Clinical usefulness of QuantiFERON TB-2G test for the early diagnosis of pulmonary Mycobacterium kansasii disease.

We encountered five cases of pulmonary Mycobacterium kansasii (MK) disease for which the QuantiFERON-TB Gold (QFT-2G) test was useful as a supportive diagnostic method. Because none of these patients could expectorate sputum, we ultimately confirmed the clinical diagnosis of pulmonary MK disease using 6- to 8-week cultures of bronchoscopic specimens (bronchoalveolar lavage fluid) according to the guidelines for nontuberculous mycobacterial disease due to American Thoracic Society/Infectious Diseases Society of America. The tuberculin skin test showed positive responses in all cases, and the QFT-2G test showed positive response for ESAT-6 only or CFP-10 only antigens. After it was proved that the result of Mycobacterium tuberculosis (MTB)-nucleic acid amplification was negative and the result of the QFT-2G test was positive, we started treatment (isoniazid, rifampicin and ethambutol) for suspected pulmonary MK disease based on clinical findings in all cases. The clinical effect was good and the interferon-gamma response to MTB-specific antigen decreased with treatment for pulmonary MK disease. The QFT-2G test may be useful as a rapid supportive diagnostic method for pulmonary infection due to MK possessing the same MTB-specific antigen.