectively. The prevalence estimates correlated well to WHO incidence rates (Rs=0.70, p<0.001).In the 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. This is of 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 individuals, as this constitutes an enormous source of potential active tuberculosis.