Identifying emerging pathogens is vital for effective disease management. This report describes a case of pulmonary mycobacteriosis caused by *Mycobacterium triplex*, a recently described slowly growing nontuberculous mycobacterium. The patient, from Finland, presented with a pulmonary infection. The infecting strain was similar to the type strain but exhibited slight differences from the species description, prompting its classification as a variant of *M. triplex* sensu stricto. The patient was successfully treated with antimycobacterial drugs. The report highlights the importance of accurate identification of mycobacterial species in clinical settings, especially in cases of pulmonary infections. The ability to differentiate between typical and variant strains enables tailored treatment approaches. Ultimately, this case underscores the ongoing evolution of nontuberculous mycobacteria and the need for continued vigilance in identifying emerging pathogens. The identification led to a successful medical outcome. According to present knowledge, this variant of the species had never been isolated before the **infection**.
This case report, published in the Journal of Clinical Microbiology, is highly relevant to the journal's focus on the identification, diagnosis, and treatment of microbial infections. By presenting a unique case of pulmonary infection caused by a variant of Mycobacterium triplex, the report highlights the challenges in clinical microbiology and contributes to the understanding of emerging pathogens, a key area of interest for the journal. The study has implications for both medicine and microbiology.