Blood Culture Testing in Fracture-Related Infections: Low Yield and Lack of Concordance with Deep Tissue Pathogens

OBJECTIVES: To assess the concordance between blood culture isolates and intraoperative deep tissue cultures in patients with confirmed fracture-related infection (FRI). METHODS: Design: Retrospective Cohort Study Setting: Academic Medical Center Patient Selection Criteria: This Institutional Review Board-approved study included patients 18 years and older diagnosed with a confirmed FRI according to the FRI Consensus Group criteria who, at time of irrigation and debridement (I&D), underwent deep tissue culture (TC) as well as concurrent blood culture (BC) testing (in the Emergency Department or inpatient setting). The decision to perform BC testing was left to the discretion of the initial treating providers at the time of this presentation. Outcome Measures and Comparisons: Microbiological data were reviewed from the electronic medical record. Infections were classified as monomicrobial (either gram-positive or gram-negative), polymicrobial, or culture negative. Pathogen concordance between blood and intraoperative tissue cultures was analyzed. RESULTS: 84 patients were included with both intraoperative deep TC and concurrent BC. This cohort had a mean age of 56.2 ± 20.3 years and consisted of 33 females (39.3%). BC were never ordered by the orthopedic surgeon. Microbial analysis of deep tissue specimens identified 29 gram-positive infections, 18 gram-negative infections, 33 polymicrobial infections, and 4 culture-negative cases. Of the 84 BC analyzed, 69 (82.1%) were culture-negative and 15 (17.9%) were culture-positive. BC results were discordant with their respective TC isolates in 76 of 84 (90.4%) cases. This discordance in 76 cases was driven by negative BC in the setting of positive TC (69/76, 90.8%), while a smaller proportion reflected growth of different organisms in BC compared to TC (7/76, 9.2%). Concordance was observed in only 8 of 84 (9.6%) cases, in which BC identified at least one pathogen sampled from TC. BC yielded negative culture results 17 times as often as TC. McNemar’s test revealed a highly significant difference in culture-positivity rates (χ2=65, p <0.0001), while Cohen’s Kappa for agreement was 0.022, indicating minimal agreement between BC and TC results. CONCLUSIONS: These results suggest that blood cultures were part of some workflows for patients presenting with infections, but they did not reflect the true bony pathogens nor contribute meaningful diagnostic information in most cases of confirmed fracture-related infection (FRI) according to the FRI Consensus Group criteria. While blood culture testing is important in the evaluation of systemic infection from, it does not provide orthopedic surgeons with information that informs the management or treatment of the FRI itself. LEVEL OF EVIDENCE: III