What are the differential diagnoses and initial management for a patient presenting with symptoms of a Urinary Tract Infection (UTI)?

Differential Diagnoses for UTI

When evaluating a patient with suspected UTI symptoms, consider alternative diagnoses including urethritis, vaginitis, pyelonephritis, prostatitis (in men), interstitial cystitis, and asymptomatic bacteriuria—each requiring distinct diagnostic and management approaches.

Key Diagnostic Distinctions

Uncomplicated vs. Complicated UTI

• Uncomplicated UTI presents with dysuria, frequency, urgency, or suprapubic pain in otherwise healthy, non-pregnant women without anatomical/functional urinary tract abnormalities 1
• Complicated UTI includes any infection beyond the bladder (pyelonephritis), presence of anatomical/functional abnormalities, immunocompromise, pregnancy, male gender, or catheter-associated infections 1, 2

Pyelonephritis (Upper Tract Infection)

• Distinguished by fever, flank pain, costovertebral angle tenderness, often with nausea and vomiting 1
• Represents tissue invasion requiring more aggressive treatment than simple cystitis 3, 4

Urethritis

• Consider in patients with dysuria but without frequency or urgency 2
• More common in men and sexually active individuals; may present with urethral discharge 2
• Requires different antimicrobial coverage (often for sexually transmitted pathogens) 2

Prostatitis (Men Only)

• Presents with dysuria, frequency, urgency, plus perineal/pelvic pain, obstructive voiding symptoms 2
• May include fever and systemic symptoms in acute bacterial prostatitis 2
• Requires longer antibiotic courses (typically weeks) compared to simple cystitis 5

Vaginitis/Cervicitis (Women)

• Vaginal discharge or irritation suggests alternative diagnosis to UTI 1, 5
• Self-diagnosis of UTI in women with typical symptoms without vaginal discharge is sufficiently accurate to proceed with treatment 5

Asymptomatic Bacteriuria (ASB)

• Positive urine culture without UTI symptoms 1, 2
• Should NOT be treated in most populations except pregnant women and patients undergoing urologic procedures 1, 6
• Common pitfall: treating positive cultures in catheterized or elderly patients without symptoms leads to unnecessary antibiotic use 1

Initial Diagnostic Approach

Clinical Diagnosis

• In healthy non-pregnant women with typical symptoms (dysuria, frequency, urgency) and no vaginal discharge, clinical diagnosis alone is sufficient to initiate treatment without urinalysis or culture 5
• Pyuria is usually present with true UTI; absence of pyuria suggests alternative diagnosis 1, 3

When to Obtain Urine Culture

Obtain culture in these situations:

• Recurrent infections 1, 5
• Treatment failure 1, 5
• History of resistant organisms 1
• Atypical presentation 1, 5
• All men with UTI symptoms 5
• Suspected pyelonephritis 1
• Complicated UTI 1, 2
• Adults ≥65 years 5

Pediatric Considerations (2-24 months)

• UTI should be considered in any febrile infant 2-24 months with unexplained fever (prevalence ~5%) 1
• Diagnosis requires both pyuria AND ≥50,000 CFU/mL of single uropathogen in properly collected specimen 1, 7
• Never use bag specimens for culture—only catheterization or suprapubic aspiration 1, 7
• Organisms like Lactobacillus, coagulase-negative staphylococci, and Corynebacterium are not clinically relevant isolates 1

Initial Management by Category

Uncomplicated Cystitis (Women)

First-line antibiotics (choose based on local resistance patterns): 1, 5

• Nitrofurantoin 100 mg BID × 5 days
• Fosfomycin 3g single dose
• Trimethoprim 100 mg BID × 3 days
• Trimethoprim-sulfamethoxazole DS BID × 3 days

Treatment duration: As short as reasonable, generally no longer than 7 days for cystitis 1

Uncomplicated Cystitis (Men)

• Always obtain urine culture before treatment 5
• First-line: Trimethoprim, TMP-SMX, or nitrofurantoin × 7 days (longer than women) 5
• Consider urethritis and prostatitis in differential 5

Acute Pyelonephritis

• Requires 7-14 days of antimicrobial therapy depending on agent and severity 1
• Fluoroquinolones historically first-line for oral therapy, but resistance increasing 3
• Nitrofurantoin should NOT be used for pyelonephritis—inadequate tissue/serum concentrations 1, 7, 3

Febrile UTI in Infants (2-24 months)

Parenteral therapy indicated if: 1, 7

• Appears toxic
• Unable to retain oral fluids/medications
• Uncertain compliance

Parenteral options: 1, 7

• Ceftriaxone 75 mg/kg every 24 hours
• Cefotaxime 150 mg/kg/day divided every 6-8 hours

Oral options (for stable infants): 1, 7

• Amoxicillin-clavulanate 20-40 mg/kg/day in 3 doses
• Cephalosporins (cefixime, cefpodoxime, cephalexin)

Duration: 7-14 days 1

Critical Pitfalls to Avoid

Diagnostic Stewardship

• Do NOT routinely obtain urine cultures for fever workup in hospitalized patients without urinary symptoms—leads to unnecessary treatment of ASB 1
• Do NOT treat ASB except in pregnant women or pre-urologic procedure patients 1, 6
• Routine cystoscopy and upper tract imaging should NOT be obtained in index patient with recurrent UTI 1

Pediatric-Specific Pitfalls

• Do NOT delay neurologic evaluation in children with urinary retention if no obvious obstructive/infectious cause identified (17% have underlying neurologic pathology) 7
• Renal/bladder ultrasound should be performed after confirmed febrile UTI to detect anatomical abnormalities 1, 7
• VCUG NOT recommended routinely after first UTI; reserve for hydronephrosis, scarring, recurrent febrile UTI, or atypical circumstances 1

Antimicrobial Resistance Considerations

• Know local antibiogram patterns—resistance to TMP-SMX and fluoroquinolones varies substantially by region 1, 3
• Avoid broad-spectrum agents when narrow-spectrum options effective 1
• Culture-directed therapy essential for resistant organisms 1