Harvey's Garden

Urinary tract infections

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aliasesUTI, UTIs, Catheter-associated UTI, Urinary tract infection

4 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) tNo (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
  • Cystitis (Lower UTI):
    • Dysuria, frequency, urgency, suprapubic tenderness.
    • Hematuria (hemorrhagic cystitis). c
    • Absence of systemic symptoms (fever, chills). c
  • Pyelonephritis (Upper UTI):
    • Fever, chills, flank pain, CVA tenderness, N/V.
    • Systemic signs of sepsis (tachycardia, hypotension).

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)

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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

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Treatment

  • Classification:
    • Uncomplicated: Non-pregnant, premenopausal, immunocompetent females with normal genitourinary (GU) anatomy.
    • Complicated: Males, pregnant women, postmenopausal women, immunocompromised (DM, CKD, HIV), structural/functional GU abnormalities (neurogenic bladder, stone, BPH), indwelling catheters, or hospital-acquired.
  • Uncomplicated Cystitis:
    • First-line: Nitrofurantoin (5 days), TMP-SMX (3 days, if local resistance <20%), or Fosfomycin (single dose). c
      • Nitrofurantoin: Concentrates rapidly and exclusively in the urine/bladder. Minimal systemic absorption reduces systemic side effects and limits collateral damage to bowel flora.
  • 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

  • Pathophysiology & Risk:
    • Progesterone-induced ureteral relaxation -> hydronephrosis/stasis (R > L).
    • Pathogens: E. coli (#1), Klebsiella, Proteus, GBS.
  • Screening:
    • Routine Urine Culture (UCx) for ALL pregnant pts at 12–16 weeks (or 1st visit).
  • Asymptomatic Bacteriuria (ASB) & Acute Cystitis:
    • Must treat ASB to prevent pyelonephritis, preterm labor, and low birth weight.
    • Safe Abx: Nitrofurantoin (avoid 1st trimester & ≥37 wks), Cephalexin, Amoxicillin-clavulanate, Fosfomycin.
    • Contraindicated Abx: TMP-SMX (1st trimester -> NTDs; 3rd trimester -> kernicterus), Fluoroquinolones (cartilage damage).
    • GBS Bacteriuria: Treat UTI now + mandatory IV Penicillin during labor (skip 36–37 wk screen).
    • Follow-up: Mandatory test-of-cure UCx 1–2 weeks post-treatment.
  • Acute Pyelonephritis:
    • Presentation: Fever, chills, flank pain, costovertebral angle (CVA) tenderness, N/V.
      • Obstetric Findings: Uterine contractions, signs of preterm labor.
    • Management: Inpatient admission + IV Ceftriaxone or Ampicillin/Gentamicin. c
    • Transition to PO Abx once 24–48 hrs afebrile (10–14 days total course).
    • Requires daily low-dose suppressive Abx (e.g., Nitrofurantoin) for the remainder of pregnancy.
  • Key Complications:
    • Maternal: ARDS, septic shock, perinephric abscess.
    • Fetal/Obstetric: Preterm delivery, low birth weight, perinatal mortality.

Catheter-associated UTI (CAUTI)

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