Teenager With Cat Bite

A 16-year-old boy visiting his aunt and uncle at a cabin in the country was bitten by their cat earlier in the day. He tried to pick up the animal after it had been injured, and it bit him on the dorsum of the hand between the thumb and first finger.

HISTORY

The patient's hand was washed and dressed at the time of the bite. The family took the cat to a veterinarian, who diagnosed a leg fracture and offered to keep the animal at his facility for the remainder of the week. The cat was otherwise healthy.

PHYSICAL EXAMINATION

The patient's vital signs are normal. There is a deep puncture wound on the dorsum of his right hand as well as a 1- to 2-cm tear related to the puncture. Neurologic functions are intact. A surgical consultant recommends that the wound be left open for now and reevaluated in 48 hours.

Which of the following is the optimal regimen for this patient?A. Intravenous ampicillin for 5 days.
B. Oral dapsone for 7 to 10 days.
C. Oral amoxicillin-clavulanate for 7 to 10 days.
D. No antibiotic therapy.
E. Rabies prophylaxis.

(Answer on next page.)

CORRECT ANSWER: C

The treatment of an animal bite wound involves a number of decisions:

• Whether to close the wound surgically or leave it open.
• Whether antibiotic therapy is warranted-and if so, which agents and what route of administration are most appropriate.
• Whether rabies prophylaxis is required.

Wound closure. The decision to close a wound surgically depends on the location of the wound, the nature of the wound, and how much time has elapsed since the bite. Cosmetic results must be weighed against infection risks. Facial wounds, for example, are usually closed for cosmetic reasons; however, most puncture wounds, lacerations that are not potentially disfiguring, and extremity wounds are left open.¹ Extremity wounds more than 6 to 12 hours old and facial wounds more than 12 to 24 hours old are best left open.¹

Antibiotic therapy. The issue of when to administer antibiotic prophylaxis for animal bite wounds is somewhat controversial. Such wounds are associated with a 2% to 5% risk of infection, and antibiotic therapy probably reduces that risk to a statistically significant degree.¹ Prophylaxis is generally warranted for the following "high-risk" wounds:

• Deep punctures.
• Bites inflicted by cats.
• Wounds that require surgical repair.
• Bites on the hands.

This patient's injury meets 3 of these criteria; thus, he is a candidate for antibiotic therapy.

An elegant study of the bacteriology of infected dog and cat bites in 107 patients (50 dog bites, 57 cat bites) provides guidance on antibiotic selection. Talan and colleagues² found a mixed bacteriology dominated by Pasteurella species-Pcanis in dog bites and P multocida and P septica in cat bites. The treatment most often given in this study was a b-lactam antibiotic together with a b-lactamase inhibitor, a combination that the authors deemed appropriate in light of their bacteriologic findings.

Thus, ampicillin alone (choice A), via any route of administration, would not be adequate for this patient. However, amoxicillin together with clavulanate (choice C) is an appropriate choice. Patients with overtly infected wounds are usually given antibiotics intravenously. Because this patient's wound is not overtly infected, oral administration suffices.

Dapsone (choice B) is a sulfa derivative that, despite very tenuous evidence for in vivo efficacy, is routinely given to patients with brown recluse spider bites. Its use is not based on its antibacterial properties but rather on in vitro evidence of its capacity for polymorphonuclear inhibition, a mechanism that is believed to be instrumental in counteracting the profound inflammatory effect of recluse spider bites.³ In any event, this patient's bite was inflicted by a cat and thus has an entirely different microbiology and pathology. Dapsone has no role here.

Rabies prophylaxis. The risk of rabies and need for prophylaxis must be carefully considered in any patient with a mammal bite. There is a hierarchy of risk across mammalian species (eg, a very high risk in bats and a very low risk in rats, with the risk in dogs and cats falling somewhere in between).

The cat that bit this patient was not exhibiting particularly wild, aggressive, or unusual behavior. The animal was healthy before the bite and probably was reacting to its leg injury. Moreover, the cat was evaluated by a veterinarian and remains under his care so that any signs of illness can be observed. Thus, rabies prophylaxis is not required at this time.

Outcome of this case. No signs of infection developed, and the patient's wound healed appropriately over the next week with minimal cosmetic effects. The cat was released to its owners after a week and remains healthy.