What is the treatment for a urine culture positive for Staphylococcus (Staph) aureus?

Treatment of Staphylococcus aureus in Urine

Asymptomatic S. aureus bacteriuria should NOT be treated in most patients, as it typically represents contamination or colonization that does not warrant antimicrobial therapy. 1

Initial Clinical Assessment

Determine if the patient is symptomatic or asymptomatic:

• Asymptomatic bacteriuria (no fever, dysuria, flank pain, or urinary symptoms) should not be treated, as treatment increases antimicrobial resistance, costs, and adverse effects without improving outcomes 1
• Symptomatic UTI (fever, dysuria, flank pain, or other urinary symptoms) with properly collected urine culture showing ≥50,000 CFU/mL of S. aureus as a single pathogen requires treatment 1

Critical Risk Stratification: Rule Out Bacteremia

S. aureus bacteriuria may represent hematogenous seeding from bacteremia rather than primary UTI, which carries significantly higher mortality. 2, 3

Obtain blood cultures in high-risk patients:

• Patients with persistent fever or systemic signs of infection 4, 5
• Those with urological instrumentation or recent procedures 4, 2
• Patients with indwelling urinary catheters (82% of S. aureus bacteriuria cases have recent catheterization) 2
• Presence of metastatic infection symptoms (back pain, joint pain, altered mental status) 5

Key evidence: Among patients with S. aureus bacteriuria who had blood cultures drawn, 6.5% had concurrent bacteremia, with 4 of 6 cases associated with urological instrumentation 4. Patients with both bacteremia and bacteriuria have 3-fold higher mortality (39% vs 17%) compared to bacteremia alone 3.

When Treatment IS Indicated

For Symptomatic UTI (No Bacteremia)

Targeted antimicrobial therapy based on susceptibility testing:

• For MSSA: Cefazolin or antistaphylococcal penicillins (nafcillin, oxacillin) 1, 6, 5
• For MRSA: Vancomycin or daptomycin 1, 6, 5
• If penicillin allergy (MSSA): Ciprofloxacin or clindamycin 1

Duration of therapy:

• 7 days for prompt symptom resolution 1
• 10-14 days for delayed response 1

For Catheter-Associated S. aureus Bacteriuria

Replace the catheter if it has been in place ≥2 weeks before starting antimicrobial therapy, as antibiotic therapy alone will likely fail due to biofilm formation. 1

Clinical context: 86% of initial S. aureus urine isolates in long-term care patients are MRSA, and 58% have persistent bacteriuria lasting a median of 4.3 months 2. Device removal is often necessary for device-related infections due to biofilm formation 7.

If S. aureus Bacteremia is Confirmed

This changes management dramatically:

• Obtain transesophageal echocardiography for high-risk patients (persistent bacteremia ≥48 hours, persistent fever, metastatic infection foci, or implantable cardiac devices) 1, 5
• Duration of therapy: Minimum 14 days if uncomplicated; 4-6 weeks if complicated or endocarditis is present 1, 5
• Source control is critical: Remove infected intravascular or implanted devices, drain abscesses, perform surgical debridement as needed 5

Rationale: Prolonged S. aureus bacteremia (≥48 hours) is associated with 90-day mortality risk of 39%, and metastatic infection occurs in more than one-third of cases 5. Late-onset staphylococcal infections can occur up to 12 months after initial isolation, with 5 of 8 late blood isolates matching the initial urine isolate by molecular typing 2.

Special Circumstances Requiring Treatment

Pre-Procedure Prophylaxis

Screen for and treat asymptomatic S. aureus bacteriuria only before endoscopic urologic procedures with mucosal trauma (TURP, ureteroscopy, lithotripsy):

• Use 1-2 doses of targeted antimicrobial administered 30-60 minutes before the procedure 1

Pregnancy

Treat asymptomatic bacteriuria in pregnant women, one of the few populations where asymptomatic bacteriuria requires treatment. 7

Monitoring and Follow-Up

Assess clinical response within 48-72 hours and adjust antibiotics based on culture and susceptibility results. 1

Consider repeat urine culture in high-risk patients:

• Urinary catheterization 4
• Urological abnormality 4
• Diabetes 4
• Inpatient status 4

Common Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria in well patients without high-risk features or upcoming urologic procedures 1, 4
• Do not assume S. aureus in urine is always a primary UTI – it may represent hematogenous seeding from occult bacteremia, which requires different management 2, 3
• Do not use vancomycin for routine prophylaxis or for treating presumed infections when cultures are negative 7
• Do not forget to ensure proper specimen collection technique to minimize contamination, as S. aureus can be normal skin flora 7