Etiology

Pathogens

• Escherichia coli: leading cause of UTI (approx. 80%)
  • Ten times more common in females (shorter urethras colonized by fecal microbiota).
• Staphylococcus saprophyticus: 2nd leading cause of UTI in sexually active women
• Klebsiella pneumoniae: 3rd leading cause of UTI
• Proteus mirabilis
  • Produces ammonia, giving the urine a pungent or irritating smell
  • Associated with struvite stone formation
• Nosocomial bacteria: Serratia marcescens, Enterococci spp., and Pseudomonas aeruginosa are associated with increased drug resistance.

Tip

• Urethritis is often caused by sexually transmitted infections (STIs), e.g. N gonorrhoeae.
• UTIs are generally caused by bacteria from the gastrointestinal tract, e.g. E coli.

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Pathophysiology

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Clinical features

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Diagnostics

Urinalysis

• Pyuria: presence of white blood cells (WBCs) in the urine
  • Positive leukocyte esterase: an enzyme produced by WBC
  • ≥ 5 WBC/HPF
• Bacteriuria: presence of bacteria in the urine
  • Positive urinary nitrites: indicate bacteria that convert nitrates to nitrites (most commonly gram-negative bacteria; e.g., E.coli, Klebsiella, Proteus mirabilis)
• Other findings
  • Leukocyte casts may indicate pyelonephritis.
  • Micro- or macroscopic hematuria may be present.
  • Alkaline urine (pH > 8) and struvite crystals in sediment: indicate urease-producing organisms (e.g., Proteus, Klebsiella, Staphylococcus saprophyticus)

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Treatment

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UTI in pregnancy

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• Pregnancy may increase the risk of recurrent bacteriuria and UTIs.
• Treatment
  • Empiric antibiotics for ASB and lower UTI considered appropriate during pregnancy include:
    • Fosfomycin
    • Beta-lactam antibiotics for 5–7 days
      • Oral cephalosporins (e.g., cefpodoxime)
      • Aminopenicillins plus beta-lactamase inhibitors (e.g., amoxicillin/clavulanic acid)

Catheter-associated UTI (CAUTI)

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• Definitions
  • Catheter-associated UTI (CAUTI): symptomatic UTI occurring in a patient with an indwelling urinary catheter OR within 48 hours after removal of a urinary catheter
  • Catheter-associated asymptomatic bacteriuria (CAASB): bacteriuria (≥ 105CFU/mL) without symptoms in a patient with an indwelling urinary catheter OR within 48 hours after removal of a urinary catheter
• Treatment
  • Catheter removal or replacement
    • Remove if no longer necessary.
    • Replace if still necessary and present for > 2 weeks.
  • Antibiotic therapy
    • Guided by culture results and local resistance patterns
    • Duration: typically 7–14 days depending on the resolution of symptoms