Rat-bite fever laboratory tests

Diagnosis
The findings of rash, fever, and arthritis in individuals with a history of rat exposure suggest the diagnosis of Rat-bite fever.

Diagnosis of S. moniliformis is typically made by isolating the organism from blood or synovial fluid. Specific media and incubation conditions should be used. In the absence of a positive culture, identification of pleomorphic gram-negative bacilli in appropriate specimens supports a preliminary diagnosis. Since the organism does not grow in artificial media, diagnosis of S. minus is made by identifying characteristic spirochetes in appropriate specimens using darkfield microscopy or differential stains.