Multifocal pyogenic arthritis and osteomyelitis with bacteremia caused by Streptobacillus notomytis: A case report and comprehensive literature review.

Streptobacillus notomytis, recently recognized as a distinct species from Streptobacillus moniliformis-the primary causative agent of rat-bite fever-has been implicated in rare human infections. To date, there are no documented cases of femoral and tibial osteomyelitis attributable to this pathogen. Herein, we report a case of multifocal pyogenic arthritis and osteomyelitis involving the femur and tibia with bacteremia caused by S. notomytis, alongside a review of human infections associated with this organism. A 73-year-old woman initially presented with left knee pain at another hospital, where a filamentous gram-negative bacillus was isolated from joint aspirate and blood cultures. After developing sepsis, she was transferred to our facility. On admission, she had tenderness in both shoulder joints and swelling in the right fingers and wrist. Arthroscopic lavage was performed, and empirical antibiotics were initiated. Further analysis of the original isolates using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) identified S. moniliformis with a low confidence score of 1.6. Magnetic resonance imaging confirmed osteomyelitis of the femur and tibia. After 9 weeks of targeted therapy, the patient fully recovered ambulatory function. Subsequent 16S rRNA gene sequencing definitively identified the pathogen as S. notomytis. These findings highlighted that in cases of pyogenic arthritis with unclear etiology and potential rodent exposure, Streptobacillus spp., including S. notomytis, should be considered. Comprehensive diagnostics, including 16S rRNA sequencing, are essential for accurate pathogen identification, and careful monitoring for complications like osteomyelitis is crucial during management.