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Infectious disease

Urinary tract infections

Cystitis vs pyelo vs CAUTI vs asymptomatic bacteriuria. Symptoms define infection, not the UA alone.

Nick Peterson5 min6 questions1 trials

Name it before you treat it

Symptoms define a UTI. Pyuria, a cloudy bag, and a positive culture without a syndrome are not a license to prescribe ( ASB, ). Complicated UTI is infection beyond the bladder — pyelonephritis, CAUTI, fever, or bacteremia — in any sex (CID 2025;ciaf460).

Four labels

  • ASB

    Asymptomatic bacteriuria

    ≥10⁵ CFU/mL and no UTI symptoms, pyuria or not. Do not treat except pregnancy, before mucosal urologic procedures, and (controversially) the first 1–2 months after renal transplant.

  • Cystitis

    Uncomplicated lower tract

    Frequency, urgency, dysuria, suprapubic pain in an otherwise healthy nonpregnant woman. Men with UTI symptoms: think prostatitis.

  • Complicated

    Beyond the bladder

    Fever, rigors, CVA tenderness, obstruction, stones, catheters, men, immunocompromise, pregnancy pyelo, transplants.

  • CAUTI

    Catheter-associated

    Symptoms with no other source plus ≥10³ CFU/mL from a catheter in place >2 days, or voided urine within 48 h of removal ().

Cystitis vs pyelo / CAUTI

Uncomplicated cystitis

  • Clinical. Dysuria + frequency without vaginal discharge is >90% likely a UTI. UA confirms; absence of pyuria argues hard against cystitis. Outpatient UA is optional unless immunocompromised or complicated-risk.
  • Nitrite is positive with Enterobacterales. Get a culture if male, atypical, failing at 48–72 h, or recurring within 3 months.
  • E. coli, Klebsiella, Proteus, S. saprophyticus. True enterococcal cystitis is uncommon.
  • Ddx: vaginitis, urethritis, PID, stone, structural disease.

Complicated / pyelo / CAUTI

  • ~30% of febrile UTIs are bacteremic — older, flank/suprapubic pain, high CRP, hypotension ().
  • Culture everyone. Image if ill, obstruction suspected, or symptoms persist.
  • Same organisms plus Serratia, Morganella, Providencia, Pseudomonas, Citrobacter. S. aureus in urine is bacteremia until proven otherwise.
  • CAUTI: replace/remove the catheter and reculture from the new one before antibiotics. Biofilm lies.
SyndromeRegimenAvoid
Uncomplicated cystitisNitrofurantoin 100 mg BID × 5 d, or TMP-SMX DS BID × 3 d if local resistance <20%, or fosfomycin 3 g × 1. Alt: oral β-lactam (1st-gen > 3rd-gen) × 7 d, or a single-dose aminoglycoside if MDRO.Empiric FQ. Nitrofurantoin if CrCl <40. Empiric TMP-SMX if E. coli resistance >20% (often ~30%). TMP-SMX and nitrofurantoin in the 1st trimester and at term.
Complicated / pyelo, outpatientCipro 500 mg BID or levo 750 mg × 5–7 d, or TMP-SMX DS BID × 7–10 d if susceptible. Alt: amox-clav or an oral cephalosporin. A one-time IV CTX before oral therapy is fine.Nitrofurantoin and fosfomycin — they do not treat parenchyma or prostate.
Complicated / pyelo, inpatientCTX or cefepime. Carbapenem if prior ESBL. Narrow to oral when improving. Duration follows the oral agent: FQ 5–7 d, TMP-SMX 7–10 d, β-lactam 10–14 d.Leaving a coated stent or Foley in as “the culture source.”
CAUTIExchange the catheter. Add vancomycin if recent instrumentation or MRSA in urine, then narrow. 7 days if improving; 10–14 if slow.Screening asymptomatic catheterized patients.
ProstatitisA FQ (better penetration) or TMP-SMX. Up to 6 weeks.Nitrofurantoin / fosfomycin as the plan.

Candiduria and recurrence

  • Asymptomatic candiduria is colonization. Treat only if symptomatic, neutropenic, or before a urologic procedure (, ).
  • Fluconazole 200–400 mg PO daily × 14 days if susceptible. Fluconazole-resistant C. glabrata or C. krusei: amphotericin × 1–7 days.

Recurrent simple cystitis

  • Behavior: 2–3 L water/day, post-coital voiding, no spermicide, wipe front to back.
  • Vaginal estrogen after menopause, methenamine, and cranberry have signals (; Cochrane 2023). D-mannose and probiotics have not ().
  • Antibiotic prophylaxis (TMP-SMX or nitrofurantoin), post-coital or continuous, if ≥2 UTI / 6 months and behavior change failed.
  • Recurrent complicated UTI with resistant organisms: review old micro, involve ID ± urology. Prophylaxis here breeds more resistance — do not do it.