Why a Mycobacterium Avium Infected Patient Showed a Positive Xpert MTB/RIF Result?

This article discusses whether a MAC infected patient with a positive Xpert MTB/RIF test has a co-infection with Mycobacterium tuberculosis (MTB). The patient presented with chronic, indolent pulmonary patchy shadows on imaging but lacked typical symptoms. The MTB antigen-specific interferon-gamma enzyme-linked immunospot assay (T-SPOT.TB) was negative. Bronchoalveolar lavage fluid (BALF) testing yielded conflicting results: Xpert MTB/RIF assay detected trace levels of MTB DNA, whereas reverse dot blot hybridization confirmed the presence of Mycobacterium avium complex (MAC); in contrast, metagenomic next-generation sequencing (mNGS) returned a negative result for all pathogens. Mycobacterial culture ultimately returned positive; however, the MPB64 assay-employed for species identification-yielded a negative result, indicating a probable nontuberculous mycobacterial (NTM) infection. Despite contradictory lab results, the patient's symptoms and culture findings favored MAC infection. However, MTB infection could not be definitively ruled out in this patient, so a treatment regimen combining anti-tuberculosis and anti-MAC medications (isoniazid, rifampicin, ethambutol, and azithromycin) was initiated, leading to significant radiographic improvement. The discordance between the positive Xpert MTB/RIF result and other diagnostic evidence highlights important diagnostic challenges, underscoring the need for integrated clinical interpretation and providing actionable insights for clinicians.