Risk Factors for Surgical Site Infections Following Spinal Fusion Procedures: A Case-Control Study

Background. Spinal fusion procedures are associated with a significant rate of surgical site infection (SSI) (1%-12%). The goal of this study was to identify modifiable risk factors for spinal fusion SSIs at a large tertiary care center. Methods. A retrospective, case-control (1:3 ratio) analysis of SSIs following posterior spine fusion procedures was performed over a 1-year period. Clinical and surgical data were collected through electronic database and chart review. Variables were evaluated by univariate analysis and multivariable logistic regression. Results. In total, 57 deep SSIs were identified out of 1587 procedures (3.6%). Infections were diagnosed a mean of 13.5 +/- 6 8 days postprocedure. Staphylococcus aureus was the predominant pathogen (63%); 1/3 of these isolates were methicillin resistant. Significant patient risk factors for infection by univariate analysis included ASA score >2 and male gender. Among surgical variables, infected cases had significantly higher proportions of staged procedures and thoracic level surgeries and had a greater number of vertebrae fused. Notably, infected fusion procedures had a longer duration of closed suction drains than controls (5.1 +/- 6 2 days vs 3.4 +/- 6 1 day, respectively; P< .001). Drain duration (unit odds ratio [OR], 1.6 per day drain present; 95% confidence interval [CI], 1.3-1.9), body mass index (OR, 1.1; 95% CI, 1.0-1.1), and male gender (OR, 2.7; 95% CI, 1.4-5.6) were significant risk factors in the multivariate analysis. Conclusions. Prolonged duration of closed suction drains is a strong independent risk factor for SSI following instrumented spinal fusion procedures. Therefore, removing drains as early as possible may lower infection rates.