Clinical Characteristics and Mortality of Primary Nontuberculous Mycobacterial Bacteremia: A Retrospective Cohort Study

Abstract Purpose: The incidence of nontuberculous mycobacteria (NTM) infection has been rising, yet primary NTM bloodstream infections are not well understood. This study evaluates the risk factors, clinical presentations, and outcomes of NTM bacteremia in patients treated at a medical center over the past seven years. Materials and Methods: Between 2018 and 2024, patients with positive blood cultures for NTM were included from 2018 to 2024 at a medical center in Northern Taiwan. Primary bacteremia was defined as the absence of any NTM infection source outside the bloodstream. Clinical characteristics, disease severity, treatment approaches, and outcomes were documented. Factors related to in-hospital mortality were also analyzed. Results: Among 32 patients identified with NTM bloodstream infections, 15 (46.9%) had an identifiable infection focus, and 17 (53.1%) were classified as having primary bacteremia. Patients with primary NTM bacteremia were older (median age 68, IQR 59-86) compared to the non-primary group (median age 55, IQR 31-74) (p = 0.027) and had a higher body mass index (BMI) (24.94 vs 21.26, p=0.073) and a lower prevalence of acquired immunodeficiency syndrome (AIDS) (0% vs 33%, p=0.015). Primary NTM bacteremia was more commonly caused by rapidly growing NTM, such as Mycobacterium abscessus and M. chelonae (94.1% vs 53.3%, p=0.013), and less frequently by M. avium complex (5.9% vs 40.0%, p=0.033). Patients in the primary bacteremia group were less often treated with macrolide-based therapy (23.5% vs 93.3%, p<0.001) and had a higher in-hospital mortality rate (47.1% vs 6.7%, p=0.018). Among the primary NTM bacteremia group, 2 (11.8%) patients received treatment prior to blood culture collection, compared to 5 (33.3%) in the non-primary group. Kaplan-Meier analysis demonstrated higher mortality rates for primary NTM bacteremia (Log Rank test, p = 0.046). Within the mortality group, a higher proportion of patients had primary NTM bacteremia (88.9% vs 39.1%, p=0.018) and were more frequently infected with rapid growing species (100% vs 65.2%, p=0.070). After adjusting for age>60 years, sex and NTM species, primary NTM bacteremia was independently associated with in-hospital mortality (OR 12.02, 95% CI 1.12-129.18, p=0.04). Conclusions: Patients with primary NTM bacteremia were typically older, had a lower prevalence of AIDS and more frequently infected with rapid growing NTM species. Primary NTM bacteremia, less often treated with macrolide-based therapy, was independently associated with a 12-fold increased risk of in-hospital mortality. To improve patient outcomes, further studies are necessary to explore timely treatment strategies for NTM bacteremia without a clear infection focus.