Probable Pasteurella multocida Osteomyelitis Following a Cat Bite: A Case Report

Pasteurella multocida is a Gram-negative coccobacillus that commonly colonizes the oral cavity of cats and dogs and is an important cause of skin and soft tissue infections following animal bites. Invasive infections such as osteomyelitis are uncommon. We report a case of probable osteomyelitis caused by P. multocida following a cat bite. A 60-year-old woman presented to the emergency department after being bitten on the distal interphalangeal region of the second finger of her right hand by a cat. Initial plain radiography showed no bone abnormalities. Rabies and tetanus prophylaxis was administered, and empirical oral antimicrobial therapy with amoxicillin–clavulanate and azithromycin was initiated. Three days later, she developed progressive erythema and swelling at the wound site despite the initial treatment, and the antimicrobial regimen was switched to oral trimethoprim–sulfamethoxazole. Two weeks later, fluctuant swelling and purulent drainage developed. Follow-up radiography demonstrated osteolytic changes in the distal aspect of the middle phalanx, suggestive of probable osteomyelitis, and magnetic resonance imaging showed findings consistent with osteomyelitis involving the articular surfaces of the middle and distal phalanges at the distal interphalangeal joint. Culture of the purulent material yielded Pasteurella multocida, identified using the Phoenix automated identification system. Antimicrobial susceptibility testing demonstrated susceptibility to penicillin, ampicillin, amoxicillin–clavulanate, trimethoprim–sulfamethoxazole, levofloxacin, and ciprofloxacin. Based on the clinical, radiographic, magnetic resonance imaging, and microbiological findings, the patient was considered to have probable P. multocida osteomyelitis. As the isolate was susceptible to trimethoprim–sulfamethoxazole, the same antimicrobial regimen was continued, and treatment was planned for a total duration of six weeks.This case emphasizes that normal initial radiographs do not exclude osteomyelitis and highlights the importance of repeated imaging and microbiological evaluation in patients with progressive hand infections following cat bites.