Human Bites

Human bites are the third most common bite injuries following dog and cat bites; it is likely that 50% of the U.S. population will have been bitten by a human or animal during their lifetime.1–3 It has been estimated that as many as 150,000 human bites of humans occur annually but go unreported.⁴ This estimate includes bites to the hand that occur when an assailant punches a victim in the teeth. The population of human bite victims is usually between 20 and 30 years of age.⁵ Males are affected more frequently than are females.^6–8

Human bite injuries can be found in almost any anatomic location, including the face and head, upper and lower extremities, breasts, lips, cheeks, nose, ears, abdomen and thorax, and genitalia; more than 50% occur to the hands and are clenched fist injuries.4,6,9–12 Human bites are generally inflicted as a result of interpersonal violence and are typically associated with murder or attempted murder, rape, sexual assault, child abuse, burglary, and kidnapping.¹⁰ The incidence of human bite infections ranges from 4% of facial injuries to 50% of bites to the hand.^5,13–16 Human bites more commonly become infected than dog or cat bites.^2,17

Animal Bites

Approximately 4.5 million persons are bitten by animals each year; 15% of these will seek treatment from healthcare providers.1,6,9,18 Many of these wounds go unreported because some injuries may appear innocuous or because of social concerns. The overwhelming offender is the domesticated dog (85% to 90%), followed distantly by the domesticated cat (6% to 8%). In 2001, an estimated 368,245 patients were treated for dog bite–related injuries in hospital emergency departments.¹⁹ Wild animals, including skunks, raccoons, bats, foxes, and others, account for less than 6%. Other domesticated animals, including horses, cattle, and sheep, account for less than 3% of these bites. The rate of injury is higher among boys than girls; most victims are between 5 and 14 years of age, but many are younger than 5 years (Table 23-1).^20–23

Injury severity scales of children who are admitted to the hospital with dog bite injuries range from 1 to 25, with an average of 4 ± 5; the head and neck area is involved in almost 70% of these injuries.* This is in contrast to adult victims, who suffer only 5% to 15% of animal bites to the head and neck^19,26,27 (Fig. 23-1).

As many as 50% of dog bites may be reported as “unprovoked” (a possible indication of rabies infection), and more than 80% of these injuries involved the family’s or a neighbor’s pet.¹⁸ Breeds most often involved included pit bulls (25%), golden retrievers (12%), Labrador retrievers (12%), Chow Chows (10%), German shepherds (10%), Rottweilers (10%), and Doberman pinschers (5%) (Table 23-2).

There were 1164 deaths caused by nonvenomous animals from 1979 through 1990.²⁸ From 1995 to 1996, 279 human deaths occurred as a result of dog attacks.²⁹ During 1997 and 1998, at least 27 dog bite–related fatalities occurred.³⁰ Although some deaths involved hunters who were attacked by large animals, such as bears, most of the deaths were caused by large domesticated dogs, especially Pit bulls, Rottweilers, and German shepherds.²³ The most frequent reason for death is exsanguinating hemorrhage. The victims are usually infants (60%) or older individuals.²⁰

Human Bites

When humans chew, they generate forces in the range of 1.6 to 26.7 kg.31–34 Maximum molar bite forces range from a low of 1 kg to a high of 443 kg. Although human incisors shear, canines tend to puncture and molars crush. Thus, human bites can penetrate, avulse, and crush the tissue. These injuries are contaminated by a wide range of microorganisms (Box 23-1).*

More than 42 different species of bacteria have been reported in human saliva. Consideration must be given to all normal oral flora and common pathogens in the treatment of these contaminated crush injuries. Although the amount and type of inoculum may be minimal in the case of pristine dentition, they are of significant concern in the neglected mouth. More than 190 species have been isolated when gingivitis or periodontitis is present. The most common bacteria associated with human bite infections include Streptococcus, Staphylococcus aureus, Eikenella, Prevotella, Peptostreptococcus, Fusobacterium, and Candida spp. Immunocompromised patients, alcoholics, and diabetics are at a higher risk for infection by human bites. Other transmissible human diseases that are of concern include herpes, hepatitis B, hepatitis C, tuberculosis, and syphilis.37,38 Acquired immunodeficiency syndrome (AIDS) transmitted by saliva is considered to be of low or no risk, according to the Centers for Disease Control and Prevention (CDC). However, a number of case reports have listed a human bite as the likely event responsible for transmission of AIDS infection and the use of postexposure prophylaxis has been advocated.^2,39,40

Animal Bites

The force delivered by an animal’s jaw when biting can be as high as 1800 psi.41,42 This can result in devitalized tissue caused by crushing, tearing, avulsion, or a combination of all three. Furthermore, these wounds are contaminated by a broad spectrum of microorganisms and can cause a wide range of zoonotic diseases. Sharp, thin, long teeth more frequently cause puncture injuries, as in the case of the domesticated cat^6,20 (Fig. 23-2). Shorter, blunter, rounder teeth frequently cause a combination of penetrating and crush injuries, as in the case of the domesticated dog (Fig. 23-3). Flat teeth cause crush and tear injuries, as in the case of the domesticated horse (Fig. 23-4). Animal bites may cause fractures in addition to soft tissue injury, a thorough examination should be performed to prevent missing critical injuries, especially in infants, children, and older adults (Fig. 23-5).

A list of microorganisms from all animal bite sources is presented in Box 23-2.* No species seems to be associated with any particular type of bacterial variant, except that animal bites differ from human bites in the presence of Pasteurella multocida in as many as 50% to 75% of cases of infection. Consistent with the heterogeneity observed between feline and canine oropharyngeal Pasteurella strains, P. canis biotype 1 is the predominant isolate from dog bites, whereas P. multocida subsp. multocida and septica have been isolated much more frequently from cat bites.⁴⁹

The aerobic bacteria most frequently associated with infected animal bites include alpha- and beta-hemolytic streptococci (24% to 46%), S. aureus and S. epidermidis (10% to 25%), and Escherichia coli, Pseudomonas, and Moraxella spp. (10% to 25%).† The most common anaerobic bacteria isolated from infected animal bites are the Bacteroides, Prevotella, and Fusobacterium spp. (13% to 76%). Oral and environmental fungi may also contaminate bite wounds. Candida spp. have been isolated from 8% of infected human bites, but their pathogenic role remains unclear.^51,52