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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Complicated UTI includes pyelonephritis, sepsis, obstruction, catheter, urinary tract abnormality, renal transplant, pregnancy, male UTI, or major comorbidity
- CAUTI requires compatible symptoms plus significant bacteriuria; pyuria alone does not diagnose infection in catheterized patients
- Obtain urine culture before antibiotics in complicated UTI, pyelonephritis, recurrent infection, treatment failure, or CAUTI
- Replace or remove an indwelling catheter if it has been in place more than about 2 weeks and is still needed
- Empiric therapy depends on severity and resistance risk: ceftriaxone, cefepime, piperacillin-tazobactam, carbapenem, or fluoroquinolone when appropriate
- Do not treat asymptomatic bacteriuria except pregnancy or before invasive urologic procedures with mucosal bleeding
Overview
Urinary tract infections range from uncomplicated cystitis to pyelonephritis, bacteremia, and septic shock. Complicated UTI is not simply "more severe cystitis"; it refers to infection in a host or urinary tract context that increases risk of treatment failure or adverse outcomes. Catheter-associated UTI is a healthcare-associated infection driven by biofilm and ascending bacterial colonization. Step 2 CK commonly tests the distinction between symptomatic infection and asymptomatic bacteriuria, especially in elderly or catheterized patients.
Epidemiology
UTIs are among the most common bacterial infections and are a major driver of outpatient antibiotic use and hospital admissions. Escherichia coli is most common overall, but complicated and catheter-associated infections have higher rates of Klebsiella, Proteus, Enterococcus, Pseudomonas, Staphylococcus aureus, Candida colonization, and multidrug-resistant organisms. Risk rises with diabetes, urinary obstruction, stones, neurogenic bladder, instrumentation, and indwelling catheters.
Clinical Features
Symptoms
Cystitis symptoms: dysuria, urinary frequency, urgency, suprapubic discomfort
Pyelonephritis: fever, chills, flank pain, nausea/vomiting, malaise
CAUTI: fever, rigors, flank pain, pelvic discomfort, acute hematuria, or delirium with no alternative source
Urosepsis: hypotension, tachypnea, altered mental status, oliguria
Prostatitis in men: fever, pelvic/perineal pain, obstructive urinary symptoms
Asymptomatic bacteriuria has no localizing urinary symptoms and should usually not be treated
Signs
Suprapubic tenderness in cystitis
Costovertebral angle tenderness in pyelonephritis
Fever, tachycardia, hypotension, or toxic appearance suggests upper tract disease or sepsis
Distended bladder or enlarged tender prostate may suggest obstruction/prostatitis
Catheter obstruction, leakage, purulence, or trauma may be present but is not required
Investigations
First-line
Urinalysis with microscopyPyuria, leukocyte esterase, nitrites, hematuria; nitrite negative does not exclude Enterococcus, Staph saprophyticus, or low bladder dwell time
Urine culture with susceptibilitiesRequired in complicated UTI, pyelonephritis, CAUTI, pregnancy, recurrent infection, men, and treatment failure
Blood culturesIf febrile pyelonephritis, sepsis, immunocompromise, or hospital-acquired infection
Second-line
Renal ultrasound or CT abdomen/pelvisIf obstruction, stone, abscess, emphysematous pyelonephritis, persistent fever >48-72 h, renal transplant, or recurrent complicated infection
Pregnancy testIn reproductive-age patients because pregnancy changes antibiotic choice and treatment threshold
Post-void residualIf retention, neurogenic bladder, recurrent UTI, or suspected obstruction
Specialist
Urology consultationObstructing infected stone, abscess, emphysematous pyelonephritis, urinary retention, or anatomic abnormality
Infectious diseases consultationESBL, CRE, recurrent resistant infection, bacteremia, or complex antibiotic allergies
1
Initial management
- Assess for sepsis and obstruction; infected obstruction requires urgent decompression
- Obtain urine culture before antibiotics when feasible
- Start empiric antibiotics based on severity, local resistance, prior cultures, and risk of ESBL/Pseudomonas
- Hydration, analgesia, and antiemetics; admit if vomiting, pregnancy with pyelonephritis, sepsis, obstruction, or unreliable follow-up
2
Empiric antibiotic options
- Stable pyelonephritis: ceftriaxone IV initial dose then oral step-down if susceptible; oral fluoroquinolone only if local resistance acceptable and patient risk permits
- Severe or healthcare-associated infection: cefepime or piperacillin-tazobactam if Pseudomonas risk; carbapenem if ESBL risk or severe sepsis with prior ESBL
- Enterococcus risk: ampicillin if susceptible; vancomycin if severe beta-lactam allergy or resistant gram-positive concern
- Nitrofurantoin and fosfomycin are for lower tract cystitis only, not pyelonephritis or bacteremia
3
Catheter-associated UTI
- Remove catheter if no longer needed
- If catheter has been in place >2 weeks and still needed, replace it before culture/therapy to reduce biofilm burden
- Do not screen or treat catheter-associated asymptomatic bacteriuria except pregnancy or selected urologic procedures
- Use shortest effective duration; commonly 7 days if prompt response, longer if delayed response or bacteremia
4
Prevention
- Avoid unnecessary catheters; use aseptic insertion and closed drainage
- Remove catheters early; consider external catheter or intermittent catheterization when appropriate
- Do not use chronic prophylactic antibiotics for indwelling catheters
Complications
- Pyelonephritis: Upper tract infection with risk of bacteremia
- Urosepsis: Common source of septic shock in older adults
- Renal or perinephric abscess: Persistent fever despite therapy
- Emphysematous pyelonephritis: Gas-forming infection, classically in diabetes
- Obstructive pyelonephritis: Infected stone or obstruction requiring urgent drainage
USMLE Step 2 CK Exam Tips
- 1Elderly patient with bacteriuria but no urinary symptoms or systemic signs = do not treat, even if urine culture is positive
- 2Pregnancy + asymptomatic bacteriuria = treat because it prevents pyelonephritis and adverse pregnancy outcomes
- 3Nitrofurantoin does not reach renal parenchyma; never choose it for pyelonephritis
- 4Fever persists after 72 hours of pyelonephritis therapy = image for abscess, stone, or obstruction
- 5Infected obstructing stone = antibiotics plus urgent decompression, not outpatient oral antibiotics
- 6CAUTI management includes removing or replacing the catheter, not just antibiotics
- 7S aureus in urine without instrumentation can signal hematogenous spread or endocarditis; think beyond routine UTI
practicetest your knowledge on urinary tract infections (complicated, catheter-associated)Apply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — infectious diseases and beyond.
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