Urinary Tract Infection - Complicated

Definition

Complicated urinary tract infection (UTI) refers to infections of the urinary tract associated with structural or functional abnormalities of the urinary system, comorbidities, or resistant pathogens, leading to higher risk of treatment failure and complications.

Epidemiology

• More common in adults with underlying urinary tract abnormalities, catheter use, diabetes, or immunosuppression.
• Higher prevalence in hospitalized patients and those with recent urological procedures.
• Incidence increases with age, particularly in men over 50 due to prostatic enlargement.
• Risk factors: urinary obstruction, stones, neurogenic bladder, indwelling catheters, pregnancy, chronic kidney disease.

Etiology

• Most common pathogen: *Escherichia coli* (often resistant strains).
• Other pathogens: *Klebsiella*, *Proteus*, *Pseudomonas*, *Enterococcus*, *Staphylococcus saprophyticus* (less common in complicated UTI).
• Polymicrobial infections possible, especially in catheter-associated UTIs.
• Risk factors: urinary stasis, instrumentation, prior antibiotic use, immunosuppression.

Pathophysiology

• Pathogens ascend from urethra to bladder and sometimes kidneys.
• Urinary tract abnormalities (obstruction, stones) promote bacterial colonization and biofilm formation.
• Inflammatory response: cytokine release, neutrophil infiltration, and urothelial damage.
• In severe cases, infection can progress to pyelonephritis, bacteremia, or urosepsis.