Risk factors for surgical site infection after minor dermatological surgery. An analysis of individual participant data from four randomised controlled trial

Background: Surgical site infection (SSI) after dermatological surgery is associated with poor outcomes including increased recovery time, poor cosmesis and repeat visits to doctors. Prophylactic antibiotics are prescribed to reduce these adverse outcomes. Identifying risk factors for SSI will facilitate judicious antibiotic prophylaxis. Objectives: To identify risk factors for SSI after minor dermatological surgery. Design: Individual patient data from four large randomized controlled trials (RCTs) were combined to increase statistical power. Setting: Regional centre in North Queensland, Australia. Participants: A total of 3819 adult patients requiring minor skin procedures, were recruited for the four trials over a ten year period. Main Outcome Measure: Surgical site infection. Results: A total of 298 infections occurred in a population of 3819 patients, resulting in an overall incidence of 7.8% (95% CI 5.8-9.6), differing across the four studies (p=0.042). The risk factors identified were age (Relative Risk (RR) 1.01, 95% CI 1.001-1.020, p=0.008), excisions from the upper limbs (RR 3.03, 95% CI 1.76-5.22, p=0.007), lower limbs (RR 3.99, 95% CI 1.93-8.23, p=0.009) and flap/2-layer procedures (RR 3.23, 95% CI 1.79-5.85, p=0.008). Histology of the excised lesion was not a significant independent risk factor for infection. Conclusions: This study demonstrated that patients who were older, underwent complex excisions, or had excisions on the upper or lower limbs, were at higher risk of developing an SSI. An awareness of such risk factors will guide evidence based and targeted antibiotic prophylaxis.