Estimates indicate that each year more than 2 million people across the United States are bitten by animals. Dog bites account for more than 90% of these injuries, and cat bites account for most of the remainder.[1] Although wild animal bites are rare, they are potentially more serious, given the risk of rabies and other infections. One half of all animal bites are trivial and require no medical treatment; only 10% are severe enough to require suturing, and only 2% result in hospitalization. Bite wounds account for an estimated 1% of pediatric visits to an emergency department.[1] Children experience the greatest number of animal bites (the peak age group is 5 to 14 years), with 50% of all school-aged children reporting an animal bite at some point in their life. With dog bites, adults are bitten on an extremity; children, however, are bitten primarily on the head or neck 75% of the time.[2] Boys are twice as likely to be bitten by a dog, whereas girls receive twice as many cat bites.[2] Not surprisingly, most of the animals live in the victim's neighborhood (75%) or home (15%); in most instances, the bites are provoked by humans.[1]

The major morbidity from animal bites results from direct trauma and infection. Although dog bites are more likely to cause lacerations or avulsions, these open wounds can be debrided and cleaned to prevent infection. However, puncture wounds, which usually do not require suturing, can result in deep-tissue infections.[3]

As shown in Table 235-1, the risk of infection varies according to several factors. Hand wounds are most likely to become infected, partly because of the type of wound (most frequently a puncture wound), the relatively poor vascular supply, and the vulnerability of the closed spaces of the hand. If more than 24 hours have elapsed before medical attention is sought, then the risk of infection is greatly increased. Cat and human bites pose a greater risk of infection than dog bites, partly because these bites more often cause puncture wounds, whereas dog bites frequently cause open lacerations.

Most bacteria associated with bite wounds are common organisms that reside in the animal's oral cavity. Bacteria on the victim's skin may also contribute to infection. Most infections involve several pathogens,[3] often both aerobes and anaerobes. Pasteurella multocida, a gram-negative, facultative anaerobe found in the mouths of most dogs and cats, is highly associated with cat bite infections (up to 80%) and to a lesser extent with dog bite infections (12%-50%). Although the exact prevalence of other pathogenic bacteria isolated from infected animal bites varies, gram-negative aerobes (eg, Pseudomonas, Klebsiella, and Enterobacter species) are found more often than gram-positive aerobes (eg, staphylococci, streptococci) or anaerobes (eg, Bacteroides, Fusobacterium, and Peptococcus species).[4]

Another group of gram-negative bacteria, classified by the Centers for Disease Control and Prevention as alphanumeric organisms, has frequently been isolated from dog bite wounds. Interestingly, human bites are rarely infected by P multocida but are often associated with gram-positive organisms, gram-negative anaerobes, or Eikenella corrodens, a genus almost unique to human bites that in rare cases is found in cat bites. Human bites have the potential to transmit the HIV and hepatitis B virus and should be evaluated in persons who are bitten by those at high risk for infection.