Key Practice Points
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All animal bites exhibit similarities, but there are enough differences that each one needs to be evaluated and managed individually.
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The most important steps in bite wound management are cleansing, irrigation, and débridement of devitalized tissue. Dilute povidone-iodine solution (not the scrub preparation) is used for cleansing and irrigation, because it is both bactericidal and virucidal.
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Puncture wounds, especially those caused by cats, have a high risk of seeding deep tissue with bacteria and causing infection with Pasteurella multocida. It is important to open those wounds for thorough irrigation.
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Dog bites, which are the most common mammalian bite, have the least virulent bacteria and the lowest infection rate. Cat and human bites have more virulent bacteria with a higher infection rate.
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All of the important bacteria of dog, cat, and human bites are susceptible to ampicillin/clavulanate. For patients allergic to penicillin-based antibiotics, other choices are effective for prophylaxis or for treating established infections, and these antibiotics are listed in the text.
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Because suture material is a foreign body, suturing mammalian bite wounds is not recommended except for cosmetic concerns such as bite wounds on the face. Proper and vigorous local wound care will likely protect a sutured wound from becoming infected.
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Clenched-fist human injuries (striking human teeth) are very likely to penetrate tendon and metacarpophalangeal joints. These wounds often require the advice of a consultant for exploration and irrigation of the wound, tendon, and joint.
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Since 2000, no cases of human rabies have been contracted from domestic animals. The most common cause of human rabies is from bats. No human has contracted rabies from a properly immunized animal.
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Wound care and local injection of rabies immune globulin, as soon as possible after the bite occurs, are the key steps for rabies prevention.
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Optimal timing of postexposure prophylaxis is 48 hours from the bite occurs. However, because the average rabies incubation period is 30 to 90 days, up to 2 years’ postexposure prophylaxis should never be denied the patient. Local public health officials and the Centers for Disease Control and Prevention (CDC) can assist in complicated cases.
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Recent recommendations in postexposure rabies prophylaxis from the CDC have reduced the number of postexposure human diploid cell vaccine (HDCV) injections from 5 to 4.
Animal and human bites are common wounds managed by emergency caregivers. Bites can be from a multitude of sources, but most are caused by dogs, cats, and humans. Despite apparently similar mechanisms of injury, each type of bite has different clinical, microbiologic, and treatment considerations that affect the management of bite wound patients. With animal bites, there is also the possibility of secondary systemic infectious complications, the most important of which is rabies. It is the responsibility of any person caring for an animal bite victim to investigate thoroughly the biting circumstances and to make an appropriate decision about whether or not to administer rabies prophylaxis.
The mechanism of injury from an animal bite or attack plays an important role in predicting the chance of infection and the choice of management technique. All animal bites are to be considered contaminated with potentially pathogenic bacteria. These injuries frequently are associated with crushing, tearing, and avulsion forces and devitalized tissue. The combination of bacterial contamination with accompanying devitalized skin and fascia creates a setting ripe for the establishment of infection. The risk of infection is greater for certain circumstances listed in Box 15-1 .
Puncture or crush wounds
Bites to hands, face, and feet
Bone, joint, tendon involvement
Delayed presentation, >8 hours from bite incident
Immunocompromised or asplenic host
Wound requiring surgical repair
Presence of prosthetic appliance
General Bite Wound Management
Wound management depends on the type of wound, its severity, and its anatomic location. Simple contusions and superficial bite abrasions, in which no obvious skin puncture, laceration, or avulsion is present, can be treated by thorough cleansing alone. Despite the relatively minor appearance of many of these wounds, the patient still is at risk for developing rabies, and this possibility has to be addressed. For larger wounds that violate the epidermis and dermis, standard wound care techniques are performed as follows:
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Povidone-iodine solution (not the detergent scrub preparation) is the wound cleansing solution recommended for periphery cleansing. The standard 10% solution is diluted 10:1 to 20:1 with saline and can serve as the cleansing agent and the irrigant. Povidone-iodine is virucidal and the potential for rabies in animals and human immunodeficiency virus (HIV) in humans make it the preferred bite wound cleansing agent.
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After thorough scrubbing of the wound periphery, copious high-pressure irrigation is the next step, using a 19-G needle, catheter, or splash shield attached to a 20-mL or 35-mL syringe. Delivering diluted povidone-iodine solution directly into the wound enhances its microbicidal action.
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Débridement of all devitalized tissue and wound edges is essential for reducing the possibility of wound infection. Irrigation after débridement is recommended because it provides greater exposure of the wound. Retrospective and prospective studies have shown that wound infection is reduced significantly after débridement.
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For fang wounds, particularly slender cat teeth wounds, there is often minimal devitalization of the skin. Edge débridement might not be necessary. The problem of adequate wound cleansing remains, however. To facilitate effective irrigation, after local infiltration of anesthesia, the entry site can be widened with a simple 1- to 1.5-cm incision across the puncture with a no. 15 knife blade ( Fig. 15-1 ). The new wound is retracted open with a hemostat or forceps to permit irrigation. These incisions are left to close without sutures. If the edges are devitalized, they should be trimmed back to viable skin.
Figure 15-1
Fang wound management. A, A fang wound with a suggested line of incision to open the wound for effective irrigation and débridement. B, A small 1- to 1.5-cm incision can be made with a scalpel and a no. 15 blade. C, When incised, the wound can be exposed with forceps and can be copiously irrigated. D, The incision also facilitates wound edge débridement if devitalization or excessive contamination is present.
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Purulence or suspected infection is cultured.
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Radiographs are obtained when fracture or joint penetration is suspected.
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Proper tetanus immunization is ensured.
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The wound is covered with a nonadherent base (an antibiotic ointment is optional). The base is covered with gauze pads and tape or a gauze wrap to secure the dressing.
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Assessment and treatment for rabies exposure are performed if necessary.
Specific Injuries
The most important steps in the management of animal and human bites are cleansing, irrigation, and débridement. However, the most controversy exists over the choice of antibiotics for prophylaxis and for the treatment of established infections. Antibiotic choices listed here are based on the likely pathogenic organisms in a bite wound and the antimicrobial susceptibility of the available antibiotics. Except for amoxicillin/clavulanate, no single antibiotic covers all of the important organisms. For this reason most of the recommendations include two antibiotics to ensure broad-spectrum coverage. Coverage can always be changed based on the clinical course of the patient and available wound cultures.
Dog Bites
Microbiology and Risk for Infection
More than 80% of animal bites are dog bites. The mouths of animals, including dogs, have a bewildering number and variety of bacteria. However, only a few of those bacteria actually cause the majority of established infections. Therefore, prophylaxis should cover at least the likely infecting organisms ( Table 15-1 ). Fifty percent of bacteria recovered from infected wounds are Pasteurella canis . Other organisms include S. aureus, streptococi, Moroxella spp., and anaerobes. An unusual organism, but virulent, is Capnocytophaga canimorsus. Multiorgan failure, disseminated intravascular coagulation, and gangrene have been associated with this gram-negative bacillus, but infection most often occurs in immunosuppressed or chronically ill patients. The overall infection rate from dog bites varies from 2% to 20%. Infection is more likely to occur in patients with risk factors, as listed in Box 15-1 .
| Bite Wound | Treatment |
|---|---|
| Dog, cat, human | Adults |
| Amoxicillin/clavulanate 875/125 mg PO bid Cefuroxime 500 mg PO bid plus clindamycin 300-450 mg PO tid † TMP/SMX DS 2 tabs PO bid plus † clindamycin 300-450 mg PO tid | |
Children (1-12 yr) | |
| Amoxicillin/clavulanate 25 mg/kg (amox) PO bid Cefuroxime 15 mg/kg PO bid plus † clindamycin 7 mg/kg PO tid † TMP/SMX 4-6 mg/kg PO bid plus † clindamycin 7 mg/kg PO tid |
∗ Established infection: treat for 14 days. Prophylaxis: treat for 3-5 days.
† Includes activity against community-acquired community-associated methicillin-resistant Staphylococcus aureus .
Dog Bite Wound Management
Dog bites are managed according to the general bite wound management guidelines mentioned previously.
Dog Bite Prophylaxis
The most controversial area of dog bite management is the use of prophylactic antibiotics for wounds that appear to be noninfected. The preponderance of evidence is that antibiotics do not reduce the infection rate in low-risk dog bite wounds. Meta-analyses and systematic reviews of available controlled trials found, however, that prophylactic antibiotics were beneficial in high-risk settings. The high-risk setting for which there is the best evidence for the prophylactic effect of antibiotics is for noninfected-appearing hand wounds. Based on the potentially infecting organisms, ampicillin/clavulanate provides good coverage in this setting (see Table 15-1 ). Alternatives for penicillin-allergic patients are listed as well.
Suturing
The issue of whether to suture dog bite wounds is controversial. Investigational data and the author’s personal experience support the practice of primary suture closure of low-risk dog bite wounds. In a study by Chen, suture closure of dog bites was 94% successful compared with 97% in nonbite wounds. Caution is recommended for wounds more than 8 to 12 hours old, fang (puncture) wounds, hand lacerations, or wounds that are at high risk. When risk to closure exists, delayed primary closure (tertiary union) or open closure (secondary union) can be considered. Because of the cosmetic concerns associated with facial bites and a low potential for infection, suturing, even after 8 to 12 hours, can be considered. Consultation with a specialist is recommended to assist in the decision. Whenever primary closure of any dog bite is performed, deep closures are avoided to minimize the potential for infection.
Established Dog Bite Infection
For wounds with signs of infection (i.e., purulence, redness, heat, tenderness, and lymphangitis), the initial empirical dose of intravenous antibiotics should be broad spectrum. Ampicillin/sulbactam (Unasyn) provides coverage for the most likely infecting organisms ( Table 15-2 ). If a patient requires admission to the hospital, this agent can be continued until wound culture results are available to determine further therapy. If the patient can be treated as an outpatient, oral ampicillin/clavulanate (Augmentin) can be used after the initial parenteral ampicillin/sulbactam. Culture results can guide outpatient therapy as well. Total treatment time is approximately 14 days; however, the patient is recommended to return in 48 to 72 hours for assessment of treatment effectiveness.
| Bite Wound | Treatment |
|---|---|
| Cat, dog, human | Adults |
| Ampicillin/sulbactam 1.5-3.0 g IV q6h Ceftriaxone 1 g IV q12h plus metronidazole 500 mg q8h TMP/SMX 4-10 mg/kg (TMP) IV q12h plus clindamycin 600 mg IV q8h | |
| Children (1-12 yr) | |
| Ampicillin/sulbactam 50 mg/kg IV q12h plus clindamycin 7.5 mg/kg IV q8h TMP/SMX 2-3mg/kg IV q12h plus clindamycin 7.5 mg/kg mg IV q8h |
Cat Bites
Microbiology and Risk Factors for Infection
Cat wounds can be inflicted by both teeth and claws. In a study of infected cat bites, Pasteurella multocida was found in 75% of cases. It is important to remember that cats lick their paws, which can be covered with P. multocida . This organism is particularly virulent. Because cat teeth are long and slender, deep tissue, tendon, or joint seeding can occur. Infection is characterized by rapid onset and spreading (less than 24 hours), pain, and thin grayish discharge. Other organisms that can be cultured are aerobes, including S. aureus and streptococci, and anaerobes. Other risk factors for infection are similar to the factors listed for dog bites.
Cat Bite Wound Management
Cat bites are managed according to the general bite wound management guidelines listed previously. Because of the potential for deep penetration, it is important to open fang bites for irrigation to reduce the risk for infection. Injuries to deep structures, such as tendons and joint spaces, can be assessed.
Cat Bite Prophylaxis
Prophylaxis for uninfected-appearing cat bites is less controversial than prophylaxis for dog bites. Most cat bites, unless they are minor scratches or are limited to the superficial dermis, are candidates for oral prophylactic antibiotics. For prophylaxis to be effective, the first dose should be delivered in the emergency department and, preferably, in intravenous form. Either ampicillin/sulbactam or ceftriaxone plus metronidazole cover the likely pathogens (see Table 15-2 ). For outpatient management, amoxicillin/clavulanate also can be used. Alternatives and recommendations for children are found in Tables 15-1 and 15-2 .
Suturing
Unless tissue coverage and cosmesis are important considerations, cat bite and scratch wounds are probably best left open and unsutured. Cat fangs can penetrate deeply into the soft tissues, and because the infection potential of these wounds is great, the most judicious course of action is to cleanse, irrigate, and débride the wound and to leave it open. Another option is to open the wound with a simple incision as described previously in the section on bite wound management (see Fig. 15-1 ). Delayed primary closure can be used for wounds that need suturing for cosmetic or functional reasons, but primary closure at the time of wounding is considered too risky for inducing infection. Exceptions to this recommendation include large, easily cleansed lacerations that are not on the hand or the foot. Most lacerations of the face are protected by the good vascular supply of the face, and suturing is recommended for cosmesis. Whenever suturing is chosen, only percutaneous nonabsorbable sutures are used. Deep closures are avoided because of the increased risk of infection.
Established Cat Bite Infections
For initial empirical therapy, as with dog bites, an intravenous dose of ampicillin/sulbactam can be delivered in the emergency department (see Table 15-2 ). This agent can be continued during inpatient admission until culture results are known. For outpatient treatment, ampicillin/clavulanate can be prescribed for a full course of 14 days. This course can be modified with culture results and can be reviewed at the recommended 48- to 72-hour return visit. Infection with P. multocida is often characteristic with onset of symptoms within 24 hours of the bite, with prominent pain and swelling, and with a serosanguinous and grayish exudate. Intravenous antibiotic treatment is administered as soon as possible because of the rapid spread of this organism.
Human Bites
Microbiology
The microbiology of human bites differs from that of cat and dog bites and is more complex. Aerobic organisms recovered from human bite infections include Streptococcus (α-,β- hemolytic), Staphylococcus ( S. aureus, S. epidermidis ), and Corynebacterium . Eikenella corrodens has been recovered from 29% of human bites, including 25% of all clenched-fist injuries. E. corrodens is a particularly virulent organism that can result in serious, chronic, and indolent infections. Human bite infections in hospitalized or institutionalized patients often are caused by gram-negative organisms, such as Escherichia coli, Proteus, and Pseudomonas .
Infectious complications of human bites also can derive from viruses and other organisms. Viruses transmitted through human bites include hepatitis B and C and herpes virus types 1 and 2. Mycobacterium tuberculosis and Treponema pallidum have been reported to be transmitted through human bites. To date, although it is biologically possible, no case of human immunodeficiency virus infection has been reported from transmittal through a human bite.
Bite Wound Management
The basic wound care steps are carried out as previously described. For clenched-fist injuries (“fight bite”), both x-rays and exploration are recommended to rule out fractures and/or penetration of key structures such as joints or tendons. A fist struck against the mouth can drive teeth into the lightly padded knuckles. Suppurative complications are common, and violation to tendon, bone, or joint has been reported in 75% of cases. These injuries require aggressive intervention with exploration, irrigation, débridement, and early parenteral antibiotic administration. Care is best performed in consultation with a specialist.
Prophylaxis
Most authorities and clinicians recommend antibiotic prophylaxis for most human bites with the possible exception of superficial human bite wounds. Until reliable clinical studies are performed to clarify the true risk of human bites and the value of prophylaxis, it is best to err on the side of treatment. Uninfected nonhand bite wounds can be treated on an outpatient basis. Simple abrasions or superficial occlusional bites can be cleansed and observed. Antibiotics are given at the discretion of the caregiver (see Table 15-1 ). Wounds penetrating into the dermis or subcutaneous tissue are best treated with antibiotics. Any bite of the hand needs careful follow-up in addition to antibiotics. Because of the potential seriousness of these bites, consultative support is recommended. To ensure early and appropriate antibiotic levels, an initial parenteral dose of ampicillin/sulbactam should initiate prophylaxis. For children, amoxicillin plus clavulanate or trimethoprim/sulfamethoxazole plus clindamycin can be used.
Suturing
As a general rule, closure of human bite wounds traditionally has been avoided. A study has cast doubt, however, on the practice of not closing human bite wounds. Sutured versus nonsutured hand lacerations from human bites had the same outcome. Further studies are needed to confirm these results. Large, easily cleansed and irrigated proximal extremity or truncal wounds can be closed with a single layer of nonabsorbable material. Facial human bites can be disfiguring. A fresh facial bite (<24 hours old) that does not show signs of infection can be closed safely with sutures. Consultation is recommended when there is doubt about what management steps should be undertaken for human bites. All clenched-fist bite injuries, with penetration of the dermis, should be managed in consultation with a specialist.
Established Hand Infections
For established infections, ampicillin/sulbactam can be initiated intravenously in the emergency department (see Table 15-2 ). It provides excellent coverage against S. aureus, E. corrodens, and the relevant anaerobic species. Most patients with established hand infections are admitted to the hospital for continued intravenous antibiotics, and ampicillin/sulbactam can be continued until culture results are known. An alternative with similar good coverage against the relevant pathogens is ceftriaxone plus metronidazole. Children can be treated with cefuroxime or trimethoprim/sulfamethoxazole plus clindamycin. In human bites inflicted by institutionalized patients, coverage for gram-negative organisms should be considered, and the addition of an aminoglycoside to one of the above mentioned regimens might be indicated.
Rat Bites
Most reported rat bites occur in domestic settings. In a study of 50 cases, Staphylococcus epidermidis was the most common organism cultured from the open, fresh wound. Other organisms included Bacillus subtilis, diphtheroids, and α-hemolytic streptococci. Although 30% of wounds had positive cultures, only one case became infected. No patient was treated with prophylactic antibiotics. Antibiotics are recommended only if wound infection is evident. Ampicillin/clavulanate and doxycycline are recommended. Rats do not carry rabies, and patients do not need postexposure prophylaxis.
Fish Bites
People who work with or own fish are susceptible to infection by the small, gram-positive rod Erysipelothrix . This organism causes a slowly spreading cellulitis of the affected area, usually the hand. The organism responds to penicillin, ceftriaxone, and ciprofloxacin for patients who are allergic to penicillin.
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