Extended postoperative prophylactic antibiotic therapy in posterior instrumented spinal surgery: a pilot study

Background: Surgical site infection (SSI) following posterior instrumented surgery has the potential to adversely affect individual patient outcomes and also simultaneously represents a global healthcare burden. This study aimed to evaluate the impact of an extended 2-week course of oral antimicrobial prophylaxis (AMP) on reducing SSI rate following posterior instrumented spinal surgery. Methods: A retrospective single centre cohort study over a period of 18 months at a tertiary hospital was conducted on patients undergoing posterior instrument spinal surgery. A standard 24 hours antibiotic post-operative course was compared to an extended 2-week course. The primary outcome measure was rate of gram-positive SSI, return to theatre (RTT) for gram-positive SSI, and the rate of overall complications and infections. Univariate analysis was performed to determine if there was any significant difference between the standard and extended anti-microbial regimens. Multivariate logistic regression analysis was constructed to examine for independent risk factors off SSI. Results: Two hundred and fifty-five consecutive patients were deemed eligible. There were 194 patients (76%) in the standard cohort and 61 patients (24%) in the extended arm. The extended AMP cohort showed more favourable absolute rates in all outcome metrics: gram-positive SSI (0% vs. 2.5%, P=0.34), RTT for gram-positive SSI (0% vs. 2.5%, P=0.34), overall complication rate (34% vs. 55%, P=0.008) and overall infection rate (11% vs. 21%, P=0.09). Multivariate analysis demonstrated that the extended AMP regime was associated with a significantly lower risk of overall complication (P