Immediate Treatment Versus Watchful Waiting in Mycobacterium avium Complex Pulmonary Disease: A Propensity Score Matched Analysis.

INTRODUCTION: The optimal timing for initiating antibiotic therapy in Mycobacterium avium complex pulmonary disease (MAC-PD) remains controversial. While previous studies advocate for "watchful waiting" in some cases, specific criteria to prioritize immediate treatment over observation are not well defined. METHODS: We retrospectively analyzed 592 treatment-naïve patients with MAC-PD diagnosed between 2003 and 2021. Propensity score matching was used to balance baseline characteristics between patients receiving immediate treatment (initiated ≤ 2 months [60 days] of diagnosis) and those undergoing watchful waiting. Primary outcomes were all-cause and respiratory mortality; secondary outcomes included culture conversion and adverse events. RESULTS: After matching, 102 pairs were analyzed. Immediate treatment was associated with significantly faster culture conversion [hazard ratio (HR) 3.07; 95% CI 1.68-5.61] but a higher incidence of adverse events (64.7% vs. 41.2%; P = 0.001). In the overall matched population, immediate treatment did not improve all-cause (HR 0.92; 95% CI 0.53-1.61) or respiratory mortality (HR 0.47; 95% CI 0.19-1.14). However, in the subgroup of patients with moderate-to-severe disease (BACES score ≥ 2), immediate treatment was significantly associated with reduced all-cause (HR 0.53; 95% CI 0.30-0.96) and respiratory mortality (HR 0.35; 95% CI 0.14-0.90). CONCLUSIONS: Immediate treatment accelerates culture conversion but increases AEs without improving overall survival, supporting watchful waiting for mild cases. However, patients with a BACES score ≥ 2 derive significant survival benefit from immediate therapy, suggesting the BACES score is an effective tool for guiding treatment timing. Regardless of the initial treatment decision, close and regular monitoring remains essential, as some patients will ultimately require treatment.