Authors: Chase Arrington; Kelsey Bouwman; Dorothy Williams
Background: Urinary tract infections (UTIs) account for 30-32% of all healthcare-acquired infections, with Enterococcus species found in 15.9% of all catheter-associated UTIs. Standard treatment options include aminopenicillins, fosfomycin, nitrofurantoin, daptomycin, or vancomycin; however, resistance rates to these continue to climb. Linezolid offers an appealing alternative, but its ability to concentrate within the bladder could limit its clinical utility for UTIs. The manufacturer reports that approximately only 30% of the dose is excreted within the urine. Few retrospective studies exist looking at linezolid's effectiveness in UTIs, but the available data shows similar outcomes regarding clinical success. This study was conducted to assess linezolid’s effectiveness within lower UTIs caused by Enterococcus species in comparison to standard therapies.
Methods: This is a single system, retrospective cohort study assessing linezolid's effectiveness in UTIs caused by Enterococcus species. The study included patients admitted between August 15, 2022, and August 15, 2025. Patients were included if they were 18 years or older, had a positive urine culture reporting an Enterococcus species, and it was their first encounter within the timeframe of this study. Patients were excluded if they had polymicrobial infections, negative urinalysis (<10 white blood cells per high-power field or leukocyte esterase negative), positive blood cultures, received fewer than three days of effective therapy, were pregnant or incarcerated, received both linezolid and another active antibiotic, or had been diagnosed with pyelonephritis. The primary outcome was a composite of bacterial persistence or antibiotic reinitiation within 14 days. Secondary outcomes included length of stay, 30-day recurrence or readmission related to UTI, development of resistance to linezolid, and mortality.
Results: A total of 128 patients were included, with 37 receiving linezolid and 91 receiving conventional therapy. For the primary outcome of bacterial persistence or antibiotic reinitiation, no significant difference was found between linezolid and conventional therapy (13.51% vs. 9.89%, p=0.545). No differences were observed between groups in the secondary outcomes of 30-day UTI readmission rate (24.32% vs. 15.38%, p=0.309), median length of stay (5.83 vs 6.76 days, p=0.592), or 30-day mortality (2.70% vs 8.79%, p=0.446). No patients developed resistance to linezolid within 30 days. Rates of thrombocytopenia during treatment were also comparable between groups (2.70% vs. 3.30%, p=1).
Conclusion: In this retrospective cohort study, linezolid demonstrated comparable outcomes and safety to conventional therapies for the treatment of Enterococcus UTIs. This supports the potential utility of linezolid in UTIs despite concerns regarding urinary drug concentrations, particularly in cases involving resistant Enterococcus species. Larger randomized controlled studies are needed to confirm the findings seen within this study.
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