2021 Young Investigator Award Winner: Anatomic Gradients in the Microbiology of Spinal Fusion Surgical Site Infection and Resistance to Surgical Antimicrobial Prophylaxis

Abstract

Study Design. Retrospective hospital-registry study. Objective. To characterize the microbial epidemiology of surgical site infection (SSI) in spinal fusion surgery and the burden of resistance to standard surgical antibiotic prophylaxis. Summary of Background Data. SSI persists as a leading complication of spinal fusion surgery despite the growth of enhanced recovery programs and improvements in other measures of surgical quality. Improved understandings of SSI microbiology and common mechanisms of failure for current prevention strategies are required to inform the development of novel approaches to prevention relevant to modern surgical practice. Methods. Spinal fusion cases performed at a single referral center between January 2011 and June 2019 were reviewed and SSI cases meeting National Healthcare Safety Network criteria were identified. Using microbiologic and procedural data from each case, we analyzed the anatomic distribution of pathogens, their differential time to presentation, and correlation with methicillin-resistant Staphylococcus aureus screening results. Susceptibility of isolates cultured from each infection were compared with the spectrum of surgical antibiotic prophylaxis administered during the index procedure on a per-case basis. Susceptibility to alternate prophylactic agents was also modeled. Results. Among 6727 cases, 351 infections occurred within 90 days. An anatomic gradient in the microbiology of SSI was observed across the length of the back, transitioning from cutaneous (gram-positive) flora in the cervical spine to enteric (gram-negative/anaerobic) flora in the lumbosacral region (correlation coefficient 0.94, P < 0.001). The majority (57.5%) of infections were resistant to the prophylaxis administered during the procedure. Cephalosporin-resistant gram-negative infection was common at lumbosacral levels and undetected methicillin-resistance was common at cervical levels. Conclusion. Individualized infection prevention strategies tailored to operative level are needed in spine surgery. Endogenous wound contamination with enteric flora may be a common mechanism of infection in lumbosacral fusion. Novel approaches to prophylaxis and prevention should be prioritized in this population. Level of Evidence: 3

Does Post-Operative Spine Infection Bacterial Gram Type Affect Surgical Debridement or Antibiotic Duration?

“…When examining the relationship between anatomic region and the microbiology of SSI following spinal fusions, patients who were found to have mixed infections were more likely to have undergone thoracic fusion, while patients who had gram-positive and gram-negative infections were more likely to have undergone cervical and lumbar fusion, respectively. This finding is consistent with previous studies, with 2 retrospective studies reporting greater proportions of gram-positive infections occurring after cervical fusions, while gram-negative infections followed lumbar/lumbosacral fusion 10,11. A likely explanation for this finding is due to the natural microbiome of the skin and intestinal tract; gram-positive species are among the most common skin flora, while gram-negative species are among the most common intestinal flora, frequently identified near the lumbosacral region 18,19.…”

The efficacy of bactrim in reducing surgical site infections after spine surgery

“…In a similar study by Long, et al, the authors performed a retrospective review on 6727 patients. 11 The authors noted that Cephalosporin-resistant gram-negative infection was common at lumbosacral levels. And the authors suggested "novel approaches to prophylaxis and prevention should be prioritized in this population".…”

“…These authors noted “ gram-negative organisms accounted for a sizeable portion of SSI, particularly among lower lumbar and sacral spine surgical procedures”. In a similar study by Long, et al, the authors performed a retrospective review on 6727 patients [11] . The authors noted that Cephalosporin-resistant gram-negative infection was common at lumbosacral levels.…”

“…This regimen is very good for gram-positive organisms, but it does not provide adequate coverage for gram-negative organisms. [9][10][11] Bactrim (sulfamethoxazole/trimethoprim) is a very effective and popular treatment for gram-negative and MRSA infections. Therefore, Bactrim has been studied as a post-operative prophylactic oral antibiotic regime in multiple surgical specialties, such as vascular, colorectal, and neurosurgery.…”

“…Clindamycin is generally used when patients are unable to have a first generation Cephalosporin because of allergies. This regimen is very good for gram-positive organisms, but it does not provide adequate coverage for gram-negative organisms [9] , [10] , [11] .…”