Microbiological Characteristics of Extrapulmonary Nontuberculous Mycobacterial Infections in a Tertiary Hospital

Objective To analyze the microbiological characteristics of extrapulmonary nontuberculous mycobacterial (ENTM) infections in a tertiary hospital and to provide data to support clinical diagnosis and treatment of ENTM infections.

Methods A retrospective analysis was conducted on mycobacterial culture results from West China Hospital, Sichuan University from 2020 to 2023. A total of 68 confirmed cases of ENTM infection were enrolled, with all of which meeting the diagnostic criteria for extrapulmonary infection outlined in the Guidelines for the Diagnosis and Treatment of Nontuberculous Mycobacterial Disease (2020). Demographic data, strain distribution, and drug susceptibility test results were analyzed. Microbial species identification was performed using mass spectrometry, and drug susceptibility was assessed using the microbroth microdilution method.

Results Among the 68 ENTM cases, the male-to-female ratio was 1 to 1.2, with individuals aged 40-59 years being the main affected group population. The most common sites of infection were the skin and soft tissues. The primary specimen source was pus (33.8%, 23 cases), followed by pathological tissues (26.5%, 18 cases). The Department of Infectious Diseases was the main source of confirmed cases (29.4%, 20 cases). Among the 68 EMTM cases, rapid-growing mycobacteria (RGM) accounted for 32.4% (22 cases), with Mycobacterium abscessus being the predominant species, while slowly-growing mycobacteria (SGM) accounted for 67.6% (46 cases), with Mycobacterium intracellulare and Mycobacterium marinum being the predominant species. RRGM exhibited higher minimum inhibitory concentration (MICs) for rifampicin and rifabutin but lower MICs for clarithromycin and amikacin. In contrast, SGM demonstrated low MICs for most antibiotics tested.

Conclusion In this study, ENTM infections most commonly involve the skin and soft tissues, with SGM being the predominant pathogens and Mycobacterium intracellulare being the dominant species. RGM shows susceptibility to clarithromycin and amikacin, which provides a basis for empirical anti-infective therapy. Although SGM exhibits low MICs to most tested antimicrobial agents, combination regimens remain necessary in clinical practice, and the risk of treatment failure should be thoroughly evaluated.