Urinary Tract Infections

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UTI Basics - When Pee Burns

Urinary Tract Infection (UTI): Microbial invasion & inflammation of the urinary system.

  • Classification:
    TypeDescription
    UncomplicatedHealthy, non-pregnant adult female
    ComplicatedStructural/functional abnormality; comorbidity
    Lower UTICystitis (bladder), Urethritis (urethra)
    Upper UTIPyelonephritis (kidney)
    Recurrent≥2 episodes/6 months or ≥3 episodes/1 year
  • Risk Factors: Female sex, sexual activity, catheterization, obstruction (e.g., stones, BPH), diabetes, immunosuppression.
  • Common Pathogens: Escherichia coli (most common, ~80%), Staphylococcus saprophyticus, Klebsiella spp., Proteus mirabilis.

Female and Male Urinary Tracts

⭐ Uncomplicated UTI is most common in young, sexually active women; E. coli accounts for ~80% of cases.

Bugs & Biofilms - Culprit Critters Crawl

  • Routes: Ascending (main), haematogenous. Biofilms on catheters/urothelium aid persistence, ↑drug resistance.
  • Virulence: Adhesins (P-fimbriae), toxins (haemolysin), enzymes (urease), capsules.

UTI pathogenesis and colonization pathways

Common Pathogens: 📌 Mnemonic: "Every Patient Should Know" (E. coli, Proteus, S. saprophyticus, Klebsiella)

PathogenKey Features / Notes
Escherichia coliUPEC; P-fimbriae (pyelo risk), haemolysin. Most common (~80%).
Staphylococcus saprophyticusYoung, sexually active women; Adhesins. "Honeymoon cystitis".
Klebsiella pneumoniaeCapsule; Nosocomial, diabetics. Mucoid.
Proteus mirabilisUrease → $NH_3$ → ↑alkaline urine; Swarming motility; Struvite stones.

Signs & Samples - Symptom Sleuthing & Tests

Symptom Spectrum: Cystitis vs. Pyelonephritis

FeatureCystitis (Lower UTI)Pyelonephritis (Upper UTI)
Local SymptomsDysuria, frequency, urgency, suprapubic pain, hematuria. No systemic upset.Often preceded/accompanied by cystitis symptoms.
SystemicAbsentFever (>38°C), chills, rigors, flank pain, CVA tenderness, nausea/vomiting.
  • Sample: Mid-Stream Urine (MSU) preferred to ↓contamination.
  • Dipstick:
    • Leukocyte esterase: +ve (pyuria)
    • Nitrites: +ve (Enterobacteriaceae like E.coli) 📌 Nitrites = Gram-Negative Organisms
    • Blood: +/- (hematuria)
    • Protein: Mild, if present.
  • Microscopy:
    • Pyuria: WBCs >5-10/hpf.
    • Bacteriuria: Significant if >10^5 CFU/mL (MSU in women); ≥10^3 CFU/mL (MSU in men/catheter); any growth in suprapubic aspirate.
    • WBC Casts: Highly suggestive of pyelonephritis/renal involvement.

⭐ Presence of WBC casts in urine is pathognomonic for pyelonephritis or renal parenchymal inflammation.

Urine sediment microscopy: cells, casts, and crystals

Diagnostic Algorithm for Suspected UTI:

Treatment & Tricks - Bug Battle Blueprint

Antibiotic Choices:

ConditionFirst-lineAlternativesDuration
Uncomplicated CystitisNitrofurantoin 100mg BD; TMP-SMX DS BD; Fosfomycin 3g x1Fluoroquinolones (if unsuitable)3-5 days
Pyelonephritis (OPD)Fluoroquinolones (Cipro 500mg BD / Levo 750mg OD)TMP-SMX (C/S known); Ceftriaxone 1g IV x1 then oral7-14 days
Pyelonephritis (IPD)IV Ceftriaxone; IV Pip-TazIV Fluoroquinolones; Carbapenems (ESBL)10-14 days
UTI in PregnancyCephalexin 500mg QID; Amoxi-Clav; Nitrofurantoin (not 1st/term)Fosfomycin7 days
-   Behavioral mod (hydration, voiding), post-coital voiding.
-   Prophylaxis: Continuous low-dose (Nitrofurantoin **50-100mg OD**, TMP-SMX **SS OD**) or post-coital.
  • CAUTI (Catheter-Associated UTI):
    • Treat only if symptomatic.
    • Promptly remove/replace catheter.
    • Abx per C/S 7-14 days (catheter out: 7d may suffice).
  • Asymptomatic Bacteriuria (ASB):
    • Screen & treat: Pregnant women; pre-urologic procedures (mucosal trauma).

    ⭐ Asymptomatic bacteriuria in pregnant women requires treatment to prevent complications like pyelonephritis and preterm labor.

High‑Yield Points - ⚡ Biggest Takeaways

  • E. coli is the most common uropathogen.
  • Uncomplicated cystitis: Common in healthy, non-pregnant women.
  • Complicated UTIs: Associated with pregnancy, diabetes, male sex, or structural issues.
  • Diagnosis: Urine culture (>10^5 CFU/mL) and pyuria (>5 WBCs/hpf).
  • Asymptomatic bacteriuria: Treat in pregnancy and pre-urological procedures.
  • Acute pyelonephritis: Fever, flank pain, CVA tenderness; may need IV antibiotics.
  • Recurrent UTIs: ≥2 episodes/6 months or ≥3 episodes/1 year.

Practice Questions: Urinary Tract Infections

Test your understanding with these related questions

A boy is suffering from acute pyelonephritis. The most specific investigation to confirm the diagnosis is:

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Flashcards: Urinary Tract Infections

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Acute pyelonephritis may present with _____ in the urine +/- WBC casts

TAP TO REVEAL ANSWER

Acute pyelonephritis may present with _____ in the urine +/- WBC casts

WBCs

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