Harvey's Garden

Urinary tract infections

3 min read

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.

Classification

FeatureUpper UTI (Pyelonephritis)Lower UTI (Cystitis)
LocationKidney / Renal PelvisBladder / Urethra
Systemic SxYes (Fever, Chills, Malaise)No (Typically Afebrile)
Key SignCVA Tenderness, Flank PainSuprapubic Tenderness
Urinary SxMay be presentPredominant (Dysuria, Frequency)
UA KEY FINDINGWBC CastsNO WBC Casts
SeverityMore SevereLess Severe
ManagementOften Inpatient, IV AntibioticsUsually Outpatient, Oral Antibiotics

Clinical features

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)

Drawing 2025-03-29 16.01.03.excalidraw

⚠ Switch to EXCALIDRAW VIEW in the MORE OPTIONS menu of this document. ⚠ You can decompress Drawing data with the command palette: ‘Decompress current Excalidraw file’. For more info check in plugin settings under ‘Saving’

Excalidraw Data

Text Elements

Lactose Fermenters

Nitrate Reducers

Proteus

Urease Production

Helicobacter pylori Ureaplasma urealyticum Staphylococcus saprophyticus (3rd) Corynebacterium spp.

E. coli (1st) Enterobacter Citrobacter

Klebsiella (2nd)

Pseudomonas

Embedded Files

1d31e51a4dbefce0670aa7da4357fddf403fccdd: Gemini_Generated_Image_wapvdcwapvdcwapv.png

32b3a48d96d30b68f178804fbc510ef15c83cea3: Gemini_Generated_Image_ednoi4ednoi4edno.png

12d8036895fa186aba0d7b9b88f6b88c31682b83: Gemini_Generated_Image_o62ynao62ynao62y.png

Link to original

Treatment

  • Uncomplicated Cystitis:
    • First-line: Nitrofurantoin (5 days), TMP-SMX (3 days, if local resistance <20%), or Fosfomycin (single dose).
  • Complicated Cystitis:
    • Longer course (7-14 days) of oral fluoroquinolones (e.g., Ciprofloxacin) or TMP-SMX.
  • Outpatient Pyelonephritis (Mild-to-Moderate):
    • Oral fluoroquinolones (e.g., Ciprofloxacin, Levofloxacin) for 7-14 days.
  • Inpatient Pyelonephritis (Severe):
    • IV antibiotics (e.g., Fluoroquinolones, extended-spectrum Cephalosporins like Ceftriaxone, or Piperacillin-tazobactam).
  • Asymptomatic Bacteriuria:
    • Generally not treated, except in pregnant patients or before urologic procedures.

Mnemonic

  • 口诀——三光政策（急性膀胱炎治疗三天）首选喹诺酮类药物（妊娠的以及＜18岁的首选三代头孢）
  • 口诀——两个周瑜（急性肾盂肾炎治疗两周）喹诺酮类药物

UTI in pregnancy

  • 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)

  • 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
  • Risk factors
    • Duration of catheter use, especially >48 hr (most important)
    • Female sex
    • Advanced age
    • Diabetes mellitus
  • 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

Graph View

Backlinks