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Urinary tract infections (UTIs) are bacterial infections affecting any part of the urinary system, most commonly the bladder (cystitis) and urethra (urethritis). Pyelonephritis represents a more severe upper urinary tract infection involving the kidneys and renal pelvis, often resulting from ascending lower UTI or hematogenous spread.
UTIs typically result from bacterial ascension through the urethra, with E. coli being the most common pathogen (80-85% of cases). The shorter female urethra and proximity to anal opening increase infection risk, while host factors like urinary stasis, immunosuppression, and structural abnormalities facilitate bacterial adherence and proliferation. Pyelonephritis occurs when bacteria ascend from the lower urinary tract to the renal parenchyma, triggering inflammatory responses that can lead to scarring and reduced kidney function if untreated.
Lower UTI symptoms include dysuria, frequency, urgency, and suprapubic pain, while pyelonephritis presents with fever, chills, flank pain, and systemic toxicity in addition to urinary symptoms. Diagnosis relies on urinalysis showing pyuria, bacteriuria, and positive nitrites/leukocyte esterase, confirmed by urine culture with >10^5 CFU/mL. Treatment involves appropriate antibiotic selection based on local resistance patterns, with fluoroquinolones or trimethoprim-sulfamethoxazole for uncomplicated cystitis, while pyelonephritis requires broader spectrum antibiotics and often hospitalization for severe cases.
Key imaging focus: Wedge-shaped hypoperfusion, perinephric stranding, abscess, obstructing stone