Should a repeat urine culture be performed when the admission urine culture grows Staphylococcus aureus that is sensitive to trimethoprim‑sulfamethoxazole (Bactrim), vancomycin, and gentamicin, and resistant to other agents?

Should You Repeat the Urine Culture?

No, you should not routinely repeat the urine culture in this case. The initial culture has already identified Staphylococcus aureus with clear sensitivities to appropriate antibiotics (Bactrim, vancomycin, gentamicin), and repeat cultures after starting appropriate antimicrobial therapy have extremely low yield and are not cost-effective.

Clinical Context and Decision Framework

When S. aureus is Found in Urine

First, determine if this represents true urinary tract infection versus asymptomatic bacteriuria or contamination:

• If the patient has UTI symptoms (dysuria, frequency, urgency, fever, flank pain): This is a true UTI requiring treatment
• If the patient is asymptomatic: This may represent asymptomatic bacteriuria, which generally does not require treatment 1
• Critical consideration: S. aureus bacteriuria can be a marker of occult S. aureus bacteremia, particularly in hospitalized patients 2. You should evaluate for other sources of S. aureus infection (endocarditis, osteomyelitis, abscess)

Evidence Against Routine Repeat Cultures

The data strongly argues against repeating urine cultures during treatment:

• Pediatric data shows only 0.3% positive repeat cultures after 2 days of appropriate antibiotics 3
• Another study found 9.2% positive repeat cultures, but these were associated with specific risk factors: age <1 year, Enterococcus (not S. aureus), fever >72 hours, inappropriate antibiotics, or urinary tract anomalies 4
• Repeat cultures inflate resistance statistics without clinical benefit, particularly in hospitalized patients 5

When You SHOULD Consider Repeat Culture

Repeat culture is indicated only if:

• Clinical failure: Persistent fever or symptoms after 48-72 hours of appropriate therapy
• Inappropriate initial antibiotic choice: If empiric therapy was not covering the organism (not your case—you have sensitivities)
• Complicated UTI: Urinary tract obstruction, abscess, or anatomic abnormalities
• Concern for bacteremia: If blood cultures are positive or clinical picture suggests disseminated infection

Treatment Recommendations

Given your sensitivities, appropriate treatment options include:

For uncomplicated UTI:

• Trimethoprim-sulfamethoxazole (Bactrim) is highly effective for S. aureus UTI with 91-95% susceptibility rates 2, 6 and is FDA-approved for UTI treatment 7
• Oral therapy is appropriate if the patient can tolerate it

For complicated UTI or bacteremia:

• Vancomycin IV if MRSA or severe infection 8
• Gentamicin IV is effective but has nephrotoxicity concerns; reserve for serious infections 8

Common Pitfalls to Avoid

1. Don't assume S. aureus in urine is always just a UTI: Rule out bacteremia, especially if the patient has risk factors (IV drug use, indwelling catheters, recent hospitalization, endocarditis risk factors)
2. Don't order "test of cure" cultures: These are not indicated for uncomplicated UTI and waste resources 3
3. Don't continue antibiotics beyond standard duration just because the organism is S. aureus—treat like other UTIs unless complicated

Bottom Line Algorithm

1. Assess clinical response at 48-72 hours (fever resolution, symptom improvement)
2. If improving clinically: Continue antibiotics, no repeat culture needed
3. If not improving: Consider repeat culture AND evaluate for alternative source of S. aureus (blood cultures, imaging for abscess/endocarditis)
4. Complete appropriate duration: 7-14 days depending on severity and clinical response

The initial culture has given you actionable information with clear sensitivities. Clinical assessment of treatment response is far more valuable than routine repeat cultures 4, 3.