Streptobacillus moniliformis septic arthritis: a clinical entity distinct from rat-bite fever?

BACKGROUND Streptobacillus moniliformis is a zoonotic agent associated with rodent contacts. Although it is more commonly reported to cause rat-bite fever with reactive arthritides, it can also lead to pyogenic infection of the joints. CASE PRESENTATION We present a lady with past history of osteoarthritis developing streptobacillary septic arthritides of the right knee and left wrist, and required antibiotic and arthrotomy for treatment. We also review 11 previously reported cases of streptobacillary septic arthritis to discuss the characteristics, treatment, prognosis of the infection, and illustrates the differences between streptobacillary rat-bite fever and septic arthritis. Among this patient population, most patients had potential contact with rats (91.6%). The knee is the most commonly affected joint (58.3%), and 83.3% patients having polyarticular involvement. As opposed to rat-bite fever, fever and rash was only present in 58.3% and 16.7% of patients respectively. S. moniliformis bacteremia is uncommon (8.4%) and the prognosis is good. CONCLUSION Arthrocentesis is useful in distinguishing streptobacillary septic arthritis from reactive arthritis of rat-bite fever. The sole use of commercial media containing sodium polyanethol sulfonate may render the bacterial culture negative. A detailed history of possible exposure to rodents should be elicited from patients with arthritis in order to facilitate microbiologic diagnosis.