Cat Bite Infection

Cat bite infection is bacterial infection of a puncture wound inflicted by a cat's teeth or claws, with Pasteurella multocida in over half of cases. Narrow, deep punctures seed bacteria into tendon sheaths, joints and bone, so infection is more frequent (30 to 50 percent) than for dog bites.

• Other organisms: Staphylococcus aureus, streptococci, anaerobes, Capnocytophaga, Bartonella henselae (cat scratch disease), Francisella tularensis (rare).
• Rabies is a risk in Kenya.

Pain, swelling, erythema and purulent drainage within 12 to 24 hours of the bite (Pasteurella), often on the hand or forearm.

• Lymphangitis, regional lymphadenopathy, fever; signs of septic arthritis, tenosynovitis (pain on passive extension of the finger, flexed posture, fusiform swelling) and osteomyelitis.
• Differential diagnosis: non infected puncture wound, cellulitis from other cause, cat scratch disease (papule then lymphadenopathy over 1 to 3 weeks), septic arthritis, gout, foreign body (tooth fragment), erysipelas, tularaemia.
• Complications: abscess, tenosynovitis, septic arthritis, osteomyelitis, bacteraemia and sepsis, endocarditis, meningitis, necrotising fasciitis, rabies, tetanus.

Clinical, with cultures when infected.

• Wound swab or aspirate for aerobic and anaerobic cultures; blood cultures if febrile.
• Plain radiograph for retained tooth, gas, fracture or osteomyelitis; ultrasound or MRI for deep collections and tenosynovitis.
• Cat scratch disease: Bartonella serology or PCR.

Irrigate, debride, give antibiotics and attend to tetanus and rabies.

• Supportive: copious irrigation with at least 250 to 500 mL of normal saline or tap water, debridement of devitalised tissue, leave puncture wounds open and do not suture, elevate and splint the hand, analgesia, tetanus toxoid 0.5 mL IM if vaccination is out of date (add tetanus immunoglobulin 250 units IM for dirty wounds when unvaccinated).
• Pharmacological: prophylaxis for 3 to 5 days in high risk wounds (hand, deep puncture, delayed presentation, immunocompromised): amoxicillin clavulanate 625 mg three times daily (children 25 mg/kg/day of the amoxicillin component in three doses). Established infection: amoxicillin clavulanate 625 mg three times daily for 7 to 14 days. Severe infection: ampicillin sulbactam 3 g IV every 6 hours, or ceftriaxone 2 g IV daily with metronidazole 500 mg IV every 8 hours. Penicillin allergy: doxycycline 100 mg twice daily with metronidazole 400 mg three times daily, or ciprofloxacin 500 mg twice daily with clindamycin 300 mg three times daily (not in pregnancy or children). Rabies post exposure prophylaxis: wash wound with soap and water for 15 minutes; human rabies immunoglobulin 20 IU/kg, infiltrated around the wound with the remainder IM; vaccine intradermal 0.1 mL at two sites on days 0, 3 and 7, or intramuscular 1 mL on days 0, 3, 7 and 14. Cat scratch disease: azithromycin 500 mg then 250 mg daily for 4 days.
• Procedures: surgical washout of joint or tendon sheath; drainage of abscess; debridement of bone.
• Special groups: pregnancy, amoxicillin clavulanate (avoid doxycycline and quinolones); children, weight based dosing and check of tetanus status; asplenia and immunosuppression, treat early with IV antibiotics; diabetes, low threshold for admission.
• Red flags: tenosynovitis, joint swelling, spreading erythema, fever, rapidly progressive pain, bite over a joint or tendon, hand function loss, signs of sepsis.
• Follow-up: review at 24 to 48 hours; complete rabies vaccine series; reassess for deep infection if not improving.