C68-11 A ‘‘Karius’’ Case of Mycobacterium Kansasii: When Bal and Blood Tell the Same Story

Abstract Introduction Mycobacterium kansasii is a slow-growing nontuberculous mycobacterium (NTM) that typically causes chronic pulmonary infection, most often in patients with underlying lung disease or immunocompromised. Diagnosis relies on microbiologic confirmation through acid-fast bacilli (AFB) smear and culture of respiratory specimens, most commonly bronchoalveolar lavage (BAL) fluid. Plasma metagenomic next-generation sequencing (mNGS) assays, such as the Karius cell-free DNA (cfDNA) test, offer a rapid, noninvasive method to detect microbial DNA fragments in circulation. However, their role in NTM infection remains poorly defined, and no prior cases have reported concurrent detection of M. kansasii by both BAL culture and plasma cfDNA. Case Presentation A 54-year-old previously healthy lifetime nonsmoker presented with a several-year history of progressively worsening dry cough that evolved into coughing fits and hemoptysis. Chest imaging revealed a 5 cm thick-walled right upper lobe cavity with surrounding tree-in-bud opacities. Bronchoscopy with BAL showed necrotizing granulomatous inflammation and was PCR-positive for Mycobacterium species (excluding M. avium complex and M. abscessus), though AFB smear was negative. Concurrently, plasma mNGS testing (Karius cfDNA assay) detected Mycobacterium kansasii. Given the extent of cavitary disease and persistent symptoms, combination antimicrobial therapy with intravenous amikacin and oral azithromycin, rifampin, and ethambutol was initiated per ATS guidelines. After 40 days, BAL cultures grew M. kansasii, confirming concordance between BAL and plasma findings. Discussion To our knowledge, this represents the first reported case of M. kansasii detected simultaneously by BAL culture and plasma cfDNA testing. Detection of M. kansasii cfDNA in an immunocompetent patient with localized pulmonary disease suggests that circulating microbial DNA may be present even without disseminated infection. While BAL culture remains the gold standard for species identification, its prolonged turnaround often delays therapy. In contrast, plasma mNGS can provide rapid, noninvasive results that may guide early management. This case demonstrates how cfDNA detection can complement traditional culture-based methods, potentially expediting diagnosis, and treatment in NTM infections. Conclusion This case highlights the diagnostic value of plasma mNGS in Mycobacterium kansasii pulmonary disease, even in immunocompetent hosts. Concordant detection by BAL and plasma cfDNA underscores the complementary role of molecular assays in the timely identification of nontuberculous mycobacterial infections. This abstract is funded by: None