Urinary Tract Infections

UTI Basics - Pee Problem Primer

• Definition: Microbial infection anywhere along the urinary tract.
• Epidemiology: Females > males; common in young women, elderly.
• Risk Factors: 📌 Sexual activity, Catheterization, Obstruction, Diabetes, Immunosuppression, Pregnancy.
• Classification:
  • Site: Upper (pyelonephritis) vs Lower (cystitis, urethritis).
  • Complexity: Uncomplicated (healthy female) vs Complicated (e.g., male, catheter, obstruction).
  • Pattern: Recurrent UTI (≥2 in 6 months or ≥3 in 1 year); Relapse vs Reinfection.

⭐ Most common cause of uncomplicated UTI is E. coli.

Bugs & Routes - Microbe Mayhem March

• Common Pathogens & Key Associations:
  • E. coli: ~80%
  • Staphylococcus saprophyticus: Key in young women.

    ⭐ Staphylococcus saprophyticus is a common cause of UTI in sexually active young women, often called 'honeymoon cystitis'.

  • Klebsiella
  • Proteus: Struvite stones, alkaline urine; Urease: $Urea + H₂O \rightarrow 2NH₃ + CO₂$
  • Enterococcus
  • Pseudomonas: Catheter, hospital-acquired
• 📌 KEEPS Mnemonic: Klebsiella, E. coli, Enterococcus/Enterobacter, Proteus/Pseudomonas, S. saprophyticus.
• Routes of Infection:
  • Ascending (most common)
  • Hematogenous, Lymphatic (both rare)
• Virulence Factors:
  • Pili/fimbriae (adhesion)
  • Hemolysin
  • Urease (Proteus)

Signs & Sleuthing - Symptom Spotter's Guide

• Clinical Features:

  Feature	Cystitis	Pyelonephritis
  Symptoms	Dysuria, frequency, urgency, suprapubic pain, hematuria	Fever, chills, flank pain, CVA tenderness, N/V, +/- cystitis sx

• Atypical: Elderly (confusion), Children (fever).
• Urinalysis:
  • Dipstick: Leukocyte esterase (LE), Nitrites.

  ⭐ Presence of nitrites on urine dipstick is highly specific for Enterobacteriaceae infection.

  • Microscopy: Pyuria (>10 WBCs/hpf), Bacteriuria, RBCs, WBC casts (pyelonephritis).
• Urine Culture:
  • Indications: Complicated UTI, pyelonephritis, recurrent UTI, treatment failure, pregnancy.
  • Significant Bacteriuria: ≥10⁵ CFU/mL (midstream); ≥10² CFU/mL (symptomatic women/catheter).

Treatment Tactics - Bug Battle Blueprint

• General Measures: ↑Hydration, regular voiding.
• Uncomplicated Cystitis (Outpatient):
  • Nitrofurantoin 100mg BD x 5 days
  • TMP-SMX DS BD x 3 days
  • Fosfomycin 3g single dose
  • Avoid fluoroquinolones if alternatives exist.
• Complicated UTI / Pyelonephritis:
  • Longer course, broader spectrum (e.g., Fluoroquinolones, 3rd gen Cephalosporins, Aminoglycosides).
  • IV for severe cases. Tailor to culture results.
• Pain Relief: Phenazopyridine.

⭐ Nitrofurantoin is a first-line agent for uncomplicated cystitis but should be avoided if GFR < 30-60 mL/min or in suspected pyelonephritis.

Special Cases - Tricky Tract Troubles

• UTI in Pregnancy: Screen & treat ASB. Risks: pyelo, preterm. Safe: Cephalexin, Nitrofurantoin (not term), Amoxicillin. Avoid: FQ, Tetracyclines, TMP-SMX (1st/3rd).

  ⭐ ASB in pregnancy: screen & treat to prevent pyelonephritis, preterm birth.

• CAUTI: Nosocomial. Dx: symptoms + ≥10³ CFU/mL (catheter). Mgmt: change catheter, treat symptomatic.
• ASB: ≥10⁵ CFU/mL, no symptoms. Treat if:
  • Pregnant
  • Pre-urologic procedure (mucosal bleed)

• Prostatitis: Linked to recurrent UTI in men.

Prevention & Pitfalls - Defense & Dangers

• Recurrent UTI Prevention:
  • Behavioral: Post-coital voiding, adequate hydration.
  • Antimicrobial prophylaxis: Continuous low-dose, post-coital.
  • Non-antimicrobial: Cranberry (limited evidence), topical estrogen (postmenopausal), D-mannose.
• Complications (Dangers):
  • Pyelonephritis, renal/perinephric abscess.
  • Papillary necrosis, sepsis/urosepsis.
  • Chronic pyelonephritis, renal scarring.
  • Xanthogranulomatous pyelonephritis.

⭐ Emphysematous pyelonephritis: a life-threatening necrotizing infection with gas in renal tissues, predominantly affecting diabetic patients.

High‑Yield Points - ⚡ Biggest Takeaways

• E. coli is the leading uropathogen in most UTIs.
• Significant bacteriuria is >10^5 CFU/mL; pyuria is crucial for diagnosis.
• Nitrofurantoin, TMP-SMX, and Fosfomycin are first-line for uncomplicated cystitis.
• Complicated UTIs (e.g., males, pregnancy, catheters) need broader/longer antibiotic courses.
• Treat asymptomatic bacteriuria mainly in pregnancy and pre-urologic procedures.
• Sterile pyuria may indicate urogenital TB or Chlamydia.
• CAUTI is the most common hospital-acquired infection; prioritize prevention.