Rat Bite Fever: It's Still a Threat.

Streptobacillus moniliformis is considered normal flora of the upper respiratory tract of rodents and is the predominant cause of rat bite fever in North America. Although patients with rat bite fever oftentimes present with migratory polyarthralgia, cultures of affected joints do not grow bacteria in the vast majority of cases. We present a case of a 32-year-old woman who initially presented with a painful, swollen right index finger proximal interphalangeal (PIP) joint following a bite from her pet rat. After initial treatment with empiric antibiotics did not clear the infection, PIP joint irrigation and debridement revealed culture-positive septic arthritis. This case illustrates the patient's unusual presentation of S. moniliformis infection through septic arthritis of the PIP joint.