Disseminated Mycobacterium simiae infection causing rhinosinusitis in a severely immunocompromised patient

Mycobacterium simiae is a slow-growing environmental nontuberculous mycobacterium (NTM), commonly isolated from soil and water. M. simiae is not known to transmit zoonotically or via human-to-human contact; infection is presumed to occur through direct environmental exposure. Although M. simiae represents a small proportion of NTM isolates globally, its clinical relevance is increasingly recognized. Extrapulmonary manifestations are rare, and to date, no cases of rhinosinusitis attributable to M. simiae have been reported.

A 33-year-old male with advanced HIV (cluster of differentiation 4⁺ count 6 cells/µL), who completed tuberculosis treatment 2 months prior to the current admission, presented with right eye proptosis, pain, restricted ocular movement, nasal discharge, and fever. Three weeks earlier, he was hospitalized and discharged for chronic diarrhea complicated by acute-on-chronic kidney injury and pancytopenia. Imaging showed sinus opacification with bony erosion extending into the orbit. Cultures from blood and sinus aspirate identified Mycobacterium simiae, confirmed by line-probe assay. Despite multidisciplinary care, minimal improvement occurred, and he died 2 weeks after admission.

This case represents the first documented instance of M. simiae-associated rhinosinusitis and highlights the pathogenic potential of environmental NTM in causing destructive and disseminated disease in severely immunocompromised patients.