Urinary Tract Infections (UTIs) – Causes, Types, and Risk Factors

Categories of UTIs based on Location:

• Cystitis: Infection of the bladder.
• Urethritis: Infection of the urethra.
• Pyelonephritis: Infection of the kidneys (upper urinary tract).

Pathogenesis and Spread:

• Most often caused by Escherichia coli (E. coli), which normally reside in the large intestine.
• E. coli ascends through the urethra to infect the bladder (cystitis) or up further into the ureters and kidneys (pyelonephritis).

Pathways of Infection:

• Infection from bacteria in feces:
  • Females are advised to wipe front to back to prevent bacteria from spreading from the anus to the urethra.
  • Females are more susceptible because of shorter urethra, making it easier for bacteria to reach the bladder.
• Prostate hypertrophy in males:
  • Causes urinary retention. Residual urine creates a warm, moist environment conducive to bacterial growth.

Predisposing Factors:

• Age:  Decreased bladder mucus and IgA production with aging reduces the protective layer against bacteria.
• Incontinence:  Increases the potential for bacterial entry and colonization.
• Retention:  Urine stasis provides a breeding ground for bacteria.
• Diabetes mellitus:  Glucosuria (glucose in urine) provides nutrition for bacteria, increasing risk.  Vascular impairments can also increase risk of infection.
• Structural abnormalities such as: improper valve function at ureter-bladder junction
  • Allows urine, and bacteria, to flow back into the ureters and kidneys, causing pyelonephritis (vesicoureteral reflux).
• Recurrent or prolonged catheterization:  Introduces bacteria directly into the urinary tract.
• Bloodstream infection:  Bacteria can seed kidneys via hematogenous spread.

Symptoms & Signs:

• Bladder/urethral infection:  Burning sensation during urination (dysuria), increased frequency (often caused by hyperactive bladder from irritation), urgency, nocturia (waking up at night to urinate).
• Kidney infection:  Fever, flank pain, malaise, nausea, and vomiting.
• Signs of infection:  Redness, warmth, swelling in affected areas.  Edema in the zone of infection. Fever, feeling tired or generally unwell, nausea.

Lab Tests:

• Urinalysis findings:
  • White blood cells (WBCs): Indicates immune response.
  • Bacteriuria: Sign of infection.
  • Pus/Cloudy urine: Related to infection and inflammatory exudate.
  • Hematuria: Blood in urine, indicating glomerular or urinary tract damage.

Pathology and Damage:

• Infection causes inflammation, increased WBC proliferation and changes in WBC counts (e.g., neutrophilia, leukocytosis ), tissue necrosis, formation of abscesses.
• Chronic infections can lead to scarring and loss of kidney function.

Risk Factors:

• Incomplete bladder emptying due to weak detrusor muscle or flaccid neurogenic bladder or prostatic hypertrophy or urethral strictures/obstructions.
• Menopause due to decreased levels of mucus and protective normal flora (e.g., lactobacillus)
• Impaired blood supply:
  • Weak immune response to infection.
  • Lower white blood cell proliferation.
  • Often immunosuppressed due to comorbidities like HIV.
• Other risk factors:
  • Immobility: Bedridden patients.
  • Use of catheters: Most common Iatrogenic cause of UTIs in Canada.
  • Diabetes: Promotes bacterial growth via glucosuria.

Treatment & Prevention:

• Antibiotics:  Target bacteria and clear the infection.
• Good hygiene:  Proper wiping, hydration, and avoiding irritants.
• Treat structural abnormalities:  Surgical correction if needed.
• Cranberry & Blueberry Juice:  Tannins are thought to reduce capability of E. coli adhering to bladder mucosa
• Address underlying conditions that are risk factors:

Control diabetes, avoid catheters when possible, and manage prostatic hypertrophy to prevent recurrent infections.

Summary:

UTIs, most commonly caused by E. coli, often ascend from the urethra to the bladder and potentially the kidneys, especially with risk factors such as short urethra, retention, or structural issues. UTIs present with symptoms of dysuria, urgency, frequency, and systemic signs like fever and malaise. In elderly or immunocompromised individuals, response may be blunted, and risk factors like retention, immobility, and catheter use increase the likelihood of infection. Good hygiene, prompt treatment, and managing predisposing factors are essential for prevention of complications and recurrent UTIs as well as ensuring long-term health.