Discordance between TST and QFT-TBGold Plus for Latent Tuberculosis Screening among Under-Five Children: An Interim Analysis.

AIM: To analyze the agreement between tuberculin skin test (TST) and fourth-generation QuantiFERON (QFT)-TB Gold Plus [interferon gamma (INF-γ) release assays (IGRA)] for latent tuberculosis infection (LTBI) diagnosis among under-five children who are undernourished and/or who have history of contact with active tuberculosis (TB) patients. METHODS: Children from the age group of 6 months to 5 years (undernourished or tuberculosis household contacts) were screened through anganwadis (government playschools) and TB Health posts from Mumbai, India during September 2019 to January 2021. Both TST and QFT-TB Gold Plus test were carried out to diagnose LTBI. RESULTS: Out of the total 299, 35 (11.7%) (95% CI 8.1-15.3%) children tested positive by IGRA (QFT-TB Gold Plus) and 68 (22.7%) (95% CI 18.0-27.4%) by TST, suggestive of moderate concordance (κ = 0.483) between both tests. IGRA and TST showed moderate concordance in children <24 months (κ = 0.478). Moreover, 26 (21.1%) children with TB contact had both TST and IGRA positive with moderate concordance (κ = 0.550). A fair concordance (κ = 0.396) was observed between IGRA and TST in undernourished children. Also, 45 (15.0%) children showed discordance of which 39 (13.0%) had positive TST but negative IGRA and 6 (2.0%) had negative TST but positive IGRA. CONCLUSIONS: The study strongly recommends both TST and QFT-TB Gold Plus test for the diagnosis of LTBI in under-five children. A moderate concordance in children <24 months endorses the reliability of QFT-TB Gold Plus in diagnosing LTBI in this age group. This study highlights the need for screening undernourished children for LTBI to consider repeating IGRA testing for TST positives as per the window period and risk of ongoing exposure.

The current study focuses on discordance and concordance between tuberculin skin test (TST) and fourth-generation QuantiFERON (QFT)-TB Gold Plus [interferon gamma (INF-γ) release assays (IGRA)] for latent tuberculosis infection (LTBI) diagnosis among at-risk under-five children who are underweight and/or who have history of contact with active tuberculosis patients. The IGRA prevalence came out to be 11.7% (95% CI 8.1­15.3%) whereas the TST prevalence turned out to be 22.7% (95% CI 18.0­27.4%). A stronger concordance was observed between IGRA and TST among the age group of 2 to 5 years, and a relatively fair one for children below the age of 1 year. The present study strongly recommends to include both TST and IGRA test for the diagnosis of LTBI with respect to Indian pediatric population. This study also suggests the importance of repetition of IGRA for TST positive patients. Another vital opinion that is showcased in the present study is the inclusion of undernourished pediatric population residing in at-risk areas like urban slums for routine LTBI screening programs.