Treatment outcomes of Mycobacterium simiae pulmonary disease: a retrospective multicenter cohort study

Background: Mycobacterium simiae is an emerging cause of non-tuberculous mycobacterial pulmonary disease (NTM-PD) in the Middle East, yet treatment outcomes remain unclear. We aimed to evaluate clinical and microbiologic outcomes of M. simiae–PD. Methods: We performed a retrospective multicenter cohort study (2010–2022) including adults meeting ATS/IDSA criteria, stratified by treatment status. Clinical, microbiologic, and radiologic outcomes were compared. Results: Sixty-eight patients were included; 32 (47%) received antimicrobial therapy and 36 (53%) were untreated. Treated patients were younger, had lower BMI, and more symptoms. During follow-up, microbiologic eradication occurred in 44% (12/27) of treated vs. 85% (29/34) of untreated patients. Eradication was associated with higher BMI, non-smoking status, and absence of cavitary disease. Antimicrobial therapy did not improve eradication rates. Conclusions: Combined antimicrobial therapy for M. simiae–PD demonstrates poor microbiologic efficacy, highlighting the urgent need for more effective, targeted treatments.