900 - Retrospective Review of Microbiological profile in Post Surgical Spine Infections and Assess the Appropriateness of Current Pre-Op Antibiotic Prophylaxis Policy

Background: SSI is a devastating complication of spine surgery that results in significant morbidity as it requires prolonged antibiotic courses and multiple surgical debridements. It also increases the economic burden on the health care system. So, it becomes important to learn the microbiological profile and assess the current pro-op antibiotic prophylaxis policy.

Methods: All cases reported by the hospital infection control surveillance program based on CDC/NHSN Surveillance definitions between January 2017 and July 2019 were retrospectively reviewed for microbiological data and surgical characteristics using electronic medical record, and non-parametric test was used to assess the difference in proportional distribution of gram-negative organisms between upper and lower spine groups. 

Results: Between January 2017 and July 2019, 3561 spine surgeries were performed, 51 cases of SSI were reported, and 50 patients have microbiological data available. The most commonly isolated organism was Staphylococcus aureus (38%), followed by Escherichia coli (12%). There was no statistical difference for the distribution of gram-negative organisms in upper spine (17) and lower spine (33) surgeries (29.4% vs 48.4%, P Value = 0.24). However total gram-negative organisms accounted for 42% cases and lower spine surgical procedures were more likely to be associated with mixed infections including both gram negative and gram-positive organisms (15.1% vs 0%). Cefazolin resistant gram-negative organisms accounted for 22% of all gram-negative infections. Our current pre-op antibiotic policy recommends cefazolin plus or minus vancomycin (If MRSA screen positive) and clindamycin plus vancomycin in patients with severe penicillin allergy.Table 1: Characteristics of the cultures
Table: 2 Microorganisms isolated from 50 patients with post-surgical spine infections
Figure 1: Proportional distribution of Micro-organisms between lower and upper spine (Percentage on left side and No. of positive cultures on right side)


Conclusion: Although gram-positive organism predominated, there was a substantial portion of gram-negative organisms in post-surgical spine infections. Cefazolin would cover at least half of the gram-negative organisms identified based on our antibiogram susceptibility pattern. However, in patients with penicillin allergy, our current recommended pre-operative antibiotic prophylaxis does not provide gram-negative coverage.  We will therefore explore the value of adding an agent with gram negative coverage based on our institutional antibiogram.