Dog and Cat Bites: Complex Infections

To define better the bacteria responsible for infections of dog and cat bites, the authors conducted a prospective study at 18 emergency departments. To be eligible for enrollment, patients had to meet one of three major criteria for infection of a bite (fever, abscess, and lymphangitis) or four of five minor criteria (wound-associated erythema, tenderness at the wound site, swelling at the site, purulent drainage, and leukocytosis). Wounds were cultured for aerobic and anaerobic bacteria.

The most common site for bites was the hand (50% for dogs and 63% for cats). The infected wounds of 50 patients with dog bites and 57 patients with cat bites yielded a median of 5 bacterial isolates per culture. Aerobes and anaerobes were isolated from 56 percent of the wounds (aerobes alone from 36 percent, and anaerobes alone from 1 percent); 7 percent of cultures had no growth. Pasteurella species were the most frequent isolates from both dog bites (50 percent) and cat bites (75 percent). Pasteurella canis was the most common isolate of dog bites, and Pasteurella multocida was the most common isolate of cat bites. Other common aerobes included streptococci, staphylococci, moraxella, and neisseria. Common anaerboes included fusobacterium, and bacteroides.

Approximately 20 percent of the infections in this study were treated empirically with penicillin, ampicillin, or a first-generation cephalosporins alone, choices that appear to be less than optimal .

The authors suggest that empirical therapy for dog bites and cat bites should be directed against pasteurella, streptococci, staphylococci, and anaerobes. Pasteurella species are usually susceptible to ampicillin, penicillin, second-generation and third-generation cephalosporin, doxycycline, trimethoprim-sulfamethoxazole, fluoroquinolones, clarithromycin, and azithromycin.

(Talan D et al. Bacteriologic analysis of infected dog and cat bites. N Eng J Med 1999; 340(2):85-92)

COMMENT: School nurses can monitor wound healing and report to physicians when an antibiotic is not doing its job.