What is the best management approach for a 2-year-old pediatric patient with non-resolving Aerococcus urinae infection despite treatment with amoxicillin (amoxicillin)?

Management of Aerococcus urinae UTI with Amoxicillin Failure in a 2-Year-Old

Switch to amoxicillin-clavulanate at high-dose (90 mg/kg/day of the amoxicillin component divided into 2 doses) for 7-14 days, as this provides β-lactamase coverage that may be needed for treatment failure while maintaining activity against Aerococcus urinae. 1, 2

Immediate Management Steps

Obtain Culture and Susceptibility Testing

• Send a repeat urine culture with specific instructions to incubate in a CO2-containing atmosphere, as Aerococcus species require this environment for optimal growth and may be missed with standard culture techniques 3
• Request antimicrobial susceptibility testing to guide definitive therapy, as treatment recommendations for Aerococcus urinae are primarily based on in vitro susceptibility patterns 4

Switch Antibiotic Therapy

• Escalate to amoxicillin-clavulanate (co-amoxiclav) at 90 mg/kg/day of the amoxicillin component divided into 2 doses for a 2-year-old with treatment failure 1, 2
• The β-lactamase inhibitor component addresses potential resistance mechanisms while maintaining coverage for Aerococcus urinae 2
• Alternative dosing of 45 mg/kg/day divided into 3 doses is acceptable but twice-daily dosing at the higher dose improves compliance 1
• Maximum daily dose should not exceed 4000 mg of amoxicillin 1

Treatment Duration

• Treat for 7-14 days total, as recommended by the American Academy of Pediatrics for pediatric UTIs 1
• Shorter courses (1-3 days) are inferior for febrile UTIs and should be avoided 1
• While one case report showed success with 3 days of amoxicillin for uncomplicated Aerococcus urinae infection, this was in a patient without treatment failure 5

Alternative Antibiotic Options Based on Susceptibility

If Amoxicillin-Clavulanate Fails or Is Not Tolerated

• Nitrofurantoin achieved clinical and microbiological success in 71%/76% of Aerococcus urinae UTI cases in adults, making it a reasonable alternative for cystitis (not pyelonephritis) 4
• However, nitrofurantoin is inadequate for febrile UTI/pyelonephritis as it only achieves urinary concentrations 2
• Pivmecillinam showed success in Aerococcus urinae cystitis cases 4
• Ciprofloxacin was effective for pyelonephritis cases in the adult literature 4, though fluoroquinolones are generally avoided in pediatrics due to musculoskeletal safety concerns 2

For Severe or Invasive Infection

• If the child appears toxic or has signs of pyelonephritis, consider parenteral therapy with ceftriaxone (50 mg/kg/dose every 24 hours) until clinical improvement occurs, typically within 24-48 hours 6, 1
• For serious Aerococcus urinae infections, penicillin or ampicillin combined with an aminoglycoside has been recommended based on adult case series 7
• One case of spondylodiscitis was successfully treated with amoxicillin for extended duration 8

Critical Evaluation Steps

Assess for Underlying Urological Abnormalities

• Obtain a renal ultrasound to evaluate for anatomic abnormalities, as recommended for first febrile UTI in children <3 years 2
• The one pediatric case report of Aerococcus urinae UTI revealed underlying bilateral mild to moderate hydronephrosis 5
• Aerococcus urinae infections typically occur in patients with underlying urinary tract disorders 3, 7

Clinical Reassessment

• Reassess at 24-48 hours to confirm fever resolution and clinical improvement 2
• Adjust antibiotics based on culture results and susceptibilities when available 2
• If symptoms persist beyond 48-72 hours on appropriate therapy, consider imaging to evaluate for complications such as renal abscess

Important Caveats

Avoid These Common Pitfalls

• Do not use azithromycin or other macrolides, as they have inadequate coverage for common UTI pathogens and increasing resistance patterns 2
• Do not use oral third-generation cephalosporins as monotherapy due to pneumococcal resistance patterns, though they may be considered as alternatives (cefixime 8 mg/kg/day, cefpodoxime 10 mg/kg/day divided into 2 doses) 1, 6
• Do not assume standard urine culture techniques will detect Aerococcus species - specifically request CO2 incubation 3

Special Considerations for This Age Group

• At age 2, the child is old enough that observation without antibiotics is not appropriate once bacterial UTI is confirmed 6
• Local antimicrobial sensitivity patterns should guide empiric therapy choices 1
• The rarity of Aerococcus urinae in pediatrics (only a few case reports exist) means treatment recommendations are extrapolated from adult data and in vitro susceptibility testing 5, 4