Objectives To determine a current infection rate of dog bite wounds and predictors of wounds at risk for infection that may benefit from prophylactic antibiotics.

Methods A prospective multicentre observational study was conducted over 4.5 years. At the time of treatment Emergency Physicians completed a structured data form evaluating patient, wound and treatment characteristics of patients with dog bite wounds. Patients were followed up at 30 days to assess for infection. Predictor variables were analysed with univariate analysis, using either χ², parametric or nonparametric methods where appropriate. Significant variables and those with important interactions on univariate analysis were considered in a logistic regression (LR) analysis.

Results 495 patients with dog bites were enrolled and 345 had complete follow-up. Eighteen patients (5.2%, 95% CI 3.1% to 8.1%) had bites that became infected. On univariate analysis, only puncture wounds were found to be significantly associated with infection RR 2.8 (95% CI 1.2 to 6.9). However, location and wound closure met criteria for entry into the model having important interactions; facial wounds had a higher risk of infection than anticipated but were also more likely to be closed (p < 0.0001). A LR model considering puncture wounds, wound closure and wound location found that puncture wounds (OR 4.1 [95% CI 1.4 to 11.7]) and wound closure (OR 3.1 [95% CI 1.03 to 9.0]) were independent predictors of infection. The incidence of infection in wounds that were not punctured or closed during treatment was only 2.6% (95% CI 0.7% to 6.5%).

Conclusions Puncture wounds or wounds closed during treatment are dog bite wounds at a high risk of infection and should be considered for treatment with prophylactic antibiotics.