Do All Human Bite Wounds Need Antibiotics?

Source: Broder J, et al. Low risk of infection in selected human bites treated without antibiotics. Am J Emerg Med 2004;22:10-13.

Abstract & Commentary

Most emergency medicine textbooks agree that human bite wounds, as well as dog and cat bite wounds, require antibiotic prophylaxis in addition to usual wound care practices. This study from the University of Maryland challenges this belief, and attempts to define a group of human bites at low risk of infection that do not require any antibiotic prophylaxis.

This prospective, double-blind, placebo-controlled study randomized patients with certain superficial human bite wounds to antibiotic or placebo treatment in an attempt to determine whether these wounds had similar rates of infection. Patients were eligible for enrollment if the bite wound was superficial (i.e., penetrating only the epidermis) and did not involve hands, feet, or skin overlying joints or cartilaginous structures. Exclusion criteria included immune-compromised status, age younger than 18 years, bites older than 24 hours, and allergy to penicillin or related compounds. No patients with puncture-type bite wounds were enrolled.

Patients meeting entry criteria were randomized into the placebo or antibiotic arm of the study. Wounds were debrided as necessary and irrigated with 500 cc of normal saline. Tetanus prophylaxis was given as necessary. No wounds required sutures. Patients then were discharged from the emergency department with a five-day course of either cephalexin plus penicillin or placebo, and were instructed to return at 48 and 96 hours to be checked for signs of infection. All wounds were rechecked by the same examiner (blinded to treatment group) to eliminate the possibility of inter-rater variation in the assessment of whether wound infection was present.

One hundred-twenty-seven (127) patients were enrolled. One patient in each group was lost to follow-up, leaving 125 patients completing the protocol. The two groups were similar with respect to age and weight.

None of the 63 patients in the antibiotic group developed wound infections (0%, 95% CI 0-4.6%), and one of 62 patients in the placebo group developed wound infection (1.6%, 95% CI 0-7.3%). The groups were similar in terms of medication compliance, and no patient developed an allergic reaction.

The authors conclude that this study supports changing the practice of routinely giving antibiotic prophylaxis to patients with these specific types of human bite wounds.

Commentary by Jacob W. Ufberg, MD

This study supports a more common-sense approach to human bite wounds: Very superficial wounds in low-risk body areas that are given meticulous wound care are unlikely to become infected. While the study is limited by small numbers, even the wide confidence intervals do not exceed wound infection rates commonly seen among the wounds we treat in the emergency department.

Caution should be exercised, however, in putting these guidelines into practice. We must be sure that the wounds meet the authors’ criteria if we are to withhold antibiotics. Puncture wounds, deeper lacerations, and bites to the hand all have been shown to have high infection rates, which may be lowered by antibiotic prophylaxis. Also, we should not extrapolate these results to include dog and cat bites, which are more likely to cause deeper lacerations and puncture-type wounds due to the differences in shape between human and animal teeth.

Dr. Ufberg, Assistant Professor of Emergency Medicine, Assistant Residency Director, Department of Emergency Medicine, Temple University School of Medicine, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.