Atypical rat bite fever associated with knee joint infection in a Chinese patient: a case report.

BACKGROUND

Rat bite fever (RBF) is a rare zoonosis transmitted from rodents to humans through bites and scratches. However, diagnosis and treatment of atypical clinical cases can be challenging.

CASE PRESENTATION: Herein, we report an atypical case of RBF with unilateral knee joint infection caused by Streptobacillus moniliformis. Streptobacillus moniliformis was isolated from the knee synovial fluid of the patient via microbiological culture and metagenomic next-generation sequencing (mNGS). After treatment with antibiotics and arthroscopic surgery, the patient reported symptom alleviation and was subsequently discharged home. This is the first reported detection of intraarticular histopathological changes caused by Streptobacillus moniliformis during knee arthroscopy.

CONCLUSIONS

In atypical cases, importantly, clinical healthcare professionals should promptly obtain microbiological culture results. When culture is negative, 16S ribosomal RNA gene polymerase chain reaction (16S rRNA PCR) or mNGS can be considered for identification, with inquiring about the patient's disease history, including any contact with rodents. Surgical interventions, such as arthroscopy, may be included in treatment. Streptobacillus moniliformis infection should be considered when considerable fibrous connective tissue and capillary proliferation are observed under arthroscopic guidance.