Deep Infections After Open and Closed Fractures

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.

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.

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]).

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.

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.