Cat bite to the hand — cellulitis

Diagnosis: Infected cat bite with early septic arthritis of the third MCP joint. Rapid erythema, warmth, tenderness with frequently purulent drainage points to Pasteurella multocida — normal dog and cat oral flora, cats sourcing 60 to 80% of cases — with septic arthritis plus osteomyelitis most commonly hitting a finger or hand after a cat bite.^[4]

Assessment:

1. History — time of bite, immune status (diabetes, immunosuppression, asplenia), tetanus status.
2. Examination — assess joint range of movement and flexor-sheath signs for tenosynovitis; document the neurovascular status distally; explore for tendon, bone, and foreign bodies.
3. X-ray the hand for a retained tooth fragment and air within the joint.
4. Swab the purulent wound for microscopy and culture; bloods if systemically unwell.^[2]

Management:

1. Copious saline irrigation and debridement of devitalised tissue; remove any foreign body. Do not close primarily.
2. Amoxicillin-clavulanate — excellent in vitro activity against common bite isolates including beta-lactamase producers; dose and duration per local protocol.
3. Tetanus prophylaxis — assess status; immunoglobulin is essential for incompletely immunised patients with dirty wounds, with boosters every 10 years.^[3]
4. Hand-surgery referral for any clenched-fist injury, joint penetration, established septic arthritis or tenosynovitis, or failure to improve on oral therapy — for washout and intravenous antibiotics.
5. Immobilise and elevate the hand; early review.

The cardinal principle: amoxicillin-clavulanate shows excellent in vitro activity against common bite isolates.^[2]