(See also Spirochetes: Rat-Bite Fever.)

Human and other mammal (mostly dog and cat, but also squirrel, gerbil, rabbit, guinea pig, and monkey) bites are common and occasionally cause significant morbidity and disability. The hands, extremities, and face are most frequently affected, although human bites can occasionally involve breasts and genitals.

Bites by large animals sometimes cause significant tissue trauma; about 10 to 20 people, mostly children, die from dog bites each year. However, most bites involve relatively minor wounds.

Infection

In addition to tissue trauma, infection from the biting organism's oral flora is a major concern. Human bites can theoretically transmit viral hepatitis and HIV. However, HIV transmission is unlikely because the concentration of HIV in saliva is much lower than in blood and salivary inhibitors render the virus ineffective.

Rabies is a risk with certain mammal bites (see Brain Infections: Rabies). Monkey bites, usually restricted in the US to animal laboratory workers, carry a small risk of herpesvirus simiae infection, which causes vesicular skin lesions at the inoculation site and can progress to encephalitis, which is often fatal.

Bites to the hand (see also Hand Disorders: Infected Bite Wounds) carry a higher risk of infection, specifically cellulitis, tenosynovitis, septic arthritis, and osteomyelitis, than other bite sites; this higher risk is a particular concern in human bites resulting from a clenched-fist strike to the mouth (fight bite), the most common human bite wound. In fight bites, the skin wound moves away from the underlying damaged structures when the hand is opened, trapping bacteria inside, and patients often delay seeking treatment, allowing bacteria to multiply. Human bites to sites other than the hand have not been proved to carry a greater risk of infection than bites from other mammals. Cat bites to the hand also have a high risk of infection because cats' long, slender teeth often penetrate deep structures, such as joints and tendons, and the small punctures are then sealed off.

Diagnosis

• Evaluation in the position in which the bite was inflicted
• Assessment for damage to underlying nerve, tendon, bone, and vasculature and for presence of foreign bodies

Human bites sustained in an altercation are often attributed to other causes to avoid involvement of the authorities or to ensure insurance coverage. Domestic violence is often denied.

Wounds are evaluated for damage to underlying structures (eg, nerves, vasculature, tendons, bone) and for foreign bodies (see Lacerations: Evaluation). Evaluation should focus on careful assessment of function and the extent of the bite. Wounds over or near joints should be examined in the position in which they were inflicted (eg, with fist clenched) and explored under sterile conditions to assess tendon, bone, and joint involvement and to detect retained foreign bodies. Wounds inflicted by chomping may appear to be minor abrasions but should be examined to rule out deep injury.

Culturing fresh wounds is not valuable for targeting antimicrobial therapy, but infected wounds should be cultured. For patients with human bites, screening for hepatitis or HIV is recommended only if the attacker is known or suspected to be seropositive.

Treatment

• Meticulous wound care
• Selective wound closure
• Selective use of prophylactic antibiotics

Hospitalization is indicated if complications mandate very close monitoring, particularly when patient characteristics predict a high risk of nonadherence with outpatient follow-up. Hospitalization should be considered in the following circumstances:

• When a human bite is infected (including clenched-fist injuries)
• When a nonhuman bite is moderately or severely infected
• When loss of function is evident
• When the wound threatens or has damaged deep structures
• When a wound is disabling or difficult to care for at home (eg, significant wounds to both hands or both feet, hand wounds that require continuous elevation)

Priorities of treatment include wound cleaning, debridement, closure, and infection prophylaxis.

Wound care

Wounds should first be cleaned with a mild antibacterial soap and water (tap water is sufficient), then pressure irrigated with copious volumes of saline solution using a syringe and IV catheter. A dilute povidone-iodine solution (10:1 with 0.9% saline) may also be used. A local anesthetic should be used as needed. Dead and devitalized tissue should be debrided.

Wound closure is done only for select wounds. Many wounds should initially be left open, including the following:

• Puncture wounds
• Wounds to the hands, feet, perineum, or genitals
• Wounds more than several hours old
• Wounds that are heavily contaminated
• Wounds that are markedly edematous
• Wounds that show signs of inflammation
• Wounds that involve deeper structures (eg, tendon, cartilage, bone)
• Wounds from human bites
• Wounds sustained in a contaminated environment (eg, marine, field, sewers)

In addition, wound resolution in immunocompromised patients may be better with delayed closure. Other wounds (ie, fresh, cutaneous lacerations) can usually be closed after appropriate wound hygiene. Results with delayed primary closure are comparable to those with primary closure, so little is lost by leaving the wound open initially if there is any question.

Hand bites should be wrapped in sterile gauze, splinted in position of function (slight wrist extension, metacarpophalangeal and both interphalangeal joints in flexion). If wounds are moderate or severe, the hand should be continuously elevated (eg, hanging from a pole).

Facial bites may require reconstructive surgery given the cosmetic sensitivity of the area and the potential for scarring.

Infected wounds may require debridement, suture removal, soaking, splinting, elevation, and IV antibiotics, depending on the specific infection and clinical scenario. Joint infections and osteomyelitis may require prolonged IV antibiotic therapy and orthopedic consultation.

Antimicrobials

Thorough wound cleaning is the most effective and essential way to prevent infection and often suffices. There is no consensus on indications for prophylactic antibiotics. Studies have not confirmed a definite benefit, and widespread use of prophylactic antibiotics has the potential to select resistant organisms. Drugs do not prevent infection in heavily contaminated or inadequately cleaned wounds. However, many practitioners prescribe prophylactic antibiotics for bites to the hand and some other bites (eg, cat bites, monkey bites).

Infections are treated with antimicrobials initially chosen based on animal species. Culture results, when available, guide subsequent therapy.

• Human and dog bites: For outpatients, the preferred drug is amoxicillin/clavulanate 500 to 875 mg po bid for 3 days for prophylaxis or 5 to 7 days for treatment. Ampicillin/sulbactam 1.5 to 3.0 g IV q 6 h is a reasonable empiric choice for inpatients; it covers α-hemolytic streptococci, Staphylococcus aureus , and Eikenella corrodens, the organisms most commonly cultured from human bites, and Pasteurella species (P. canis and P. multocida) and Capnocytophaga canimorsus present in dog bites. Penicillin-allergic patients with human bites can be treated with trimethoprim/sulfamethoxazole 160/800 mg IV q 12 h plus clindamycin 150 to 300 mg IV q 6 h. For penicillin-allergic patients with infected dog bites, doxycycline is an acceptable alternative, except for children > 8 yr and pregnant women. Erythromycin can be used, but the risk of treatment failure is higher because of antimicrobial resistance. Other acceptable combinations include clindamycin and a fluoroquinolone for adults or clindamycin and trimethoprim/sulfamethoxazole for children.
• Cat bites: A fluoroquinolone (eg, ciprofloxacin 500 mg po bid for 5 to 7 days) for prophylaxis and treatment is recommended because of the prevalence of P. multocida. (Bartonella henselae is also transmitted by cat bites—see Gram-Negative Bacilli: Cat-Scratch Disease) Alternatives for penicillin-allergic patients are clarithromycin 500 mg po bid for 7 to 10 days or clindamycin 150 to 300 mg po qid for 7 to 10 days.
• Squirrel, gerbil, rabbit, and guinea pig bites: These bites rarely become infected, but when they do, they can be treated with the same drugs as infected cat bites.
• Monkey bites: Monkey bites should be treated prophylactically with IV acyclovir 800 mg 5 times/day for 14 days.

Patients with human bites should receive postexposure prophylaxis for viral hepatitis (see Hepatitis: Prevention) and HIV (see Human Immunodeficiency Virus (HIV): Postexposure prophylaxis (PEP)) as indicated by patient and attacker serostatus. If status is unknown, prophylaxis is not indicated.

Last full review/revision February 2009 by Robert Barish, MD