Enterobacter sp. is a gram-negative, often drug-resistant bacillus that is classically identified from mucosal surfaces such as pulmonary or urinary tracts. Despite its virulence, Enterobacter represents a less common pathogen in prosthetic joint infections (PJI). This study aims to resolve the current paucity of described clinical characteristics and treatment success of Enterobacter PJI.
Thirty-three patients with Enterobacter aerogenes-, cloaecae/asburiae-, or hormachei-positive PJIs were identified at a single institution. Infection clearance was defined as absence of infection or repeat surgery at one year and off all adjunct antibiotic therapy. The primary survival outcome is no additional surgery or antibiotic treatment, and the secondary outcome is no additional surgery for reinfection or antibiotic treatment. Patient demographics, PJI characteristics, treatments, and clinical outcomes were compared between patients with and without clearance. Chi-squared statistics or Fisher’s exact tests were run for categorical variables, and ANOVA and Kruskal-Wallis tests were run for continuous variables comparing multiple index procedures. Multivariable logistic regression models were analyzed to derive odds ratios and 95% confidence intervals. Survival analyses and Kaplan-Meier survival curves were run for primary and secondary survival outcomes. Tests for statistical significance were set to alpha=0.05.
The mean age of the cohort was 66.8 years (SD: 11.6), 18 subjects were male (54.5%), mean BMI was 31.0 (SD: 7.1), and mean Elixhauser Comorbidity Score was 9.1 (SD: 4.5). Mean time to PJI diagnosis after surgery was 21 days [IQR: 17-55]. Most subjects had a prior PJI (n=18, 54.5%) and multiple prior surgeries (n=29, 87.9%) in the same joint. Index procedures were debridement, antibiotics, and implant retention (DAIR) in 33.3% (n=11), 2-stage reimplantation in 36.4% (n=12), and resection arthroplasty or amputation in 30.3% (n=10). Time to reinfection was significantly longer for subjects with index 2-stage as compared to those with index DAIR (p=0.028). With a median follow-up of 2.9 years, final joint outcomes included retained prosthetic in 5 (15.2%), reimplantation in 5 (15.2%), destination spacer in 5 (15.2%), arthrodesis in 2 (6.1%), resection arthroplasty in 9 (27.3%), and above-knee amputation in 7 (21.2%).
Enterobacter PJI often presents acutely and is difficult to treat with high rates of failure and ultimate joint- or limb-sacrificing procedure. Despite being a less common cause of PJI, prognosis is exceptionally poor with traditional treatment algorithms when compared to historical cohorts of more common pathogens.