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Published on: October 15, 2014
Blood Culture Testing in Fracture-related Infections: Low Yield and Lack of Concordance With Deep Tissue Pathogens
Lauren A Merrell1, Sara J Solasz1, Abhishek Ganta1,2
1Division of Orthopedic Trauma SurgeryNYU Langone Health, NYU Langone Orthopedic Hospital, New York, NY; and.
Objectives:
To assess the concordance between blood culture isolates and intraoperative deep tissue cultures in patients with confirmed fracture-related infection (FRI).
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 the 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:
Eighty four 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 women (39.3%). BC were never ordered by the orthopaedic 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 cases (90.4%). 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 with TC (7/76, 9.2%). Concordance was observed in only 8 of 84 cases (9.6%), in which BC identified at least 1 pathogen sampled from TC. BC yielded negative culture results 17 times as often as TC. The McNemar test revealed a highly significant difference in culture-positivity rates (χ 2 = 65, P < 0.0001), while Cohen 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 orthopaedic surgeons with information that informs the management or treatment of the FRI itself.
Level Of Evidence:
Diagnostic, LoE III. See Instructions for Authors for a complete description of levels of evidence.
Insights
Blood cultures rarely identify pathogens in fracture-related infections (FRI). Intraoperative tissue cultures are more effective for diagnosing FRI, as blood cultures showed minimal agreement and diagnostic value for orthopedic surgeons.
Area of Science:
- Orthopedics
- Infectious Diseases
- Medical Microbiology
Background:
- Fracture-related infections (FRI) are serious complications requiring accurate diagnosis.
- Blood cultures (BC) are often used in infection workups, but their utility in FRI is unclear.
- Intraoperative deep tissue cultures (TC) are considered a gold standard for diagnosing bone infections.
Purpose of the Study:
- To evaluate the concordance between blood cultures (BC) and intraoperative deep tissue cultures (TC) in patients with confirmed fracture-related infections (FRI).
- To determine the diagnostic value of BC for orthopedic surgeons managing FRI.
Main Methods:
- Retrospective cohort study of 84 patients with confirmed FRI.
- Concurrent BC and deep TC were collected during irrigation and debridement (I&D).
- Microbiological data were analyzed for pathogen concordance and culture results.
Main Results:
- Only 9.6% of BC results were concordant with TC isolates.
- BC were negative in 82.1% of cases, compared to TC.
- BC showed minimal agreement (Cohen's Kappa = 0.022) with TC, with 90.4% discordance.
Conclusions:
- Blood cultures provided limited diagnostic information for managing FRI.
- Intraoperative deep tissue cultures are more reliable for identifying pathogens in FRI.
- BC are not recommended for guiding the management of fracture-related infections.
