Preoperative risk prediction of surgical site infection requiring hospitalization or reoperation in patients undergoing vascular surgery

Objective The objective of this study was to develop a surgical site infection (SSI) prediction score for risk assessment before elective vascular surgery. Methods We conducted a nested case-control study among patients who underwent elective vascular (abdominal aortic and peripheral arterial) surgery from January 1, 2003, to December 31, 2007, at Mayo Clinic (Rochester, Minn) an academic tertiary surgical center. Cases were patients with SSI requiring hospitalization; controls (one or two per case) were matched on type of procedure and date of surgery. Clinical data were collected by chart review. A risk score based on preoperative variables was developed using multivariable logistic regression and bootstrap resampling. The C statistic, equivalent to the area under the receiver operating characteristic curve, was used to assess discrimination. Calibration was assessed by plotting percentile risk groups of model-predicted values against observed proportions of subjects with SSI. Results Eighty-four cases were compared with 160 controls. Preoperative variables independently associated with SSI risk were critical limb ischemia, previous SSI, prior revascularization procedure, and chronic obstructive pulmonary disease. A prediction model containing these variables was developed (model and risk score C statistic of 0.737 and 0.727, respectively). The calibration curve did not appear to deviate appreciably from the 45-degree line of identity. Conclusions We developed an SSI risk score based on noninvasive preoperative variables with acceptable discrimination and calibration. This tool needs prospective and external validation.