Presenting Signs and Symptoms

A thorough history should be obtained (Fig. 138.1), including the timing of the bite incident, the circumstances surrounding the bite, and whether a report was filed with animal control officials. If the victim knows the animal, it may be possible to ascertain the immunization status of the bite source and whether the animal is going to be quarantined to observe for signs of rabies. This information is especially important if the bite was unprovoked, if the animal was acting abnormally, or if the bite was caused by a wild animal. The patient’s medical history (including a history of allergies, current medications, and immunization status) should also be obtained.

Fig. 138.1 Algorithm for the management of human, cat, and dog bites.

HIV, Human immunodeficiency virus; IV, intravenous.

Patients with human bites, especially clenched-fist injuries, may not be forthcoming about how their injury occurred. If the wound is on the extensor surface of the metacarpophalangeal joint, the patient should be treated as though the wound is a human bite. In patients with human bites, it is important to ascertain the human immunodeficiency virus (HIV) and hepatitis status of both the patient and the attacker.

In major cases in which a patient suffers extensive injury, resuscitation from traumatic injury may be needed. Injury to deep structures, including major organs, and extensive blood loss are possible. It is usually apparent that a large animal has attacked the victim, but injuries from falls or other associated trauma can occasionally be occult. Disciplined, thorough evaluation of the patient’s physical condition is warranted when associated injury may have occurred, especially since bite wounds draw the clinician’s attention.

Differential Diagnosis and Medical Decision Making

Vital signs should be determined in all patients with bites because hypotension or tachycardia may be a sign of blood loss and fever may be a sign of infection. All bites mandate a full neurovascular examination, including a thorough motor and sensory examination distal to the bite, as well as evaluation of all the tendons and ligaments in the region of the bite. The physical examination should also include a thorough vascular examination and evaluation of any compartments involved.

Treatment

All bite wounds should undergo high-pressure irrigation of the wound with normal saline, dilute (<1%) povidone-iodine solution, or poloxamer 188 (Shur-Clens) (Table 138.2). Recent studies have looked at the efficacy of tap water as an irrigation solution^2,7; however, because no conclusive data exist at present for bite wounds, use of tap water as an irrigation solution for bite wounds cannot be supported at this time. Patients with larger or more complicated wounds may need to be anesthetized with lidocaine, bupivacaine, or another anesthetic agent before irrigation and exploration of the wound. Epinephrine should be avoided if the bite involves the fingers, toes, nose, ears, or penis.²

All wounds should be explored for foreign bodies and injuries to deeper structures such as arteries, nerves, tendons, and ligaments. All tendons in the injured area should be isolated and tested through their full range of motion to assess for partial lacerations or tears, especially if the hands or feet are involved. Any devitalized tissue or ragged edges should be débrided.

There is no clear evidence whether suturing bite wounds increases the risk for infection, nor are there conclusive data on which wounds can safely be sutured. The safest course of action is to leave most bite wounds open and have the patient return for delayed primary closure if the wound does not become infected; however, primary closure may be necessary for cosmetic or functional reasons.

Recent studies show that the infection rate of sutured bite wounds may initially be lower in certain circumstances than historically predicted. Primary closure may be safe for simple bite wounds less than 6 hours old that involve the trunk and extremities (with the exception of the hands and feet) and for simple bite wounds involving the face and neck that are less than 12 hours old.^1,2

The emergency physician should leave wounds open or consider closure by secondary intention for all infected wounds and all wounds at increased risk for infection, such as puncture wounds, hand and foot wounds, clenched-fist injuries, full-thickness wounds, wounds requiring débridement, wounds in patients older than 50 years or immunocompromised patients, wounds more than 12 hours old, and wounds involving damage to deep structures such as bones, joints, tendons, nerves, and blood vessels. Extremity wounds should be splinted and elevated.²

All patients sustaining mammalian (cat, dog, human, primate) bites should be given a dose of tetanus immune globulin and a dose of tetanus toxoid if they have never had the tetanus vaccine series or if they have not had three doses of tetanus toxoid. Patients who have had a full course of the tetanus vaccine series should be given a tetanus toxoid booster of 0.5 mg intramuscularly if more than 5 years has elapsed since the previous tetanus booster.

Patients who sustain dog, cat, or other animal bites should be evaluated for the potential need for rabies vaccination (see Chapter 179). Patients who sustain high-risk bites in which the animal cannot be quarantined should receive 20 IU/kg of human rabies immunoglobulin (HRIG) injected around the bite site or intramuscularly (or both) and 1 mL of rabies vaccine administered intramuscularly either in the deltoid in adults or in the thigh in children on days 0, 3, 7, 14, and 28. HRIG and rabies vaccine should be injected at separate sites if both are administered intramuscularly.⁸

Transmission of HIV and hepatitis B and C virus in human bites has been reported.⁹ Patients who sustain human bites need to be evaluated and counseled about HIV and hepatitis B postexposure prophylaxis (PEP) (PEP for hepatitis C does not exist). HIV PEP should be started as soon as possible within the first 48 to 72 hours after a high-risk bite and continued for 28 days. High-risk bites are those in which the assailant is known to be HIV or hepatitis positive (or both) and bites in which blood exposure is involved. Hepatitis B PEP should include hepatitis B immune globulin (HBIG) and hepatitis B vaccine (HBV) if the patient has not previously been immunized. If the patient had previously received the hepatitis B vaccination series, a titer for anti-HBV should be drawn. If the patient has hepatitis B antibodies, no treatment is needed; if there are insufficient antibodies (anti-HBV < 10 mIU/mL), the patient needs HBIG and an HBV booster.⁹

Clinical evidence is limited on which cat and dog bites should receive prophylactic antibiotics. Cat bites—especially puncture wounds, wounds involving the hand and feet, wounds involving deeper structures, wounds in immunocompromised patients, and wounds closed primarily—are considered high-risk bites, and the patient should receive prophylactic antibiotics. Prophylactic antibiotics for cat and dog bites, specifically those seen within the first 24 hours, should cover Pasteurella, Staphylococcus, Streptococcus, and anaerobic species. Options include amoxicillin-clavulanate, a second-generation cephalosporin with anaerobic activity, and penicillin plus a first-generation cephalosporin. Clindamycin plus a fluoroquinolone or trimethoprim-sulfamethoxazole may be used in penicillin-allergic patients. Doxycycline plus metronidazole can also be used in penicillin-allergic patients.

Human bites are also considered high-risk bites. Prophylactic antibiotics should be considered for bites extending through the dermis, bites closed primarily, bites with significant crush injury or requiring considerable débridement, puncture wounds, bites in elderly or immunocompromised patients, and bites that involve the hands, feet, or deeper structures. Human bite prophylaxis should cover Staphylococcus, Streptococcus, and anaerobes, including E. corrodens. Amoxicillin-clavulanate or penicillin plus dicloxacillin may be used. Clindamycin plus ciprofloxacin or trimethoprim-sulfamethoxazole may be used in penicillin-allergic patients.

Follow-Up, Next Steps in Care, and Patient Education

Wounds with significant tissue loss may need plastic surgery or hand surgery consultation for skin grafting, depending on the location of the bite. Specialty consultation is also mandated for any hand or foot wound that involves a joint, tendon, artery, or nerve. Most patients can be discharged home safely with follow-up or recheck in the ED, or both.