T-SPOT.TB Test® results in adults with Mycobacterium avium complex pulmonary disease

The tuberculin skin test is limited by its inability to distinguish between infection with Mycobacterium tuberculosis and non-tuberculous mycobacteria (NTM). Newer interferon-gamma release assays using ESAT-6 and CFP-10 antigens should have a higher specificity for tuberculosis but have not been widely tested in adults with pulmonary disease due to NTM. In this study, we tested the T-SPOT.TB Test in patients with pulmonary disease due to Mycobacterium avium complex (MAC), the most common disease-causing NTM. Fourteen patients with prior culture-confirmed pulmonary disease due to MAC, 10 patients with prior culture-confirmed tuberculosis and 4 healthy controls were interviewed and tested with the T-SPOT.TB Test. 13 patients with MAC disease and 4 healthy subjects (negative controls) had non-reactive T-SPOT.TB results and 10 patients with prior tuberculosis (positive controls) had reactive results. One patient with MAC disease had a minimally reactive result on initial testing and a non-reactive result on re-testing. The T-SPOT.TB Test had a specificity of 94% for distinguishing between patients with prior MAC disease and prior tuberculosis disease, and will be useful in low tuberculosis prevalence settings where most mycobacterial infections are due to MAC. Reactions to the T-SPOT.TB Test may persist months to years after treatment of tuberculosis.