Human Bites in Emergency Medicine

Pathophysiology

In a closed-fist injury, forces sufficient to break the skin from striking an opponent's tooth often inoculate the extensor tendon and its sheath. As the hand is flexed at the time of impact, the bacterial load is transferred caudally when the hand is opened and the tendon slides back to its relaxed state. Resulting contamination cannot be removed readily through normal cleansing and irrigation.

When a finger is bitten, such as in a chomping-type injury, tendons and their overlying sheaths are in close proximity to the skin. The wound may appear to be a minor abrasion-type injury, but careful inspection is required to rule out deep injury.

When a tooth strikes the head, even a deep puncture wound may appear innocuous. Deep, subgaleal, bacterial contamination is possible. This is especially true in young children who have relatively thin soft scalp and forehead tissue.

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Epidemiology

Frequency

United States

Exact incidence of human bite wounds is unknown, and many cases do not come to medical attention. Institutionalized patients with poor impulse control create a high-risk environment for human bite wounds. Lesch-Nyhan syndrome is an uncommon disorder that includes self-mutilation through biting.

International

In a 4-year retrospective review in the United Kingdom, 421 (13%) human bites were identified out of 3136 case notes. The majority of those bitten were young males, with 44% of the males aged 16-25 years. The male-to-female ratio was 3:1.^[1]

Mortality/Morbidity

The primary concern with human bites of the hand is infection, which can be severe because of spread along tendon sheaths and deep into the hand. Surgical incision and drainage may be needed. Resultant scarring and tissue damage may compromise normal function of the hand.
Infection also is the major complication of bites in other areas of the body. Most can be treated adequately; however, infections of poorly vascularized structures, such as ear cartilage, may be difficult to treat.
Other serious infectious complications such as osteomyelitis of the skull vault, necrotizing fasciitis, infectious tenosynovitis, and septic arthritis have been associated with human bites. Transmission of human immunodeficiency virus (HIV) has been reported as a result of a human bite wound.^[2]

Sex

Males generally are at higher risk than females for bite wounds due to their typically more aggressive nature. Closed-fist injuries are encountered almost exclusively in young males.

Age

Closed-fist injuries occur most often in adolescents and adults younger than 40 years.
Toddlers frequently bite one another, but injuries usually are superficial and low risk.
Penetrating tooth injuries of the scalp and forehead pose a higher risk to young patients than to older patients.

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History

Consider all injuries dorsal to the metacarpophalangeal (MCP) joint bite wounds until proven otherwise. Explanations offered for such wounds often are misleading, thus extreme caution is necessary. While a careful explanation of the need for an accurate history may elicit the truth from the patient, experienced emergency physicians often treat such injuries as bites regardless of the history.
Most bite wound infections are present at the initial ED visit. With closed-fist injuries, the initial injury often appears minor to the patient, thus no care is sought until infection develops. If a child receives a small laceration to the scalp or forehead during unwitnessed horseplay, carefully ascertain whether a tooth caused the wound to minimize complications.
Other aspects of a patient's history that may influence care include tetanus immunization status, time delay from injury to presentation, disability encountered, and the presence of underlying immunosuppressive disease.

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Physical

Physicians must be wary of any laceration overlying the MCP joint. Additionally, carefully assess bite wounds of the fingers for deeper penetration into the tendon apparatus. Extending the wound may be necessary to fully evaluate the underlying structures and the extent of injury.
The following points should be noted for specific bite wounds:
- MCP wounds (closed-fist injury) - Integrity of the extensor tendons, signs of infection, crepitation, loss of knuckle height
- Chomping injuries of the finger - Integrity of the extensor and flexor tendons, evidence of infection including flexor tenosynovitis
- Ear bites - Loss of tissue, violation of cartilage
- Other bites - Tissue loss, depth of penetration

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Causes

As with most intentional injuries, human bites often are the result of an incident involving alcohol.
Domestic violence may be a factor.
Child abuse may be associated with bite wounds from adults.

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Laboratory Studies

Routine laboratory studies: These are generally not indicated because the injured population is usually young and healthy. Diagnosis of infection is clinical.
Wound culture: Microbiology of human bite wounds is fairly consistent, yet an untreated infected bite generally is cultured if purulence is present.

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Imaging Studies

Radiography
- In closed-fist injuries, an underlying metacarpal head fracture is possible. This may dictate inpatient treatment.
- Infected bites of the hand of some duration may have evidence of osteomyelitis on plain radiographs.
- If history indicates that a tooth was broken during the incident, a radiograph may be indicated to examine for a foreign body.

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Procedures

Wound care

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Prehospital Care

Recovery of avulsed tissue parts (eg, ear, finger) is an important consideration for prehospital providers. Otherwise, human bite wound management generally is uncomplicated and involves temporary dressing and transport.
Avulsed parts should be wrapped in sterile gauze dressing that is soaked with normal saline and placed in a plastic bag that is, in turn, placed in a container of ice water.

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Emergency Department Care

The acute, noninfected human bite

Cleanse and debride as usual
Tetanus prophylaxis as indicated
Antibiotic prophylaxis
- The literature regarding prophylaxis of human bite wounds is sparse. Only 2 randomized controlled trials directly address the question. In the first, patients with acute, noninfected human bites to the hand were randomized to prophylaxis with placebo, an oral cephalosporin, or a parenteral cephalosporin plus penicillin. Bites involving joints or tendons were excluded from this study. The results were dramatic, with 47% of the placebo group developing infection, while none of the subjects treated with antibiotics developed infection.^[3]
- A larger, more recent trial attempted to address the question in patients with "low-risk" human bites by randomizing them to placebo or an oral cephalosporin plus penicillin. This trial excluded patients with bites to the hands, feet, or cartilaginous structures, and no patient in this trial had a bite wound that penetrated deep to the epidermis. In this trial, no statistically significant difference was found in the placebo group compared to the group treated with antibiotics.^[4]
- A large retrospective series examining human bite wounds in children found that none of the bites manifesting as abrasions became infected, while the rate of infection was much higher in bite wounds that caused punctures or lacerations.^[5]
- From these data one can draw several conclusions:
  1. Acute human bites that do not penetrate the epidermal layer probably do not need antibiotic prophylaxis as long as they do not involve the hands, feet, joints, or cartilaginous structures.
  2. Human bites that completely penetrate the epidermal layer, as well as bites that involve joints or cartilaginous structures probably merit antibiotic prophylaxis, but the evidence is not strong.
  3. Human bites to the hand are at high risk for infection and probably should be given antibiotic prophylaxis.
Injury patterns
- Closed-fist injuries: An underlying fracture dictates inpatient treatment under certain circumstances. After appropriate anesthesia, explore the wound for joint space violation or tendon injury. Involvement of the joint space indicates admission. Consider patients with tendon injuries, which usually are present, for admission. Proper wound assessment includes using a tourniquet and extending the wound as needed to improve visualization. Provide outpatient treatment of these wounds (careful wound cleansing, antibiotic coverage, bulky dressing or splint, elevation) only in consultation with hand or orthopedic service. Early, mandatory follow-up care is essential.
- Chomping injuries: Treat noninfected wounds that appear to violate the tendon apparatus in the same manner as noninfected closed-fist injuries.
- Puncture wounds: These most commonly are encountered about the head. Such wounds are difficult to clean adequately unless extended to allow for effective irrigation. Even in the absence of infection, such wounds are best left open and closed secondarily, if cosmetically necessary.
- Bites to the ear or nose: When associated with tissue loss, these wounds require consultation with plastic surgery or ear, nose, and throat (ENT) service. Seeking consult for a bite that violates cartilage in these areas also is prudent because of poor blood supply to cartilage and difficulties in treating chondritis.

The infected human bite wound

The current recommendations from the Infectious Disease Society of America (IDSA) call for the use of amoxicillin/clavulanate or ampicillin/sulbactam. Cephalexin, which is commonly used for skin and soft-tissue infections, is ineffective against Eikenella corrodens, an important pathogen in infected human bites. TMP/SMX plus clindamycin is an acceptable alternative in the penicillin-allergic patient.^[6]
Infected closed-fist injuries are a special case because of the deep nature of these infections and relatively poor vascular supply to the tendons and other connective tissue. Admitting patients for intravenous (IV) antibiotic therapy is generally considered appropriate is these cases. Surgical debridement and drainage also may be necessary.

Other considerations

HIV transmission has been noted only rarely after a human bite. Exposure to saliva alone is not considered a risk factor for HIV (or hepatitis) transmission. Transmission requires HIV-infected blood mixed in the saliva of the biter and a skin break on the victim. The reverse consideration also is important in that blood drawn from an HIV-infected victim would come in contact with the mucous membranes of the biter. A 2005 Centers for Disease Control and Prevention recommendation states that postexposure prophylaxis with a 28-day course of highly active antiretroviral therapy (HAART) should be used in either of these 2 scenarios.^[7]

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Consultations

In general, consult hand and/or orthopedic service for infected human bites of the hand and those involving a fracture, joint space violation, or significant tendon injury. Consider consultation or agreed-upon protocols for other human bites to the hand.
Consult plastic surgery or ENT service for significant injuries to the special structures about the face and for wounds involving significant tissue loss.

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Medication Summary

The only drug therapy of significance in human bites is antibiotic treatment. Bacterial flora include that of the mouth and skin. Theoretically, penicillin treats oral pathogens and may suffice for prophylactic treatment as Staphylococcus species probably only infect bite wounds secondarily.

Once a human bite is infected, beta-lactamase–producing staphylococci must be addressed. Eikenella corrodens may not be covered by first-generation cephalosporins. Additionally, Eikenella species are resistant to clindamycin, penicillinase-resistant semisynthetic penicillins, and metronidazole. A broad-spectrum antibiotic, rather than combination therapy, is the usual choice for infected bite wounds. An in vitro study of 50 infected human bites by Talan et al indicated that amoxicillin-clavulanic acid and moxifloxacin demonstrated excellent activity against common isolates.^[8]

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Amoxicillin/clavulanate (Augmentin)

Dosing, Interactions, etc.

Clinical Context: Drug combination that extends antibiotic spectrum of this penicillin to include bacteria normally resistant to beta-lactam antibiotics. DOC for noninfected human bite wounds. Dosing is based on amoxicillin component. Indicated for skin and skin structure infections caused by beta-lactamase-producing strains of Staphylococcus aureus.

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Ampicillin/sulbactam sodium (Unasyn)

Dosing, Interactions, etc.

Clinical Context: Drug combination that uses beta-lactamase inhibitor with ampicillin; covers skin, enteric flora, and anaerobes. DOC for infected bites.

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Cefoxitin (Mefoxin)

Dosing, Interactions, etc.

Clinical Context: Alternative drug for infected bites; second-generation cephalosporin indicated for management of infections caused by susceptible gram-positive cocci and gram-negative rods. Many infections that are caused by gram-negative bacteria and are resistant to some cephalosporins and penicillins respond to cefoxitin.

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Moxifloxacin (Avelox)

Dosing, Interactions, etc.

Clinical Context: Inhibits the A subunits of DNA gyrase, resulting in inhibition of bacterial DNA replication and transcription.

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Class Summary

Therapy must cover all likely pathogens in the context of the clinical setting.

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Tetanus immune globulin (TIG)

Dosing, Interactions, etc.

Clinical Context: Used for passive immunization of any person with a wound that may be contaminated with tetanus spores.

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Class Summary

These agents are used to immunize patients against tetanus.

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Further Outpatient Care

Patients discharged from the ED with human bite wounds more significant than superficial abrasions should have early, mandatory follow-up care within 1-2 days.

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Complications

Infection and resulting sequelae are the main complications in human bites. These include serious soft tissue infection, tendon damage, tissue contracture, and osteomyelitis.
Cosmetic deformity may be a complication.

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Prognosis

The prognosis is generally excellent, except for possible sequelae from serious infection.

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Author

Jeffrey Barrett, MD, Assistant Professor, Department of Emergency Medicine, Temple University School of Medicine