Distinguishing tuberculosis from Mycobacterium avium complex disease using an interferon-gamma release assay

Area of Science:

• Infectious Diseases
• Microbiology
• Immunology

Background:

• Distinguishing tuberculosis (TB) from non-tuberculous mycobacterial disease is crucial, particularly in areas with high TB prevalence.
• Interferon Gamma Release Assays (IGRAs), including QuantiFERON-TB Gold (QFT-G) and its predecessor QuantiFERON-TB (QFT), are used alongside the Tuberculin Skin Test (TST) for TB diagnosis.
• Challenges arise when differentiating active TB from Mycobacterium avium complex (MAC) disease due to overlapping immune responses.

Purpose of the Study:

• To evaluate the diagnostic utility of TST, QFT-G, and QFT in differentiating active TB from MAC lung disease.
• To assess the performance of these diagnostic tools in an intermediate TB burden country.

Main Methods:

• A prospective study comparing the diagnostic performance of TST, QFT-G, and QFT.
• Inclusion of 38 patients with confirmed TB and 40 patients with confirmed MAC lung disease.
• Analysis of test accuracy, sensitivity, and specificity for TB diagnosis.

Main Results:

• TST showed positive results in 70.6% of TB patients and 47.5% of MAC patients.
• QFT-G yielded positive results in 89.5% of TB patients and 34.3% of MAC patients.
• QFT showed positive results in 86.8% of TB patients and 35.3% of MAC patients, with similar overall accuracy, sensitivity, and specificity across all three tests for TB diagnosis.

Conclusions:

• The TST and IGRAs (QFT-G and QFT) demonstrated similar diagnostic accuracy for TB.
• These tests were unable to reliably discriminate between active TB and MAC disease.
• The findings suggest limitations of TST and IGRAs in differentiating active TB from MAC disease in TB-endemic settings.