Mixed Mycobacterium kansasii and Mycobacterium smegmatis infection in an adult-onset immunodeficiency patient with anti-interferon-γ autoantibodies.

Anti-interferon-gamma autoantibody (AIGA) is a rare adult-onset immunodeficiency disease that increases the risk of occult infection. Nontuberculous mycobacteria (NTM) infections represent a diverse group of species and subspecies, and mixed infections with two or more NTM species have been reported. However, there is no consensus on the optimal antibiotics or immune modulator treatments for mixed NTM infections in AIGA patients. Here, we present the case of a 40-year-old female who initially presented with suspected lung cancer with obstructive pneumonitis. Tissue samples obtained through bronchoscopy, endoscopy, and bone marrow biopsy revealed disseminated mycobacterium infection. PCR-based testing confirmed a mixed pulmonary infection with Mycobacterium kansasii and Mycobacterium smegmatis , as well as M. kansasii bacteremia. The patient received 12 months of anti-NTM medications for M. kansasii , and the symptoms improved. Additionally, the images showed resolution after 6 months, even without the need for immune modulator treatment.