Disseminated <i>Mycobacterium marinum</i> infection: diagnostic and therapeutic challenges in an immunocompromised host

<i>Mycobacterium marinum</i> causes a rare, slow-progressing zoonotic infection without distinctive clinical features. History of aquatic exposure increases clinical suspicion. We present a case of disseminated <i>M. marinum</i> infection which progressed from a localised cutaneous infection over 1.5 years. A delayed diagnosis, due in part to a low index of suspicion and underlying CD4 cytopenia, contributed to clinical deterioration. Despite numerous courses of antimicrobial therapy, the patient experienced treatment failure and ultimately succumbed to the disease. Notably, the patient had a longstanding history of traditional Chinese medicine (TCM) consumption, which was later found to contain corticosteroids, contributing to immunosuppression. This case underscores the complexities of diagnosing and managing <i>M. marinum</i> infection in immunocompromised individuals and highlights the importance of thorough medication history-taking, including the use of TCM. Greater awareness of TCM pharmacovigilance is also crucial in preventing inadvertent harm.