Usefulness of Interferon-gamma Release Assays in the Diagnosis of Tuberculosis Infection in Hiv-infected Patients in Bulgaria

We aimed to evaluate the usefulness of incorporating the result from an IFN-gamma release assay (IGRA) in the algorithm for initial diagnosis of tuberculosis (TB) in prospectively enrolled HIV-infected subjects. Ninety HIV-infected subjects with clinical and/or radiological features consistent with a possible diagnosis of active-TB were tested with QuantiFERON®-TB Gold InTube (QFT) and T-SPOT.TBTM (SPOT). All information, including IGRA results, was available to clinicians for making their diagnosis. Those diagnosed with TB were given anti-TB treatment and samples were collected for microbiological culture. Overall, 35/90 patients were QFT positive and 30/90 by SPOT. QFT was indeterminate for 5/90 subjects (5.5%) and SPOT for 11/90 (12.2%; p=0.0313). Active-TB was microbiologically confirmed in 13 subjects and twelve (92%) were positive by QFT and one was negative. For SPOT, 8/12 (62%; p=0.125) were positive, onenegative, and 4 were indeterminate. Of the 77 HIV-positive subjects without microbiologically confirmed active-TB, 23 (30%) were positive, 49 (64%) negative, and 5 (6%) indeterminate by QFT, compared with 22 (29%), 48 (62%) and 7 (9%) by SPOT. Those IGRA positive, and two who were IGRA indeterminate, had a final presumptive diagnosis of active-TB, based upon initial clinical symptoms and improvement with antiTB treatment. All IGRA negative subjects had a diagnosis other than tuberculosis and none have since developed active TB over a period of more than 12 month. In conclusion, both IGRAs provided useful additional information for assisting the diagnosis and early treatment of Mycobacterium tuberculosis infection in immunocompromised HIV/AIDS patients with negative smear microscopy. A positive IGRA result was a significant factor in making initial diagnoses of TB, diagnoses that were later supported by clinical outcome following anti-TB therapy, and diagnoses other than TB in those IGRA negative. The QFT and SPOT tests had similar high sensitivity, with QFT having fewer indeterminate results, in our HIV-infected immunocompromised population.