Human Bites

Etiology

Unlike other animal bites, human bites are commonly acquired as a closed-fist injury where one individual punches another in the face and lacerates their hand on the other’s teeth. Occlusion bites have the same risk profile as closed-fist injuries but are more easily recognized and have less prevalence of skin penetration over areas with structures directly below the skin. [3]

Epidemiology

Human bites represent about 3% of the total bite injuries seen in the emergency department and are most commonly closed-fist injuries.  Bites in children are most often occlusion bites to the face and upper body from rough playing, while bites in the other age ranges are commonly at the metacarpal-phalangeal joint from striking another individual in the face or contact with another person’s teeth. These wounds are most typically found on the third, fourth, and fifth fingers at the MCP-joint. Occlusion bites predominate in presentation though this distribution may be skewed due to occlusion bites presenting as a known bite while closed-fist injuries (fight bites) typically present under altercation, assault, or other complaints that do not lend themselves to data collection and may only be incidentally found amongst other injuries. Fight bites are most commonly found in the teenage to young adult males. [4]

Pathophysiology

The physical trauma from a human bite is rarely spectacular with relatively minor lacerations and occlusion bruising being the main initial findings.  Human oral flora and contagious disease spread to account for the greater amount of morbidity with human bites. Eikenella corrodens, as well as more common aerobic and anaerobic bacteria, are normal human flora.  Herpes, hepatitis, and human immunodeficiency viruses are all transmissible through bite injuries.  Closed-fist injuries show a predication for infection due to the injury overlying the joint capsule of the MCP and the extensor tendon sheath. Direct joint and tendon sheath inoculation after the fist is relaxed allow bacteria deep penetration to normally sterile anaerobic environments.  Local infection, disseminated infection, tenosynovitis, and septic arthritis are all possible complications from human bite wounds.  

History and Physical

Focused H&P should determine the circumstances surrounding the bite, location of the bite, whether the bite was contaminated with blood, the infectious state of both individuals involved, time since the occurrence, whether the patient has been febrile, local erythema, swelling, warmth, or purulent drainage from the bite site.  Careful examination and measurement of occlusion bites in children are important as any bite with an intra-canine distance great than 3cm most likely came from an adult and should raise suspicion of abuse.  Any patient arriving after or due to an altercation should have his or her hands examined for possible fight bites.  Conversely, anyone with lacerations on their hands, or especially over the MCP joint should be questioned about the source of the injuries and educated on the danger of not having human bites treated as some patients are apprehensive to admit to the altercation.  Immunization status of the person with an injury is important in cases where transmission of disease is a concern. 

Evaluation

Wounds that were recently acquired are usually minor, less than 2cm long, and rather superficial which makes them easy to overlook or dismiss especially in light of other injuries or complaints. Contaminated or otherwise obscured skin on hands should be cleaned thoroughly to evaluate for a possible fight bite especially in intoxicated individuals who cannot provide a reliable history.  Infected joints or tendon sheaths are more apparent but also warrant surgical consultation and IV antibiotics. If a bite in a child is suspicious for abuse a thorough exam should be performed, a broadened history should be taken, and CPS should be contacted.[1][3]

Treatment / Management

All wounds should be extensively irrigated and the patient’s tetanus status updated if necessary.  Provide appropriate pain management before exploration, irrigation, or debridement of the wounds.  All human bite wounds that pierce the skin should receive amoxicillin-clavulanate prophylaxis for a week, and the patient is given strict wound care precautions.  The patient's TDaP status should be updated if necessary.  Any laceration to the MCP-joint is a closed-fist injury until proven otherwise.  If signs or symptoms of infection in a joint space or tendon sheath are present orthopedics should be consulted for evaluation for surgical washout and inpatient treatment with IV antibiotics.  Repair of lacerations from human bites should follow the same principles as that of other bites and in most cases should be left to heal by secondary intention to prevent providing a more hospitable environment for bacteria to reproduce. [5][6]

Differential Diagnosis

• Animal bites to the head and neck

• Cellulitis

• Hand infections

• Inflammatory breast carcinoma

• Insect bites

• Paget disease

• Tetanus

• Thrombophlebitis

• Radiation fibrosis

Complications

• Cosmetic deformity
• Loss of function
• Infectious tenosynovitis
• Necrotizing fasciitis
• Abscess formation
• Amputation
• Osteomyelitis
• Septic joint