Dog Bite Infection

Dog bite infection is bacterial infection of a wound inflicted by a dog's teeth, occurring in 5 to 20 percent of bites. Organisms are polymicrobial: Pasteurella canis, Staphylococcus, Streptococcus, anaerobes, and Capnocytophaga canimorsus, which can cause fulminant sepsis in asplenic or alcoholic patients.

• Children (face and head) and men are commonly bitten.
• Rabies is endemic in Kenya, transmitted mostly by domestic dogs, so every bite needs rabies assessment.

Lacerations, punctures and crush injuries; infection appears after 8 to 24 hours with erythema, pain, swelling, purulent drainage, lymphangitis and fever.

• Hands, forearms, legs in adults; face, scalp and neck in children, with risk of skull penetration.
• Differential diagnosis: non infected laceration, cellulitis from other cause, cat bite, human bite, spider bite, retained foreign body, abscess, necrotising fasciitis, septic arthritis, osteomyelitis.
• Complications: abscess, tendon and nerve damage, septic arthritis, osteomyelitis, meningitis and brain abscess (skull bite), sepsis, Capnocytophaga septic shock with purpura and gangrene, tetanus, rabies, scarring and psychological trauma.

Clinical assessment of the wound and risk.

• Wound swab (aerobic and anaerobic) from infected wounds; blood cultures if febrile; full blood count and CRP.
• Radiograph or CT for skull, hand or joint bites (fracture, tooth fragments, gas); ultrasound for abscess.
• Document the dog's vaccination status, behaviour and whether it can be observed for 10 days.

Wound care, selective antibiotic prophylaxis, tetanus and rabies prophylaxis.

• Supportive: irrigate with at least 500 mL of sterile saline under pressure, debride, leave puncture wounds and hand wounds open, close facial wounds primarily after irrigation, elevate, analgesia (paracetamol 1 g, ibuprofen 400 mg), tetanus toxoid 0.5 mL IM if immunisation is incomplete, with tetanus immunoglobulin 250 units IM for dirty wounds.
• Pharmacological: antibiotic prophylaxis for 3 to 5 days in moderate or severe wounds, hand, genital or facial bites, deep punctures, immunocompromised or asplenic patients: amoxicillin clavulanate 625 mg three times daily (children 25 mg/kg/day of amoxicillin in three doses). Infected wounds: amoxicillin clavulanate 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 (clindamycin with cotrimoxazole in children). Rabies post exposure prophylaxis for all bites by dogs of unknown or unobservable status: wash wound with soap and water for 15 minutes; human rabies immunoglobulin 20 IU/kg infiltrated into and around the wound (remainder IM at a distant site); 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 (add day 28 in immunocompromised).
• Procedures: surgical exploration and repair of tendon, nerve or vascular injury; drainage of abscess; neurosurgical care for skull penetration.
• Special groups: pregnancy, amoxicillin clavulanate and rabies vaccine are safe; children, weight based dosing and early admission for facial bites; asplenia or alcohol dependence, urgent IV antibiotics for suspected Capnocytophaga; HIV, complete the vaccine schedule and check antibody response.
• Red flags: rapidly spreading redness, hand function loss, joint involvement, fever, purpura, skull penetration, no known dog vaccination.
• Follow-up: review at 24 to 48 hours; complete rabies vaccine schedule; monitor the dog for 10 days where possible; psychological support for children.