Human Bite Infection

Human bite infection follows tooth penetration of skin by a person's bite or by a clenched fist striking a mouth (fight bite). The human oral flora is polymicrobial: Streptococcus viridans, Staphylococcus aureus, Eikenella corrodens, Fusobacterium, Prevotella and Peptostreptococcus.

• Clenched fist injuries over the metacarpophalangeal joint are the most dangerous.
• Bites also transmit viruses, including hepatitis B, hepatitis C and, rarely, HIV.

Crescent shaped tooth marks or small laceration over the knuckle, with pain, swelling, erythema, purulent discharge and reduced finger movement; patients often delay presentation.

• Extensor tendon, joint capsule and metacarpal head injury under a small wound; pain on finger movement suggests joint penetration.
• Differential diagnosis: cellulitis from another cause, abscess, septic arthritis, gout, herpetic whitlow, osteomyelitis, flexor tenosynovitis, foreign body (tooth fragment).
• Complications: septic arthritis, tendon sheath infection, osteomyelitis, abscess, necrotising infection, sepsis, permanent loss of hand function, transmission of hepatitis B, hepatitis C and HIV, tetanus.

Clinical, with imaging.

• Radiograph of the hand for fracture, tooth fragment or air in the joint; ultrasound or MRI for deep infection.
• Wound culture (aerobic and anaerobic); blood cultures if febrile; full blood count, CRP.
• Test the patient (and the biter where consent is possible) for HIV, hepatitis B and hepatitis C.

Treat all significant bites with antibiotics and early drainage.

• Supportive: irrigate with at least 500 mL of saline, debride, leave the wound open without suturing, splint and elevate the hand, analgesia (paracetamol 1 g, ibuprofen 400 mg), tetanus toxoid 0.5 mL IM if vaccination is out of date; hepatitis B vaccine, and hepatitis B immunoglobulin 500 IU IM if the biter is hepatitis B positive and the victim is not immune; counselling and baseline serology.
• Pharmacological: amoxicillin clavulanate 625 mg three times daily for 3 to 5 days as prophylaxis; 7 to 14 days (and 2 to 4 weeks for joint or bone infection) for established infection. Severe infection or fight bite: ampicillin sulbactam 3 g IV every 6 hours, or ceftriaxone 2 g IV daily with metronidazole 500 mg IV every 8 hours. Eikenella is resistant to clindamycin, macrolides and metronidazole alone; in penicillin allergy give doxycycline 100 mg twice daily or ciprofloxacin 500 mg twice daily combined with metronidazole 400 mg three times daily. HIV post exposure prophylaxis, if the biter is HIV positive or status unknown with blood exposure and broken skin: tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg daily for 28 days, started within 72 hours.
• Procedures: surgical washout of the joint or tendon sheath, debridement of devitalised tissue, drainage of abscess; exploration of fight bites in the operating theatre.
• Special groups: pregnancy, amoxicillin clavulanate and the antiretroviral post exposure regimen of tenofovir, lamivudine and dolutegravir; children, weight based dosing and consider non accidental injury or abuse; diabetes and immunosuppression, admit for IV antibiotics; adult victims of assault, forensic documentation and support.
• Red flags: pain on movement of a finger, fight bite over a joint, tendon exposure, spreading cellulitis, fever, delayed presentation, signs of necrotising infection.
• Follow-up: review at 24 hours and 48 hours; repeat HIV, hepatitis B and hepatitis C tests at 6 weeks, 3 months and 6 months; complete vaccination.