Microbiologic profile of infections in presumed aseptic revision spine surgery.

PURPOSE: Intra-operative cultures may be obtained in revision spine surgery despite the absence of pre-operative clinical markers of infection. The microbiologic profile of culture positive cases in which there is no clear evidence of infection preoperatively has not been described. The aim of this investigation is to report on the microbiologic profile of unexpected culture positive revision spine surgery cases. METHODS: We retrospectively reviewed 595 consecutive revision spine surgeries performed between 2008 and 2013. Five hundred and seventy-eight revision surgeries were performed for diagnoses other than infection and were included in the study. RESULTS: Operative cultures were obtained in 112 cases (19.4 %). Cultures were positive in 45 cases. Pseudarthrosis was not only the most common diagnosis overall (49.1 %) in which intra-operative cultures were obtained, it was also the most common revision surgical diagnosis where cultures were positive (55.6 %). Propionibacterium acnes was cultured in 54.2 % of cases with the primary diagnosis of pseudarthrosis, but only in 40.9 % of cases with other diagnoses (P = 0.554). Overall, staphylococcal species were found most commonly (57.8 % of cases), but P. acnes was at least one of the isolates in 48.9 % of cases and was three times more common than any other organism. CONCLUSIONS: Nearly one in five patients with the diagnosis of pseudarthrosis were culture positive. More specifically, pseudarthrosis was the most common culture positive diagnosis and P. acnes species predominated in this patient population. Propionibacterium acnes was overwhelmingly the most common single organism cultured in revision spine surgery. Given this, we recommend all cultures be held for P. acnes, particularly in the setting of pseudarthrosis.