Prolonged Suppression of Bacterial Growth in Urine Culture Following Fluoroquinolone Therapy in an Elderly Diabetic Patient: A Diagnostic Pitfall

Urine culture is the gold standard for diagnosing urinary tract infections (UTIs), but prior antibiotic therapy can cause false-negative results. Fluoroquinolones (FQs), commonly used for complicated UTIs, may cause prolonged post-antibiotic effect (PAE), particularly in high-risk patients. We report an 81-year-old diabetic woman with persistent urinary symptoms who received empirical levofloxacin (LFX) therapy. Despite adherence to treatment and repeated urine cultures showing bacteriuria on microscopy, urine cultures remained negative for 10 days following antibiotic discontinuation, and subsequently became positive for FQ-resistant Escherichia coli . Renal ultrasonography revealed incidental simple cysts without obstruction or acute pathology. This case highlights a diagnostic pitfall of prolonged suppression of bacterial growth in urine cultures following FQ therapy. This effect may be more pronounced in elderly patients with comorbidities. Clinicians should interpret urine cultures cautiously after FQ use in high-risk patients, and consider repeat sampling when clinical suspicion persists. As a single-case report, the findings may not be generalizable to broader patient populations and should be interpreted with caution.