How do you treat a urinary tract infection (UTI) caused by Staphylococcus aureus?

Treatment of Urinary Tract Infection Caused by Staphylococcus aureus

For urinary tract infections caused by Staphylococcus aureus, vancomycin is the first-line treatment for methicillin-resistant strains (MRSA), while antistaphylococcal penicillins or first-generation cephalosporins are recommended for methicillin-susceptible strains (MSSA). 1

Initial Assessment and Considerations

• S. aureus in urine is often associated with:

  • Recent urinary catheterization (82% of cases) 2
  • Symptomatic UTI (33% of cases) 2
  • Risk of concurrent bacteremia (13% of cases) 2

• Always obtain blood cultures when S. aureus is isolated from urine to rule out concurrent bacteremia

• Determine methicillin susceptibility status (MRSA vs. MSSA) before selecting definitive therapy

Treatment Algorithm

For MRSA UTI:

1. First-line options:

   • Vancomycin 30-60 mg/kg/day IV divided in 2-4 doses 3, 1
   • Teicoplanin 6-12 mg/kg/dose IV q12h for three loading doses, then daily 3

2. Alternative options:

   • Linezolid 600 mg IV/PO q12h 1
   • Daptomycin 4-6 mg/kg IV daily (avoid in pneumonia due to reduced lung penetration) 1, 4
   • TMP-SMX 160-320/800-1600 mg PO q12h (for uncomplicated cases) 3

For MSSA UTI:

1. First-line options:

   • Nafcillin or oxacillin IV 1
   • Cefazolin IV 1
   • Dicloxacillin PO (for uncomplicated cases) 1
   • Cephalexin PO (for uncomplicated cases) 1

2. Alternative options for penicillin-allergic patients:

   • Clindamycin (if local resistance <10%) 1
   • Doxycycline 100 mg PO q12h 3

Treatment Duration

• Uncomplicated lower UTI: 7-14 days
• Complicated UTI/pyelonephritis: 14 days
• UTI with concurrent bacteremia:
  • Uncomplicated bacteremia: minimum 14 days 1
  • Complicated bacteremia: 4-6 weeks 1

Special Considerations

1. Catheter management:

   • Remove or replace urinary catheters if present
   • S. aureus UTIs are strongly associated with catheterization 2

2. Monitoring:

   • Repeat blood cultures to document clearance if initial cultures were positive
   • Monitor renal function, especially with vancomycin therapy
   • Watch for signs of metastatic infection (endocarditis, osteomyelitis)

3. Persistent or relapsing infection:

   • Repeat blood cultures and susceptibility testing 1
   • Rule out sequestered foci of infection 1
   • Consider surgical intervention if appropriate 1
   • Consider changing antimicrobial regimen if treatment failure occurs 1

4. Renal impairment:

   • Adjust dosing based on creatinine clearance
   • Clinical success rates with daptomycin are lower in patients with baseline CrCl <50 mL/min 5
   • Monitor for tubulointerstital nephritis with daptomycin 5

Pitfalls and Caveats

1. S. aureus in urine is rarely a contaminant and should be treated as a true infection, especially in catheterized patients 2

2. Risk of subsequent bacteremia: S. aureus bacteriuria can lead to subsequent invasive infection up to 12 months after initial isolation 2

3. Vancomycin monitoring: Therapeutic drug monitoring is essential to ensure adequate dosing while minimizing nephrotoxicity

4. Daptomycin cautions:

   • Monitor CPK weekly due to risk of myopathy and rhabdomyolysis 5
   • Watch for eosinophilic pneumonia 5
   • Not recommended for patients younger than 12 months 5

5. Antibiotic resistance: 86% of urinary S. aureus isolates in long-term care settings are MRSA 2, necessitating appropriate empiric coverage while awaiting susceptibility results