What is a Urinary Tract Infection (UTI)?

What is a Urinary Tract Infection (UTI)?

A urinary tract infection (UTI) is an infection of the urinary system causing an inflammatory response that occurs when normal flora of the periurethral area are replaced by uropathogenic bacteria, which ascend through the urinary tract, most commonly causing bacterial cystitis and less frequently progressing to the kidneys causing pyelonephritis. 1

Definition and Pathophysiology

• UTIs develop when uropathogenic bacteria replace the normal periurethral flora and ascend through the urinary tract, causing inflammation 1
• The infection typically begins as bacterial cystitis (bladder infection) and may progress to involve the kidneys (pyelonephritis) in some cases 1
• A clean-catch or catheterized urine specimen for culture typically reveals >100,000 organisms per milliliter of urine in patients with UTI 1

Common Causative Organisms

• Escherichia coli is the most common pathogen, causing approximately 75% of UTIs 1
• Other common pathogens include Enterococcus faecalis, Proteus mirabilis, Klebsiella species, and Staphylococcus saprophyticus 1, 2
• Less common pathogens include Pseudomonas aeruginosa, Enterobacter species, and Candida species 2

Classification of UTIs

Uncomplicated UTI

• Occurs in patients without structural or functional abnormalities of the urinary tract and without relevant comorbidities 1
• Includes both lower tract infection (cystitis) and upper tract infection (pyelonephritis) 1
• Typically responds well to appropriate antimicrobial therapy 1

Complicated UTI

• Occurs in patients with underlying structural or medical problems 1
• Associated factors include anatomical abnormalities (cystoceles, diverticula, fistulae), indwelling catheters, urinary tract obstruction, and conditions such as pregnancy, diabetes, and immunosuppression 1
• Other risk factors include prior urinary tract surgery/trauma, gross hematuria after infection resolution, prior urinary calculi, and symptoms of pneumaturia or fecaluria 1

Recurrent UTI

• Defined as at least three episodes of infection within the preceding 12 months 1
• May involve reinfection from an external source or bacterial persistence 1
• Often related to sexual habits and hygiene, especially in sexually active women using diaphragms or spermicides 1

Common Symptoms

• Lower UTI (cystitis): dysuria, urinary frequency, urgency, nocturia, and suprapubic pain 3
• Upper UTI (pyelonephritis): systemic symptoms including high fever, malaise, vomiting, and flank pain/tenderness 1
• In older adults, symptoms may be atypical and include confusion, altered mental status, or functional decline 1

Risk Factors

• Female sex (lifetime risk >50% for women) 1
• Sexual activity, especially with use of diaphragms or spermicides 1
• History of prior UTI 2
• Urinary catheterization (3-8% risk of bacteriuria per day of catheterization) 1
• Anatomical or functional abnormalities of the urinary tract 1
• In postmenopausal women: urinary incontinence, cystocele, or high postvoid residual urine 1

Diagnostic Approach

• Diagnosis typically based on symptoms and confirmed with urine analysis or culture 4
• In women with typical symptoms (frequency, urgency, dysuria) without vaginal discharge, self-diagnosis is often accurate enough without further testing 3
• Urine culture should be reserved for complicated cases, recurrent infections, treatment failures, or atypical presentations 3

Treatment Considerations

• First-line antibiotics for uncomplicated UTI include nitrofurantoin, fosfomycin, trimethoprim, or trimethoprim/sulfamethoxazole 3
• Treatment duration varies from single-dose to 7-14 days depending on the specific antibiotic and patient factors 1
• For complicated UTIs, treatment should be based on local antimicrobial sensitivity patterns and adjusted according to culture results 1
• Self-care measures for prevention include adequate hydration, urge-initiated voiding, post-coital voiding, and avoiding spermicide-containing contraceptives 1

Special Populations

• Men with UTI symptoms should always receive antibiotics with treatment guided by urine culture 3
• Catheter-associated UTIs require removal or replacement of the catheter before starting antimicrobial therapy 1
• In older adults, diagnosis may be challenging due to atypical presentations, requiring a more holistic assessment 1