Urinary tract infections

UTI Basics - Pee Under Pressure

• Etiology: Primarily E. coli (>80%), followed by Klebsiella, Proteus, Enterococcus, S. saprophyticus (sexually active young women).
• Pathophysiology: Ascending infection from urethra → bladder (cystitis) → kidneys (pyelonephritis). Hematogenous spread is rare.
• Risk Factors: Female sex (short urethra), sexual activity, catheterization (biofilms!), urinary stasis (BPH, stones), diabetes, pregnancy.
• Classification:
  • Uncomplicated: Healthy, non-pregnant, premenopausal female.
  • Complicated: All others (male, pregnant, obstruction, catheter, immunosuppressed).

⭐ Sterile pyuria (WBCs in urine without bacteria) suggests urethritis from Chlamydia or Neisseria, or TB cystitis.

Diagnosis - The Urine Detective

• Urinalysis (UA): Initial screen.
  • Leukocyte Esterase: Suggests pyuria (WBCs).
  • Nitrites: Specific for gram-negative bacteria (e.g., E. coli).
• Urine Culture: Gold standard for diagnosis & sensitivities.
  • Significant bacteriuria: $> extbf{10^5}$ CFU/mL.
• Imaging (CT/Ultrasound): Reserved for complicated UTI, suspected obstruction, or pyelonephritis.

⭐ Sterile Pyuria: Presence of WBCs in urine with a negative standard culture. Think Chlamydia trachomatis, Ureaplasma urealyticum, or renal tuberculosis.

Uncomplicated UTI - Simple & Swift

• Definition: Acute cystitis in healthy, non-pregnant, premenopausal females. Excludes structural/functional urinary tract abnormalities.
• Etiology: Predominantly E. coli (>80%). Others: Staphylococcus saprophyticus (especially in sexually active young women), Klebsiella, Proteus.
• Clinical: Dysuria, frequency, urgency, suprapubic pain. Absence of systemic symptoms (fever, chills, flank pain) is key.
• Diagnosis:
  • Urine dipstick: Positive for leukocyte esterase & nitrites.
  • Urinalysis: Pyuria (WBCs), bacteriuria.
  • Urine culture is definitive but often deferred.
• Treatment (Short-course):
  • Nitrofurantoin: 100 mg BID for 5 days.
  • TMP-SMX: 1 DS tab BID for 3 days (if local E. coli resistance <20%).
  • Fosfomycin: 3 g single dose.

⭐ High-Yield: Positive nitrites on dipstick are highly specific for gram-negative bacteria (Enterobacteriaceae family, like E. coli), which can convert urinary nitrates to nitrites.

Complicated UTI - Kidney on Fire

UTI in the presence of factors that ↑ risk of failing therapy (e.g., male sex, obstruction, catheter, diabetes, pregnancy). Includes pyelonephritis & perinephric abscess.

• Pyelonephritis: Infection of kidney parenchyma.
  • Triad: Fever, CVA tenderness, nausea/vomiting.
  • Urinalysis: WBC casts are pathognomonic.
• Perinephric Abscess: Pus collection around the kidney.
  • Suspect if no improvement after 48-72h of IV antibiotics.
  • Diagnosis: CT or ultrasound.

⭐ WBC casts are fragile and disintegrate quickly; their presence in a fresh urine sample strongly suggests pyelonephritis.

High‑Yield Points - ⚡ Biggest Takeaways

• E. coli is the most common uropathogen, causing >80% of UTIs.
• Distinguish uncomplicated cystitis (healthy, non-pregnant women) from complicated UTIs (males, pregnancy, catheters).
• Urinalysis showing leukocyte esterase and nitrites is key; urine culture is the gold standard.
• Only treat asymptomatic bacteriuria in pregnant patients or prior to urologic procedures.
• Pyelonephritis (fever, flank pain) requires broader antibiotics (e.g., fluoroquinolones) than simple cystitis.
• CAUTI is the top nosocomial infection; remove the catheter promptly.