Urinary Tract Infections

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UTI Basics - Pee Problem Primer

Urinary Tract Infection (UTI) Diagram

  • 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.

  • Common Uropathogens:
    OrganismKey Associations / Virulence Factors
    Escherichia coli (UPEC)Most common; P fimbriae, haemolysin, K antigen
    Staphylococcus saprophyticusSexually active ♀; "Honeymoon cystitis"
    Klebsiella pneumoniaeMucoid colonies; catheters, nosocomial
    Proteus mirabilisUrease → ↑pH, struvite stones (staghorn)
    Enterococcus faecalisNosocomial, elderly, catheterized, VRE
    Pseudomonas aeruginosaCatheters, HA-UTI, blue-green pigment, resistance
    Candida albicansFungal; 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 UTI: Cystitis vs. Pyelonephritis Symptoms

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

Diagnosis Decoded - Lab Clue Hunt

Urine dipstick results and recommendations for UTIs

  • 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.

Practice Questions: Urinary Tract Infections

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A patient presents with urethral discharge. Gram stain shows intracellular gram-negative diplococci. What is the causative organism?

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Flashcards: Urinary Tract Infections

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Which part of males are resistant to gonococcal infection?_____

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Which part of males are resistant to gonococcal infection?_____

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