Human bite

Author: Kinga Ensing, 5th Year Medical Student, University of Auckland, New Zealand; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, April 2015.


Introduction

A human bite occurs as the result of human teeth penetrating skin. This can happen on purpose if someone forcibly bites down on another person’s flesh or it can happen as an accident. Human bites have a high rate of infection.

Causes of human bite

  • Violent behavior, often with alcohol
  • Domestic violence and child abuse
  • Rough play in daycare centers
  • Sporting accidents
  • Aggressive sexual play or assault
  • Thumb sucking or nail biting
  • Occupational injury to workers in the dental field
  • Seizure-related tongue injury
  • Self-inflicted wounds in those emotionally or mentally unstable1

Symptoms and signs of human bite

The area of the bite will most likely be painful and tender to touch. The bite results in a semi-circular or oval red patch and may have bruising associated with it.2

Human bite in children

Children often have bite wounds as a result of rough play. The wounds are usually located on face, upper arms and trunk. If bite mark has an inter-canine distance of 3 cm or more, consider abuse from an adult.2

Human bite in adolescents

Adolescents typically have closed fist injuries where the teeth have scratched the knuckles. These often present as small lacerations particularly over the third and fourth metacarpophalangeal joints or the proximal interphalangeal joints of the dominant hand.2

Signs of infection

Signs of infection include:1

  • Fever
  • Redness
  • Swelling
  • Tenderness
  • Purulent discharge from the wound.

Complications of human bites

Human bites have higher infection risk than animal bite wounds. This is because of the extensive bacterial flora of the human mouth and skin. One study found that in 50 patients that had an infected human bite, on average, four isolates were cultured per wound. Pathogens in human bite wounds included both aerobic and anaerobic bacteria such as:3

Complications that can arise from a bite wound infection include:1

  • Subcutaneous abscesses
  • Osteomyelitis
  • Septic arthritis and tendonitis, especially if over the knuckle area
  • Bacteraemia.

One retrospective study found that bite wounds which were greater than 3 mm or punctured had a threefold increase in infection compared to other wounds.4

Management of human bites

Wounds that have not penetrated the skin are not a cause of concern unless abuse is suspected; the resulting bruising will heal on its own.

Initial management

  • Wounds that have broken the skin surface should be stabilised.
  • Stop active bleeding by applying direct pressure.
  • Assess neurovascular function and extent of damage distal to the wound.
  • Irrigate the wound with sterile saline solution and remove visible debris
  • Tissue may require debridement.

Patients with infected bite wounds on initial evaluation need to be sent to hospital for assessment and appropriate therapy.5

Wound care for human bites

  • Swabs should be taken to aid in antibiotic management, especially if patient is at high risk of methicillin resistant Staphylococcus aureus (MRSA), eg those who have been in hospital recently, drug users, the military and so on.
  • Wounds need to be elevated to ease swelling and pain.
  • In closed fist injuries, the hand should be immobilised in a position of maximal length of ligaments.
  • Human bite wounds are generally left to heal by secondary intention, the main exception is for facial wounds which are handled by plastic surgeons.5

Antibiotics

Even if a bite wound does not look infected, prophylactic oral antibiotics for 3–5 days are recommended, especially if:

  • The bite wound occurred on the hand or close to a bone or joint
  • The bite wound was deep
  • The wound was surgically repaired
  • It was associated with a crush injury
  • It occurred in an immunocompromised patient.

If signs of infection are found on follow up, the course of antibiotics can be extended and swabs repeated.5 The agent of choice is amoxicillin-clavulanate. Alternative agents include a combination of an antibiotics with activity against Eikenella corrodens (eg doxycycline) and an antibiotic with anaerobic activity (eg metronidazole).6

Vaccination

Tetanus immune globulin and tetanus toxoid should be offered to patients with less than two primary immunisations. Those without a recent booster (last five years) can be offered the tetanus toxoid alone.5

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