BACKGROUND Morbidity and mortality from nontuberculous mycobacterial pulmonary disease (NTM-PD) are increasing. Mycobacterium avium complex (MAC) is the most common cause of NTM-PD. Microbiological outcomes are widely used as the primary end point of antimicrobial treatment, but their long-term impact on prognosis is uncertain.

RESEARCH QUESTION Do patients who achieve microbiological cure at the end of treatment have longer survival than those who do not?

STUDY DESIGN AND METHODS We retrospectively analyzed adult patients who met the diagnostic criteria for NTM-PD, were infected with MAC species, and were treated with a macrolide-based regimen for ≥ 12 months per guidelines between January 2008 and May 2021 at a tertiary referral center. Mycobacterial culture was performed during antimicrobial treatment to assess the microbiological outcome. Patients with three or more consecutive negative cultures collected ≥ 4 weeks apart and no positive cultures until treatment completion were considered to have achieved microbiological cure. To assess the impact of microbiological cure on all-cause mortality, we performed multivariable Cox proportional hazards regression analysis adjusted for age, sex, BMI, presence of cavitary lesions, erythrocyte sedimentation rate, and underlying comorbid conditions.

RESULTS Among 382 patients enrolled, 236 (61.8%) achieved microbiological cure at completion of treatment. These patients were younger, had lower erythrocyte sedimentation rates, were less likely to use four or more drugs, and had shorter treatment duration than those who failed to achieve microbiological cure. During a median follow-up of 3.2 (first quartile to third quartile, 1.4-5.4) years after treatment completion, 53 patients died. Microbiological cure was significantly associated with reduced mortality after adjustment for major clinical factors (adjusted hazard ratio, 0.52; 95% CI, 0.28-0.94). The association between microbiological cure and mortality was maintained in a sensitivity analysis that included all patients treated < 12 months.

INTERPRETATION Microbiological cure at completion of treatment is associated with longer survival in patients with MAC-PD.