Urinary Tract Infections

Overview – Urinary Tract Infections

Urinary tract infections (UTIs) are among the most common bacterial infections encountered in clinical practice. Cystitis refers specifically to bladder inflammation due to infection. UTIs are usually caused by ascending infections with Escherichia coli, and are particularly common in women due to anatomical factors. Clinical features range from dysuria and frequency in adults to non-specific signs like irritability in infants and confusion in the elderly. Prompt recognition and treatment are essential to prevent complications like pyelonephritis or urosepsis. This guide provides a high-yield summary for final-year medical students.

Definition

A urinary tract infection (UTI) is an infection of any part of the urinary system, most commonly involving the bladder (cystitis) and urethra. It is typically bacterial in origin.

Aetiology

• Bacterial infections (most common)
  • Escherichia coli – most frequent causative agent
  • Staphylococcus saprophyticus – especially in sexually active women
• Fungal infections – less common, seen in immunocompromised or catheterised patients

Risk Factors

• Urinary incontinence
• Indwelling urinary catheter
• Female sex (shorter urethra facilitates ascending infection)
• Sexual intercourse
• Diabetes mellitus

Pathogenesis

Ascending Infection (most common)

• Bacteria from perineum/rectum ascend → urethra → bladder → potentially kidneys

Descending Infection

• Haematogenous or lymphatic spread from systemic infection → kidneys → bladder

Clinical Features

• Suprapubic pain
• Dysuria
• Increased urinary frequency and urgency
• Small volume urine voids

Atypical Presentations

• Infants: fever, irritability, poor feeding
• Elderly: fatigue, incontinence, altered mental status (delirium)

Investigations

• Urine microscopy, culture, and sensitivity (MC&S)
  • Presence of bacteria
  • Nitrites (indicate Gram-negative bacteria)
  • Leukocyte esterase
  • Pyuria (WBCs in urine)
  • Haematuria (occasionally)

Management

Antibiotic Therapy

• Common first-line agents:
  • Trimethoprim–sulfamethoxazole
  • Ciprofloxacin
  • Ceftriaxone
  • Azithromycin
  • Penicillin-based options depending on resistance profile

Supportive Measures

• Encourage increased oral fluid intake
• Address or minimise risk factors (e.g., remove unnecessary catheters)

Complications

• Pyelonephritis – if infection ascends to kidneys
• Urosepsis – systemic infection that may result in septic shock

Differential Diagnosis

• Vaginitis
• Urethritis (e.g. chlamydia or gonorrhoea)
• Interstitial cystitis
• Pelvic inflammatory disease
• Prostatitis (in males)

Summary – Urinary Tract Infections

Urinary tract infections are common infections typically caused by E. coli and frequently present with dysuria, urgency, and suprapubic pain. Atypical presentations occur in the very young and elderly. Diagnosis is confirmed with urine microscopy, culture, and sensitivity, and treatment includes antibiotics and risk factor modification. For a broader context, see our Renal Overview page.