Abstract
Background:The purpose of this study was to describe the culture and speciation results of patients with surgical site infection (SSI) from the PREPARE and Aqueous-PREP studies from the PREP-IT Investigators. Methods:Patients with suspected SSI underwent collection of deep or organ tissue samples for culture. The culture positivity rate was estimated as a percentage along with the exact binomial 95% confidence interval (CI). Microbial species were reported as percentages. Comparisons between open and closed fractures were conducted with the Z-test for proportions. Significance was set at p < 0.05. Results:Among the 2 primary studies, a total of 484 cases (defined as an anatomic fracture area; some patients had multiple fractures, which were each defined as a case if they developed an infection) had culture samples taken from deep or organ tissue. The culture positivity rate was 96.7% (95% CI, 94.7% to 98.0% [468 of 484 cases]). There were no significant differences (p = 0.507) in culture positivity between open fractures (97.2% [95% CI, 94.5% to 98.6%]; 273 of 281 cases) and closed fractures (96.1% [95% CI, 92.4% to 98.0%]; 195 of 203 cases). There was information on microbial species in 84.4% (395) of 468 cases. For patients with positive cultures, 43.3% (171 of 395 cases) were polymicrobial infections. Open fractures (47.8% [111 of 232 cases]), compared with closed fractures (36.8% [60 of 163 cases]), were more likely to be polymicrobial (p = 0.029). Staphylococcus aureus microbes (methicillin-sensitive S. aureus, methicillin-resistant S. aureus, and coagulase-negative S. aureus) accounted for 43.3% (462 of 1,066) of all positive cultures. The median time to infection was 58.5 days (95% CI, 49.0 to 67.0 days). The median time to infection was not significantly different in cases of open fractures (61.0 days [95% CI, 51.0 to 71.0 days]) compared with closed fractures (54.0 days [95% CI, 43.0 to 67.0 days]) (hazard ratio [HR], 0.92 [95% CI, 0.72 to 1.12]). SSIs associated with gram-negative bacteria had a shorter median time to infection at 46.0 days (95% CI, 36.0 to 58.0 days) compared with SSIs not associated with gram-negative bacteria at 70.0 days (95% CI, 56.0 to 88.0 days) (HR, 1.79 [95% CI, 1.55 to 2.03]). There was also a shorter median time to infection for patients with polymicrobial infections (47.0 days [95% CI, 38.8 to 52.1 days]) compared with patients with monomicrobial infections (78.6 days [95% CI, 57.2 to 86.8 days]) (HR, 1.26 [95% CI, 1.03 to 1.49]). Conclusions:In patients with SSI, tissue samples yielded high rates of microbial culture results. There was a higher proportion of gram-negative organisms in open fractures. Gram-negative infections were also associated with earlier time to infection. Clinicians should not hesitate to take deep-tissue culture samples in patients with suspected SSI and should be prepared to encounter polymicrobial infections. Level of Evidence:Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.