Thursday, April 10, 2014
Vancomycin Powder and the Microbiology of Surgical Site Infection
Level 2 studies have shown that subfascial vancomycin powder is effective in reducing surgical site infections in posterior fusions in the cervical, thoracic, and lumbar spine, with the most pronounced benefit observed in high risk trauma patients. While vancomycin powder likely reduces the rate of surgical site infection, it does not eradicate the problem, and there is concern that its use could alter the microbiology observed when infection does occur. In an attempt to determine the effect of subfascial vancomycin powder on the microbiological spectrum of surgical site infection, Dr. Prasad and his colleagues from Philadelphia reviewed 981 consecutive spine surgery patients treated with vancomycin powder to evaluate the microbiology of surgical site infection in this population. They defined deep infection as the presence of clinical signs and symptoms consistent with surgical site infection leading to a return to the OR for irrigation and debridement, regardless of culture results. Based on this definition, 6.7% of patients had a surgical site infection, and 5.2% had positive wound cultures. Consistent with prior studies, 86% of patients with positive cultures were infected with gram positive organisms, the majority of which were Staph aureus. However, 60% of patients also had gram negative organisms grow from intra-operative cultures, compared to a historical control of 21% at the same institution. Based on these findings, the authors concluded that vancomycin powder could increase the rate of gram negative or polymicrobial infection.
This paper is the first large study to look in-depth at the microbiology of surgical site infection following the application of subfascial vancomycin powder. The data do indicate a markedly increased rate of gram negative infection compared to historical controls. However, the historical controls also had a lower overall rate of infection. This indicates that the historical controls were likely a very different population compared to patients in the current study, who received vancomycin based on surgeon choice. Approximately 90% of patients in the current study underwent fusion, while at least 20% of the patients in the historical controls underwent decompression alone. Given the likely difference in the two populations, it is hard to know if the use of vancomycin powder was driving the higher rate of gram negative infection or if patients receiving vancomycin were at higher risk of gram negative and polymicrobial infection. It is interesting that the proportion of patients with gram positive infection remained about the same despite the use of vancomycin. This paper makes an important contribution and should alert clinicians to the possibility of gram negative infection following the use of vancomycin powder. In patients who have received vancomycin powder and present with a surgical site infection, empirical broad spectrum antibiotics should be considered until culture data are back.
Please read Dr. Prasad’s article on this topic in the April 1 issue. Does this change your view on the use of subfascial vancomycin powder? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor