Urinary Tract Infections

UTI Basics - Pee Problem Primer

• Definition: Microbial infection anywhere in the urinary tract (kidneys, ureters, bladder, urethra).
• Sites & Types:
  • Lower UTI: Cystitis (bladder), urethritis (urethra).
  • Upper UTI: Pyelonephritis (kidneys).
• Categories:
  • Uncomplicated: Healthy, non-pregnant women with normal urinary tract.
  • Complicated: Factors increasing risk (e.g., male, catheter, obstruction, diabetes, pregnancy).

⭐ Definition of recurrent UTI: ≥2 infections in 6 months or ≥3 in 1 year.

Culprits & Causes - Rogue's Gallery

• Common Uropathogens:

  Organism	Key Associations / Virulence Factors
  Escherichia coli (UPEC)	Most common; P fimbriae, haemolysin, K antigen
  Staphylococcus saprophyticus	Sexually active ♀; "Honeymoon cystitis"
  Klebsiella pneumoniae	Mucoid colonies; catheters, nosocomial
  Proteus mirabilis	Urease → ↑pH, struvite stones (staghorn)
  Enterococcus faecalis	Nosocomial, elderly, catheterized, VRE
  Pseudomonas aeruginosa	Catheters, HA-UTI, blue-green pigment, resistance
  Candida albicans	Fungal; DM, catheters, prolonged antibiotics

• Routes of Infection:
  • Ascending (dominant): Urethra → bladder (cystitis) → kidneys (pyelonephritis).
  • Haematogenous (rare): e.g., S. aureus, Candida spp. from distant foci.

⭐ E. coli is the most common uropathogen, accounting for ~80% of uncomplicated UTIs.

Signs & Symptoms - Bladder Blues

• Cystitis (Lower UTI):
  • Dysuria, frequency, urgency
  • Suprapubic pain/tenderness
  • +/- Hematuria
  • Usually afebrile, no systemic upset
• Pyelonephritis (Upper UTI):
  • Systemic: Fever (>38°C), chills
  • Loin/flank pain, CVA tenderness
  • Nausea, vomiting
  • Cystitis symptoms may co-exist
• Special Populations:
  • Elderly: Confusion, falls, incontinence (often afebrile)
  • Children: Fever, irritability, poor feeding
  • CAUTI: Fever, altered mental status, lethargy

⭐ Flank pain, fever, and CVA tenderness are classic signs of pyelonephritis.

Diagnosis Decoded - Lab Clue Hunt

• Urine Dipstick:
  • Leukocyte Esterase (LE): Detects pyuria (WBCs).
  • Nitrites: Detects Enterobacteriaceae (e.g., E. coli).
• Urine Microscopy:
  • WBCs: >5-10/hpf = pyuria.
  • Bacteria: Presence noted.
  • WBC casts: Suggest pyelonephritis.
• Urine Culture & Sensitivity (C/S): Gold standard.
  • Mid-stream urine (MSU).
  • Identifies organism & antibiotic susceptibility.

⭐ Significant bacteriuria: ≥10⁵ CFU/mL (cystitis, women). Lower for symptomatic men/catheter (≥10³ CFU/mL).

Treatment Tactics - Bug Battle Plan

⭐ Nitrofurantoin is a first-line agent for uncomplicated cystitis but should be avoided if GFR < 30 mL/min or in suspected pyelonephritis.

• Key Principles:
  • Empiric therapy; tailor to culture/sensitivity.
  • Consider local resistance.
  • Adequate hydration.

High‑Yield Points - ⚡ Biggest Takeaways

• E. coli (Uropathogenic E. coli - UPEC) is the most common cause of UTIs.
• Significant bacteriuria is defined as >10^5 Colony Forming Units (CFU)/mL in a mid-stream urine sample.
• Uncomplicated UTIs typically occur in healthy, non-pregnant women; complicated UTIs involve risk factors like male sex, pregnancy, or catheters.
• Acute pyelonephritis presents with fever, flank pain, and costovertebral angle (CVA) tenderness; WBC casts in urine are characteristic.
• Treat asymptomatic bacteriuria primarily in pregnant women and patients undergoing invasive urologic procedures.
• Recurrent UTIs are defined as ≥2 infections in 6 months or ≥3 infections in 1 year.