Streptobacillus moniliformis bacteremia in an afebrile patient: A rare case report

Rat-bite fever (RBF), caused by Streptobacillus moniliformis, typically presents with fever, rash, and polyarthralgia, but we report an atypical afebrile case in a 36-year-old woman who presented with severe arthralgia and purpuric rash without fever. Laboratory findings revealed leukocytosis, elevated inflammatory markers (CRP 118.77 mg/L, ESR 64 mm/h), and acute kidney injury. Two sets of blood cultures grew Streptobacillus moniliformis, identified by Gram stain, colony morphology, and MALDI-TOF mass spectrometry (Bruker system, score 2.50). Antimicrobial susceptibility testing, performed according to CLSI M100 guidelines, demonstrated sensitivity to penicillin (MIC 0.032 mg/L), ceftriaxone, and other antibiotics. The patient was treated with intravenous penicillin (1.6 million units every 8 h for 14 days) and showed clinical improvement before discharge. This case underscores that fever may be absent in RBF and highlights that, in patients with compatible symptoms (e.g., rash, arthralgia) and potential rodent exposure, blood cultures should be considered even in the absence of fever, especially when other infectious or inflammatory causes are being evaluated, to avoid diagnostic delay.