Complicated urinary tract infection (cUTI) occurs in patients with structural or functional urinary tract abnormalities (urinary obstruction, urolithiasis, neurogenic bladder, urinary catheters, recent instrumentation, anatomical anomalies, post-urological surgery, transplant kidney) or systemic conditions associated with treatment failure or progression risk (pregnancy, male sex, diabetes, immunocompromise, healthcare-associated infection, hospital acquisition). Pyelonephritis is generally classified as complicated. Catheter-associated UTI (CAUTI) is the most common healthcare-associated infection, accounting for 35% of nosocomial infections.
Microbiology is more diverse and resistant than uncomplicated UTI: E. coli remains predominant (50-70%) but with higher rates of ESBL, fluoroquinolone resistance, and AmpC; other Enterobacteriaceae (Klebsiella pneumoniae, Enterobacter, Proteus, Citrobacter, Morganella), non-fermenters (Pseudomonas aeruginosa, Acinetobacter), gram-positives (Enterococcus, Staphylococcus aureus including MRSA), and Candida (especially in long-term catheters). MDR organisms (ESBL, CRE, MDR Pseudomonas) are increasing concerns globally.
Diagnosis requires urinalysis (pyuria, leukocyte esterase, nitrite), urine culture (≥10⁵ CFU/mL voided, ≥10² catheter-collected), and blood cultures if febrile/septic. Imaging (CT or ultrasound) is indicated for failure to respond, suspected obstruction, abscess, or pyelonephritis. Empiric antibiotic therapy depends on severity, local resistance patterns, and risk factors: outpatient cUTI/pyelonephritis: ceftriaxone, fluoroquinolone (avoid if local resistance >10%), or aminoglycoside-cephalosporin combination. Hospitalized: piperacillin/tazobactam, ceftazidime/avibactam, or carbapenem (meropenem, ertapenem) for severe sepsis or ESBL risk. MDR concerns: ceftolozane/tazobactam, ceftazidime/avibactam, plazomicin, or polymyxins per susceptibility. Adjuncts: source control (ureteral stent or percutaneous nephrostomy for obstruction, drainage of perinephric/renal abscess, catheter exchange or removal), supportive care (fluids, antipyretics), and de-escalation based on culture results. Duration: 7-14 days; longer for prostatitis (4-6 weeks), abscess (4-6 weeks), or persistent obstruction.