What are the next steps for a patient with a urinary tract infection (UTI) caused by Enterococcus sensitive to amoxicillin, who has a slow rise in white blood cell (WBC) count after initiating amoxicillin therapy?

Management of Rising WBC in a Patient with Enterococcus UTI on Amoxicillin

For a patient with Enterococcus UTI showing a rising WBC count despite amoxicillin treatment (to which the organism is sensitive), further diagnostic investigation is warranted as this suggests inadequate source control or a more complicated infection.

Initial Assessment

When faced with a rising WBC count in a patient with Enterococcus UTI on appropriate antibiotic therapy, consider:

• Duration of current therapy: Treatment should continue for a minimum of 5-7 days for uncomplicated UTIs, and 10-14 days for complicated infections 1
• Adequacy of dosing: Ensure amoxicillin dosing is appropriate (500mg every 8 hours) 2
• Signs of clinical deterioration: Assess for fever, flank pain, or systemic symptoms

Diagnostic Workup

Immediate Investigations:

1. Repeat urinalysis and urine culture:

   • Check for persistent pyuria (≥10 WBCs/high-power field)
   • Confirm ongoing Enterococcus infection or superinfection 3

2. Blood cultures:

   • Indicated if bacteremia/urosepsis is suspected
   • Paired with urine culture if patient has systemic symptoms 3

3. Imaging studies:

   • Renal ultrasound or CT scan to evaluate for:
     • Urinary obstruction
     • Renal/perinephric abscess
     • Emphysematous pyelonephritis
     • Anatomical abnormalities

Consider Additional Testing:

• Complete blood count with differential: To confirm leukocytosis and assess for left shift 3
• Renal function tests: To evaluate kidney function and adjust antibiotic dosing if needed
• Inflammatory markers: C-reactive protein or procalcitonin to assess severity

Management Approach

If Uncomplicated UTI with Inadequate Response:

1. Extend amoxicillin treatment duration to 10-14 days 1
2. Consider alternative antibiotic therapy if culture shows resistance development:
   • Nitrofurantoin 100mg twice daily (for lower UTI)
   • Fosfomycin 3g single dose (for lower UTI)
   • Parenteral therapy for systemic symptoms 1

If Complicated Infection Suspected:

1. Broaden antibiotic coverage pending cultures:

   • Consider adding an aminoglycoside if pyelonephritis or urosepsis is suspected 3
   • For severe infections, consider parenteral therapy with ampicillin or vancomycin 3

2. Evaluate for source control issues:

   • Urinary obstruction requiring drainage
   • Abscess requiring drainage
   • Infected stones or foreign body

If Concern for Alternative Diagnosis:

1. Consider infective endocarditis if patient has:

   • Persistent bacteremia
   • New heart murmur
   • Embolic phenomena
   • Predisposing cardiac conditions 3

2. Evaluate for intra-abdominal infection if patient has:

   • Abdominal pain
   • Abnormal liver function tests
   • Risk factors for biliary disease 3

Key Considerations

• Patients with ongoing signs of infection beyond 7 days of antibiotic treatment warrant diagnostic investigation 3
• Enterococcal UTIs with rising WBC may represent complicated infections requiring longer treatment courses or alternative antibiotics
• Consider infectious disease consultation for persistent or complicated enterococcal infections 1
• Enterococcal bacteremia has significant mortality (16.5%) and requires aggressive management 4

Common Pitfalls to Avoid

• Failing to investigate for complications: Rising WBC despite appropriate antibiotic therapy suggests a complication requiring further workup
• Inadequate source control: Ensure no urinary obstruction or abscess is present
• Missing disseminated infection: Consider endocarditis or other metastatic foci in persistent enterococcal infections
• Continuing ineffective therapy: If clinical deterioration occurs, broaden coverage while awaiting culture results

The rising WBC count in your patient with Enterococcus UTI on amoxicillin therapy is concerning for treatment failure and requires prompt evaluation for complications or alternative diagnoses.