Should I treat with antibiotics a urine culture showing Proteus Mirabilis (a type of bacteria) >100,000 Colony-Forming Units per Milliliter (CFU/ML) in an asymptomatic patient with an indwelling (dwelling) Foley (urinary) catheter?

Do Not Treat Asymptomatic Bacteriuria in Catheterized Patients

You should NOT treat this patient with antibiotics. The 2019 IDSA guidelines provide a strong recommendation against screening for or treating asymptomatic bacteriuria (ASB) in patients with indwelling urinary catheters, regardless of whether the catheter is short-term (<30 days) or long-term 1.

Why Treatment is Not Indicated

Universal Bacteriuria is Expected

• All patients with indwelling catheters ultimately develop bacteriuria due to biofilm formation along the catheter surface 1
• Bacteriuria acquisition occurs at a rate of 3-5% per catheter day 1
• The presence of >100,000 CFU/mL of Proteus mirabilis in your patient represents colonization, not infection 2, 3

Low Risk of Complications

• Only 7.7% of catheterized patients with bacteriuria develop any subjective symptoms 1
• Bacteremia directly attributable to catheter-associated bacteriuria occurs in only 0.5-0.7% of cases 1
• Short-term catheter-associated bacteriuria does not increase risk for sepsis or death 1

Harms of Treatment Outweigh Benefits

• Antimicrobial therapy only temporarily suppresses bacteriuria; recurrence with the same or different (often more resistant) organisms occurs universally 1
• Treatment promotes emergence of antimicrobial-resistant organisms without effectively clearing the urine 3, 4
• Risk of Clostridioides difficile infection is substantial in hospitalized patients receiving unnecessary antibiotics 1
• Studies show that 32-52% of catheterized patients with asymptomatic bacteriuria are inappropriately treated with antibiotics 5, 6

Clinical Algorithm for Decision-Making

Step 1: Assess for Symptoms

Look for these specific signs/symptoms that would indicate true catheter-associated UTI (CAUTI) rather than ASB:

• Fever without another identified source 1, 7
• Acute costovertebral angle pain or tenderness 1
• Suprapubic pain or tenderness 1
• Acute hematuria 1
• Hemodynamic instability or signs of sepsis 1

If none of these are present → Do not treat 1

Step 2: Consider Special Circumstances

Treatment may be warranted ONLY in these specific situations:

• Planned urologic procedure with anticipated mucosal bleeding (e.g., transurethral resection of prostate) 1, 2
• Pregnancy (not applicable to your patient) 2
• High-risk neutropenia (absolute neutrophil count <100 cells/mm³, ≥7 days duration) 1

Step 3: Management Strategy

For your asymptomatic catheterized patient:

• Do not initiate antibiotics 1
• Consider catheter removal if medically appropriate, as this may clear bacteriuria in approximately 40% of patients 7
• If catheter removal is planned, there is a knowledge gap regarding treatment of ASB 48 hours post-removal; one option is to consider treatment only if bacteriuria persists 48 hours after catheter removal 1, 2

Common Pitfalls to Avoid

Pitfall #1: Treating Based on Colony Count Alone

• The presence of >100,000 CFU/mL does not distinguish infection from colonization in catheterized patients 1, 2
• Even high bacterial counts in asymptomatic patients should not trigger treatment 1, 6

Pitfall #2: Treating Based on Pyuria

• Pyuria accompanying asymptomatic bacteriuria is NOT an indication for antimicrobial treatment 2
• Studies show that higher urine white blood cell counts inappropriately influence clinicians to treat ASB 6

Pitfall #3: Treating Gram-Negative Organisms More Aggressively

• Clinicians are more likely to inappropriately treat gram-negative bacteriuria (like your Proteus mirabilis) compared to other organisms 6
• The organism type should not change management in asymptomatic patients 6

Pitfall #4: Ordering Unnecessary Cultures

• Avoid screening urine cultures in asymptomatic catheterized patients 7, 2
• Cultures should only be obtained when clinical symptoms suggest infection 1

Evidence Quality and Strength

The recommendation against treatment is based on:

• Strong recommendation from the 2019 IDSA guidelines (the most recent and authoritative source) 1
• Multiple prospective studies showing no mortality benefit from treatment 1
• A randomized controlled trial of 60 ICU patients showing no difference in mortality, recurrent bacteriuria, or mechanical ventilation duration between treated and untreated groups 1
• Consistent evidence that treatment leads to resistant organisms without clinical benefit 1, 3, 4

The evidence strongly supports withholding antibiotics in your patient, prioritizing avoidance of antimicrobial resistance and adverse drug effects over treating a benign colonization 1, 2.