Recurrent Failures After 2-Stage Exchanges are Secondary to New Organisms Not Previously Covered by Antibiotics.

Background: Prior studies have shown that the majority of re-infections following two-stage revisions are due to organisms different from the initial organisms identified. It remains unknown whether these new organisms were susceptible to the antibiotics given (indicating the patient likely developed another infection following successful treatment) or not susceptible (indicating these organisms may have been initially present, but were not identified, and thus, inadequately treated). The purpose of this study was to determine if bacteria identified at time of re-infection following two-stage revisions were susceptible to the antibiotics administered during treatment of the index infection, in order to understand if these are new infections or from organisms that were present but not initially identified. Methods: Thirty failures (19 knees and 11 hips) following two-stage revisions from four institutions were identified. Cultures and antibiotic sensitivities were used to determine whether the re-infectious organisms were new and if they were susceptible to the antibiotics initially given. Results: Twenty-five (83.3%) re-infections were due to new organisms. Of these re-infections from new organisms, 16 (64.0%) were susceptible to the antibiotics previously administered, suggesting they were new infections rather than persistent infections from organisms that were not detected during initial treatment. No statistically significant differences in demographics or time to revision were observed when comparing by organism type (new vs. repeat) or by antibiotic susceptibility. Conclusions: Failures following two-stage revisions are frequently due to organisms different than those identified prior to two-stage revision and are likely new infections rather than persistent infections from undetected organisms.