Bacteriologic analysis of infected dog and cat bites

Background and Methods To define better the bacteria responsible for infect ions of dog and cat bites, we conducted a prospective study at 18 emergency departments. To be eligible for enrollment, patients had to meet one of th ree major criteria for infection of a bite wound (fever, abscess, and lymph angitis) or four of five minor criteria (wound-associated erythema, tendern ess at the wound site, swelling at the site, purulent drainage, and leukocy tosis). Wound specimens were cultured for aerobic and anaerobic bacteria at a research microbiology laboratory and, in some cases, at local hospital l aboratories. Results The infected wounds of 50 patients with dog bites and 57 patients w ith cat bites yielded a median of 5 bacterial isolates per culture (range, 0 to 16) at the reference laboratory. Significantly more isolates grew at t he reference laboratory than at the local laboratories (median, 1; range, 0 to 5; P<0.001). 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 fre quent isolates from both dog bites (50 percent) and cat bites (75 percent). Pasteurella canis was the most common isolate of dog bites, and Past. mult ocida subspecies multocida and septica were the most common isolates of cat bites. Other common aerobes included streptococci, staphylococci, moraxell a, and neisseria. Common anaerobes included fusobacterium, bacteroides, por phyromonas, and prevotella. Isolates not previously identified as human pat hogens included Reimerella anatipestifer from two cat bites and Bacteroides tectum, Prevotella heparinolytica, and several porphyromonas species from dog and cat bites. Erysipelothrix rhusiopathiae was isolated from two cat b ites. Patients were most often treated with a combination of a beta-lactam antibiotic and a beta-lactamase inhibitor, which, on the basis of the micro biologic findings, was appropriate therapy. Conclusions Infected dog and cat bites have a complex microbiologic mix tha t usually includes pasteurella species but may also include many other orga nisms not routinely identified by clinical microbiology laboratories and no t previously recognized as bite-wound pathogens. (N Engl J Med 1999;340: 85 -92.) (C) 1999, Massachusetts Medical Society.