Poster Presentations: Tuesday, October 25, 2011 |

Evaluation of QuantiFERON-TB Gold Assay (QFG-IT) in Detection of Latent and Active Infection With Mycobacterium tuberculosis in a Group of Egyptian Children FREE TO VIEW

Maha Ghanem, MD; Hebat Allah Rashed, MD; Nefesa Refaat, MD
Chest. 2011;140(4_MeetingAbstracts):381A. doi:10.1378/chest.1118587
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PURPOSE: to evaluate the performance of QFG-IT assay compared to Tuberculin Skin Test (TST)in the diagnosis of latent TB infection (LTBI) and active tuberculosis (TB) in a cohort of Egyptian children.

METHODS: In a tertiary hospital-based prospective study, the diagnostic accuracy of the tuberculin skin testing (TST) and QFG-IT were assessed in a cohort of 112 children (mean age 6.98(4.44), range (0.7-16). The cohort included 3 groups; group 1:control not exposed children (n=20), group II: exposed children investigated for LTBI (n=42), group III: children investigated for active TB (n=50).

RESULTS: For confirmed active TB, TST was positive in 24 out of 26 cases (92.31%), compared to 37 out of 50 cases (74%) for QFG-IT. None of the 2 tests performed significantly better than the other (p=0.109). The agreement between the 2 tests in the whole cohort was good (84.21%, κ 0.677). The agreement between QFG-IT and TST in confirmed TB was fair in 20 out of 25 cases at 80% (κ 0.365). In latent TB infection (LTBI), TST was positive in 14 out of 34 cases (41.18%), compared to 8 out of 42 cases (19.05%) for QFG-IT. Despite that QFG-IT performed better than TST; this difference did not reach statistical significance (p=0.063). The agreement between QFG-IT and TST was moderate (78.13%, κ 0.509); eight cases (7.14%) of the QFG-IT showed indeterminate results. Significantly higher number of positive QFG-IT and TST were seen among children older than 5 years compared to children aged 5 years or less (p=0.009, and 0.007, consecutively).

CONCLUSIONS: QTG-IT did not show higher diagnostic value in confirmed active childhood TB. Both QFG-IT and TST perform better in children older than 5 years than in younger population. The fair to moderate agreement between positive QFG-IT and active and latent TB disease suggests its good sensitivity. Discrepancies between QFG-IT and TST can be a result of higher specificity of QFG-IT that is not influenced by previous BCG vaccination.

CLINICAL IMPLICATIONS: Although positive QFG-IT supports the diagnosis of TB in TST positive children, negative QFG-IT does not exclude active TB. If used for diagnosis of LTBI, QFG-IT could significantly reduce the numbers of children receiving chemoprophylaxis.

DISCLOSURE: The following authors have nothing to disclose: Maha Ghanem, Hebat Allah Rashed, Nefesa Refaat

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