Pasteurella multocida infectious arthritis.

Pasteurella multocida, a small gram-negative rod, is a domestic animal saprophyte that occasionally causes disease in humans. Infectious arthritis may develop from a superficial animal bite or scratch. Nine previous cases of infectious arthritis due to this organism have been documented in the literature, and a tenth case is reported here. Most patients had recent animal exposure, and half the patients had underlying chronic rheumatoid arthritis. Clinical signs of inflammation were consistently present; however, systemic infection was infrequent. The lack of positive synovial fluid gram-stain smears may make differentiation from other forms of infectious arthritis difficult. Penicillin in moderate doses is effective therapy, with osteomyelitis developing in only two patients. The tendency for this syndrome to affect patients with rheumatoid arthritis may reflect deficient local defense mechanisms, chronic steroid therapy, or increased ownership of pets. The mechanism of spread of infection to the joint space appears to be through contiguous spread from a skin site rather than by the hematogenous route in most cases.