Allogenic bone grafts and postoperative surgical site infection: are positive intraoperative swab cultures predictive for a higher infectious risk?

In spine surgery, allogenic bone grafts are often required to ensure bone fusion, however, the main concern regarding their use is the infection risk: therefore, an intraoperative swab for culture test is performed. The cost-effectiveness of these swabs and their influence on the patients' postoperative course have often been questioned. This study aims at determining whether positive spine allograft culture results are predictive of an increased risk of surgical site infection and whether they influence the surgeon's choices in postoperative management. The records of 340 patients who received allogenic bone graft during spinal fusion surgery in our institution were reviewed, for a total of 677 allografts. Each graft was swabbed intraoperatively. All patients were followed clinically for postoperative complications. Infection was diagnosed based on clinical data, blood tests and radiographic images, all assessed by an infectious disease specialist. Only 4 of the 677 allografts used (0.6%) resulted positive at the intraoperative swab culture. Three cultures were positive for Staphylococcus epidermidis and one culture for S. warneri. No clinical infection occurred in any of these patients. Twenty-eight of the 340 patients (8.2%) developed an infection, but none of them had a positive intraoperative swab culture. The most common microbiologic pathogen isolated from this cohort was S. aureus. According to our series, intraoperative swab culture results were not predictive for higher risk of infection and did not affect the clinical behavior of the surgeons in postoperative management.