Epidemiology

During the past 3 decades, there have been approximately 20 deaths per year in the USA from dog-inflicted injuries; 65% of these occurred in children younger than 11 yr. The breed of dog involved in attacks on children varies; Table 705-1 depicts the risk index by breed from one study of 341 dog bites. Rottweilers, pit bulls, and German shepherds accounted for more than 50% of all fatal bite-related injuries. Unaltered male dogs account for approximately 75% of attacks; nursing dams often inflict injury to humans when children attempt to handle one of their puppies.

The majority of dog-related attacks occur in children between the ages of 6 and 11 yr. Boys are attacked more often than girls (1.5 : 1). Approximately 65% of the attacks occur around the home, 75% of the biting animals are known by the children, and almost 50% of the attacks are said to be unprovoked. Similar statistics apply in Canada, where 70% of all bites reported in one study were sustained by children between 2 and 14 yr; 65% of the dogs involved in the biting were part of the family or extended family and occurred in someone’s home.

Of the approximately 450,000 reported cat bites per year occurring in the USA, nearly all are inflicted by known household animals. Because rat bites and gerbil bites are not reportable conditions, little is known about the epidemiology of these injuries or the incidence of infection after rodent-inflicted bites or scratches.

Few data exist on the incidence and demographics of human bite injuries in pediatric patients; however, preschool and early school-aged children appear to be at greatest risk of sustaining an injury from a bite by a human. Human bites are a common cause of injury in daycare centers in the USA, although in some series the proportion of human bites is highest among adolescents. In adolescents, fist-to-mouth (tooth) injuries are associated with fights.

Clinical Manifestations

Dog bite–related injuries can be divided into three, almost equal categories: abrasions, puncture wounds, and lacerations with or without an associated avulsion of tissue. Dog bites may be crush injuries. The most common type of injury from cat and rat bites is a puncture wound. Cat bites often penetrate to deep tissue. Human bite injuries are of two types: an occlusion injury that is incurred when the upper and lower teeth come together on a body part and, in older children and young adults, a clenched-fist injury that occurs when the injured fist, usually on the dominant hand, comes in contact with the tooth of another individual.

Diagnosis

Management of the bite victim should begin with a thorough history and physical examination. Careful attention should be paid to the circumstances surrounding the bite (e.g., type of animal [domestic or sylvatic], whether the attack was provoked or unprovoked, location of the attack); a history of drug allergies; and the immunization status of the child (tetanus) and animal (rabies). During physical examination, meticulous attention should be paid to the type, size, and depth of the injury; the presence of foreign material in the wound; the status of underlying structures; and, when the bite is on an extremity, the range of motion of the affected area. A diagram of the injury should be recorded in the patient’s medical record. A radiograph of the affected part should be obtained if there is likelihood that a bone or joint could have been penetrated or fractured or if foreign material is present. The possibility of a fracture or penetrating injury of the skull should be considered in individuals, particularly infants, who have sustained dog bite injuries to the face or head.

Complications

Infection is the most common complication of bite injuries, regardless of the species of biting animal. The decision to obtain material for culture from a wound depends on the species of the biting animal, the length of time that has elapsed since the injury, the depth of the wound, the presence of foreign material contaminating the wound, and whether there is evidence of infection. Although potentially pathogenic bacteria have been isolated from up to 80% of dog bite wounds that are brought to medical attention within 8 hr after the bite, the infection rate for wounds receiving medical attention in <8 hr is small (2.5-20%). Thus, unless they are deep and extensive, dog bite wounds that are less than 8 hr old do not need to be cultured unless there is evidence of contamination or early signs of infection or the patient is immunocompromised. Species of Capnocytophaga canimorsus, uncommon pathogens in bite-inflicted injuries, have been isolated from nearly 5% of infected wounds in immunocompromised patients. The infection rate in cat bite wounds that receive early medical attention is at least 50%; therefore, it is prudent to obtain material for culture from all but the most trivial cat-inflicted wounds and from all other animal bite wounds that are not brought to medical attention within 8 h, regardless of species of the biting animal.

The rate of infection after rodent bite injuries is not known. Most of the oral flora of rats is similar to that of other mammals; however, approximately 50% and 25% of rats harbor strains of Streptobacillus moniliformis and Spirillum minus, respectively, in their oral flora. Each of these agents has the potential to cause infection (Chapter 705.1).

All human bite wounds, regardless of the mechanism of injury, should be regarded as carrying high risk for infection and should be cultured. Because of the high incidence of anaerobic infection after bite wounds, it is important to obtain material for anaerobic as well as aerobic cultures.

Common causes of soft tissue bacterial infections after dog, cat, or human bites are noted in Table 705-2. High risk for infection after a bite is associated with wounds in the hand, foot, or genitals, penetration of bone or tendons, human or cat bites, delay in treatment longer than 24 hr, presence of foreign material, immunosuppression (asplenia), and crush or deep puncture wounds.

Treatment (Table 705-3)

After the appropriate material has been obtained for culture, the wound should be anesthetized, cleaned, and vigorously irrigated with copious amounts of normal saline. Irrigation with antibiotic-containing solutions provides no advantage over irrigation with saline alone and may cause local irritation of the tissues. Puncture wounds should be thoroughly cleansed and gently irrigated with a catheter or blunt-tipped needle; high-pressure irrigation should not be employed. Avulsed or devitalized tissue should be debrided and any fluctuant areas incised and drained.

Table 705-3 PROPHYLACTIC MANAGEMENT OF HUMAN OR ANIMAL BITE WOUNDS TO PREVENT INFECTION

CATEGORY OF MANAGEMENT	MANAGEMENT
Cleansing	Sponge away visible dirt. Irrigate with a copious volume of sterile saline solution by high-pressure syringe irrigation.*
	Do not irrigate puncture wounds. Standard precautions should be used.
Wound culture	No for fresh wounds, unless signs of infection exist.
	Yes for wounds more than 8-12 hr old and wounds that appear infected.†
Radiographs	Indicated for penetrating injuries overlying bones or joints, for suspected fracture, or to assess foreign body inoculation.
Debridement	Remove devitalized tissue.
Operative debridement and exploration	Yes for one of the following conditions: • Extensive wounds (devitalized tissue) • Involvement of the metacarpophalangeal joint (closed-fist injury) • Cranial bites by large animal

Wound closure Yes for selected fresh, nonpuncture bite wounds (see text) Assess tetanus immunization status Yes Assess risk of rabies from animal bites Yes Assess risk of hepatitis B virus infection from human bites Yes Assess risk of human immunodeficiency virus from human bites Yes Initiate antimicrobial therapy Yes for any of the following:

Follow-up Inspect wound for signs of infection within 48 hr

* Use of 18-gauge needle with a large-volume syringe is effective. Antimicrobial or anti-infective solutions offer no advantage and may increase tissue irritation.

^† Both aerobic and anaerobic bacterial culture should be performed.

Modified from American Academy of Pediatrics. Bite wounds. In Pickering LK, Baker CJ, Long SS, et al, editors: Red book: 2006 report of the committee on infectious disease, ed 27, EIk Grove Village, IL, 2006, AAP, pp 191–195.

There is much controversy about, and few data exist to determine, whether bite wounds should undergo primary closure or delayed primary closure (3-5 days) or should be allowed to heal by secondary intention. Factors to be considered are the type, size, and depth of the wound; the anatomic location; the presence of infection; the time since the injury; and the potential for cosmetic disfigurement. Surgical consultation should be obtained for all patients with deep or extensive wounds; wounds involving the face or bones and joints; and infected wounds that require open drainage. Although there is general agreement that infected wounds and those that are older than 24 hr should not be sutured, there are disagreement about and varying clinical experience with the efficacy and safety of closing wounds that are less than 8 hr old with no evidence of infection. Because all hand wounds are at high risk for infection, particularly if there has been disruption of the tendons or penetration of the bones, delayed primary closure is recommended for all but the most trivial bite wounds of the hands. Facial lacerations are at smaller risk for secondary infection because of the more luxuriant blood supply to this region. Many plastic surgeons advocate primary closure of facial bite wounds that have been brought to medical attention within 6 hr and have been thoroughly irrigated and debrided.

Few studies unequivocally demonstrate the efficacy of antimicrobial agents for prophylaxis of bite injuries. There is general consensus that antibiotics should be administered to all victims of human bites and all but the most trivial of dog, cat, and rat bite injuries, regardless of whether there is evidence of infection. The bacteriology of bite wound infections is primarily a reflection of the oral flora of the biting animal and, to a lesser extent, of the skin flora of the victim (see Table 705-2). Because each of the multitudes of aerobic and anaerobic bacterial species that colonize the oral cavity of the biting animal has the potential to invade local tissue, multiply, and cause tissue destruction, most bite wound infections are polymicrobial. Evidence suggests that as many as five different species may be isolated from infected dog bite wounds.

Despite the large degree of homology in the bacterial flora of the oral cavity among humans, dogs, and cats, important differences exist between the biting species, and they are reflected in the type of wound infections that occur. The predominant bacterial species isolated from infected dog bite wounds are Staphylococcus aureus (20-30%), Pasteurella multocida (20-30%), Staphylococcus intermedius (25%), and C. canimorsus; approximately one half of dog bite wound infections contain mixed anaerobes. Similar species are isolated from infected cat bite wounds; however, P. multocida is the predominant species in at least 50% of cat bite wound infections. At least 50% of rats harbor strains of Streptobacillus moniliformis in the oropharynx, and approximately 25% harbor Spirillum minor, an aerobic gram-negative organism. In human bite wounds, nontypable strains of Haemophilus influenzae, Eikenella corrodens, S. aureus, α-hemolytic streptococci, and β-lactamase–producing aerobes (about 50%) are the predominant species. Clenched-fist injuries are particularly prone to infection by Eikenella spp. (25%) and anaerobic bacteria (50%).

The choice between oral and parenteral antimicrobial agents should be based on the severity of the wound, the presence and degree of overt infection, signs of systemic toxicity, and the patient’s immune status. Amoxicillin-clavulanate is an excellent choice for empirical oral therapy for human and animal bite wounds because of its activity against most of the strains of bacteria that have been isolated from infected bite injuries. Similarly, ticarcillin-clavulanate or ampicillin and sulbactam are preferred for patients who require empirical parenteral therapy. Procaine penicillin remains the drug of choice for prophylaxis and treatment of rat-inflicted injuries. First-generation cephalosporins have limited activity against P. multocida and E. corrodens and, therefore, should not be used for prophylaxis or empirical initial therapy of bite wound infections. The therapeutic alternatives for penicillin-allergic patients are limited, because the traditional alternative agents are generally inactive against one or more of the multiple pathogens that cause bite wound infections. Although erythromycin is commonly recommended as an alternative agent for penicillin-allergic patients who have suffered dog and cat bites, it has incomplete activity against strains of P. multocida and S. moniliformis and is not effective against E. corrodens. Similarly, clindamycin and the combination trimethoprim-sulfamethoxazole have limited activity against strains of P. multocida and anaerobic bacteria, respectively. Azithromycin and the ketolide antibiotics may be considered because they have activity against aerobic and anaerobic bacteria that are present in infected bite wounds. Tetracycline is the drug of choice for penicillin-allergic patients who have sustained rat bite injuries.

Although tetanus occurs only rarely after human or animal bite injuries, it is important to obtain a careful immunization history and to provide tetanus toxoid to all patients who are incompletely immunized or those in whom it has been longer than 10 yr since the last immunization. The need for postexposure rabies vaccine in victims of dog and cat bites depends on whether the biting animal is known to have been vaccinated and, most importantly, on local experience with rabid animals in the community (Chapter 266). In developing countries, bites from dogs, cats, foxes, skunks, and raccoons carry a high risk of rabies. Annually worldwide, animal bites result in more than10 million postexposure treatments. An estimated 55,000 deaths due to rabies occur each year, although this number probably represents an underestimation. Most deaths occur in low-income families in developing countries. The local health department should be consulted for advice in all instances in which the vaccination status of the biting animal is unknown and whether there is known endemic rabies in the community. Postexposure prophylaxis for hepatitis B should be considered in the rare instance in which an individual has sustained a human bite from an individual who is at high risk for hepatitis B (Chapter 350).

All but the most trivial bite wounds of the hand should be immobilized in position of function for 3-5 days, and patients with bite wounds of an extremity should be instructed to keep the affected extremity elevated for 24-36 hr or until the edema has resolved. All bite wound victims should be reevaluated within 24-36 hr after the injury.

Prevention

It is possible to reduce the risk of injury with anticipatory guidance. Parents should be routinely counseled during prenatal visits and routine health maintenance examinations about the risks of having potentially biting pets in the household. All patients should be cautioned against harboring exotic animals for pets. Additionally, parents should be made aware of the proclivity of certain breeds of dogs to inflict serious injuries and the protective instincts of nursing dams. All young children should be closely supervised, particularly when in the presence of animals, and from a very early age should be taught to respect animals and to be aware of their potential to inflict injury (Tables 705-4 and 705-5).

Table 705-4 CODE OF BEHAVIOR WHEN HANDLING A DOG

DOG CHARACTERISTICSS	RECOMMENDED HUMAN BEHAVIOR
Dogs sniff as a means of communication.	Before petting a dog, let it sniff you.
Dogs like to chase moving objects.	Do not run past dogs.
Dogs run faster than humans.	Do not try to outrun a dog.
Screaming may incite predatory behavior.	Remain calm if a dog approaches.
The order of precedence needs to be in evidence.	Do not hug or kiss a dog.
Direct eye contact may be interpreted as aggression.	Avoid direct eye contact.
Dogs tend to attack extremities, face, and neck.	If attacked, stand still (feet together) and protect neck and face with arms and hands.
Lying on the ground provokes attacks.	Stand up. If attacked while lying, keep face down and cover the ears with the hands. Do not move.
Fighting dogs bite at anything that is near.	Do not try to stop 2 fighting dogs.

From Schalamon J, Ainoedhofer H, Singer G, et al: Analysis of dog bites in children who are younger than 17 years, Pediatrics 117:e374–e379, 2006.

Reduction of the rate of human bite injuries, particularly in daycare centers and schools, can be achieved by good surveillance of the children and adequate supervisory personnel-to-child ratios.

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