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, 2
Initial Assessment and Risk Stratification
Determine if the patient is symptomatic or asymptomatic:
- Asymptomatic bacteriuria (no fever, dysuria, flank pain, or suprapubic pain) should NOT be treated in the vast majority of cases, as treatment increases antimicrobial resistance, costs, and adverse drug effects without improving outcomes 1
- Symptomatic UTI (fever, dysuria, flank pain, or other UTI symptoms) with properly collected urine culture showing ≥50,000 CFU/mL of S. aureus as a single pathogen requires treatment 1
Assess for invasive S. aureus disease risk:
- Patients with MRSA bacteriuria (vs MSSA) have significantly higher risk of invasive disease (22.3% vs 8.4%, OR 2.91) 3
- Absence of UTI symptoms paradoxically increases risk of invasive disease (OR 3.21), suggesting bacteremic seeding rather than primary UTI 3
- Absence of pyuria is associated with worse outcomes including death (OR 2.00) 3
- Inpatient status increases risk of invasive disease (OR 4.72) and death (OR 3.62) 3
Obtain blood cultures in high-risk patients:
- MRSA bacteriuria 3
- Absence of UTI symptoms (suggesting hematogenous seeding) 2, 3
- Absence of pyuria 3
- Inpatient status 3
- Prior to urological instrumentation 2
- Recent urological procedures 2
When Treatment IS Indicated
Symptomatic UTI with Confirmed S. aureus
Use targeted antimicrobial therapy based on susceptibility testing: 1
- For MSSA: Cefazolin or antistaphylococcal penicillins (flucloxacillin, dicloxacillin) are first-line 4, 5
- For MRSA: Vancomycin or daptomycin 5
- Alternative for MSSA if penicillin allergy: Ciprofloxacin (for non-immediate hypersensitivity) or clindamycin (if local resistance <10%) 1, 4
Duration of therapy:
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
Pre-Procedure Prophylaxis
Screen for and treat asymptomatic S. aureus bacteriuria ONLY before endoscopic urologic procedures with mucosal trauma (TURP, ureteroscopy, lithotripsy): 1
- Use 1-2 doses of targeted antimicrobial administered 30-60 minutes before the procedure 1
When S. aureus Bacteremia is Confirmed
If blood cultures are positive for S. aureus, this is NOT a urinary tract infection but rather bacteremic seeding of the urinary tract, requiring management as S. aureus bacteremia: 5, 3
- All patients require transthoracic echocardiography 5
- Transesophageal echocardiography for high-risk patients (persistent bacteremia ≥48 hours, persistent fever, metastatic infection foci, implantable cardiac devices) 6, 5
- For MSSA bacteremia: Cefazolin or antistaphylococcal penicillins 5
- For MRSA bacteremia: Vancomycin or daptomycin 5
- Duration: Minimum 14 days if uncomplicated; 4-6 weeks if complicated or endocarditis present 6, 5
- Source control is critical (remove infected intravascular devices, drain abscesses) 5
Monitoring and Follow-Up
Consider repeat urine culture in high-risk patients: 2
Assess clinical response within 48-72 hours and adjust antibiotics based on culture and susceptibility results. 1
Common Pitfalls to Avoid
- Do not routinely treat asymptomatic S. aureus bacteriuria in well patients, as this increases resistance without benefit 1, 2
- Do not assume S. aureus bacteriuria is always a primary UTI—it may represent bacteremic seeding from another source, particularly in asymptomatic patients without pyuria 2, 3
- Do not fail to obtain blood cultures in high-risk patients (MRSA, asymptomatic, no pyuria, inpatient), as 22.3% of MRSA bacteriuria cases have invasive disease 3
- Do not treat catheter-associated S. aureus bacteriuria without replacing catheters ≥2 weeks old, as biofilm will cause treatment failure 1