Dog Bites

Dogs account for 80 to 90 percent of reported animal bites in the United States.23 Boys are victims of dog bites twice as often as girls, and the dog is known to the victim in about 90 percent of cases. Dog bite injuries occur most frequently on the extremities (upper slightly more often than lower), followed by the head and neck, and least frequently on the trunk. Head and neck bites are more common in children. Infection occurs in dog bites in approximately 5 percent of cases. Factors that increase the rate of infection include (1) victim age greater than 50 years, (2) delay in seeking treatment greater than 24 h, (3) hand wounds, and (4) deep puncture wounds. Dog bites are rarely lethal, but they may produce significant damage secondary to the force delivered—approximately 150 to 450 psi. 2728

Infection of dog bite wounds usually results from the organisms inoculated into the depth of the wound by the animal's teeth, not from the bacterial flora normally found on the patient's skin. Infections from dog bite wounds are often polymicrobial; aerobic bacteria are present in most wounds and anaerobic bacteria are found in up to 40 percent.25 Aerobic isolates are usually alpha-hemolytic streptococci, followed by S. aureus, Pasteurella multocida, and S. intermedius. Other pathogenic aerobes include b-hemolytic streptococci, g-hemolytic streptococci, E. corrodens, Capnocytophaga canimorsus, other Pasteurella sp., and Haemophilus aphrophilus. Anaerobic bacteria isolated from dog bite wounds include Actinomyces sp., Bacteroides sp., Fusobacterium sp., and Peptostreptococcus sp.

Capnocytophaga canimorsus, formerly known by the Centers for Disease Control and Prevention as "dysgonic fermenter-2" (DF-2), is a fastidious, thin, gram-negative bacillus that has been associated with severe infection in immunocompromised patients (asplenia, alcoholism, chronic lung disease, or other immunosuppression). It was first recognized as a human pathogen in 1976. Infection with this organism may produce severe sepsis with disseminated intravascular coagulation, acute renal failure, endocarditis, peripheral gangrene, and cardiopulmonary failure. Fatalities are seen in up to 25 percent of cases. Penicillin is the drug of choice when infection with this organism is suspected and should be used prophylactically in high-risk individuals. This bacterium is also usually sensitive to cephalosporins, tetracyclines, erythromycin, and clindamycin.

Lacerations of the scalp, face, and trunk from dog bites can be irrigated, debrided, and sutured in the ED with a low risk of infection. 2 30 Lacerations of the distal extremities, especially the feet and hands, should not be sutured. Lacerations of the proximal extremities—the upper arm and the thigh—can probably be closed after irrigation and exploration. Large, extensive lacerations, especially in small children, are best explored and repaired in the operating room. 27

Discharge instructions should include information about signs and symptoms of infection and assurance of follow-up within 24 to 48 h. Bites to the hand, and wounds in high-risk individuals should receive prophylactic treatment with amoxicillin/clavulanate, clindamycin plus ciprofloxacin, or clindamycin plus trimethoprim-sulfamethoxazole for 3 to 5 days. Antibiotics should be initiated in the ED. There is no evidence that antibiotic therapy for dog bite wounds in other anatomic locations is beneficial.

Wounds obviously infected at the time of presentation need to be cultured and antibiotic therapy must be initiated. Infection developing within 24 h after injury suggests P. multocida and treatment with penicillin, ciprofloxacin, or trimethoprim-sulfamethoxazole is recommended. Wound infection developing beyond 24 h after the dog bite implicates Staphylococcus and Streptococcus; treatment with a penicillinase-resistant penicillin or first-generation cephalosporin is indicated. Low-risk patients with local cellulitis only and no involvement of underlying structures can be treated and observed closely as outpatients. Admission and parenteral antibiotic therapy are indicated in patients with infected wounds and evidence of lymphangitis, lymphadenitis, tenosynovitis, septic arthritis, or osteomyelitis; systemic signs such as fever; or injury to underlying structures such as tendons, joints, or bone. Aerobic and anaerobic cultures should be obtained from the deep structures, preferably during exploration in the operating room. Initial antibiotic therapy should begin with ampicillin/sulbactam or clindamycin plus ciprofloxacin. If the Gram stain shows gram-negative bacilli, a third- or fourth-generation cephalosporin or aminoglycoside should be added. When sepsis is present, broad-spectrum coverage with imipenem/cilastatin is warranted pending culture results.

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