Bacteriology and Risk Factors for Development of Late (Greater Than One Year) Deep Infection Following Spinal Fusion With Instrumentation.

Study Design: Retrospective cohort review.
Objectives: To evaluate patients who underwent instrumented spinal fusion procedures and compare late (more than 1 year) and early infection (less than 1 year).
Summary of Background Data: Centers for Disease Control and Prevention criteria for surgical site infections with implants include infections occurring at less than 1 year postoperatively. The authors observed a high rate of deep infection at more 1 year after instrumented spinal fusion. Retrospective review was conducted to determine whether differences in bacteriology, patient demographics, or surgical factors exist between late and early infection.
Methods: A total of 1,390 patients underwent spinal fusion with instrumentation from 2000 to 2009. Deep infection requiring operative debridement occurred in 112 patients (70 at less than 1 year and 42 at more than 1 year after the index surgery). Clinical, operative, and microbiology reports were reviewed and logistic regression was performed to evaluate the relationship between these factors and time of infection.
Results: The most common organisms in the greater than 1 year group were Propionibacterium acnes, compared with Staphylococcus aureus in the less than 1 year group. The odds of late infection in the P acnes group were 15.5 (95% confidence interval [CI], 4.36-54.72) times the odds among all other organisms (p < .0001). Patient demographics and surgical factors were not different between groups. Among all patients, the infection rate was significantly higher in patients who received stainless-steel implants (11.56%) compared with those who received titanium implants (3.53%) (p < .0001). In univariate analysis, the odds of late infection in the stainless-steel group were 6.09 (95% CI, 1.62-39.88) times the odds in the titanium group (p = .0042). However, in multivariate analysis, controlling for organism type reduced the odds ratio to 4.62 (95% CI, .53-40.14), with only a trend to significance (p = .1656).
Conclusions: Propionibacterium acnes was more commonly identified in late infection. Patients with stainless-steel implants had a higher incidence of late infection than those with titanium implants, but this was not significant after controlling for organism type.
(Copyright © 2014 Scoliosis Research Society. Published by Elsevier Inc. All rights reserved.)