What is the appropriate management for a patient with a urine culture showing polymicrobic growth, probable skin contamination, and a colony count of less than 10,000 colonies/mL?

Management of Polymicrobic Urine Culture with <10,000 CFU/mL

Do not treat this result—it represents contamination, not infection, and requires no antimicrobial therapy. 1

Understanding This Result

Polymicrobic growth with colony counts below 10,000 CFU/mL indicates specimen contamination from periurethral, vaginal, or perineal flora rather than true urinary tract infection. 1 The presence of multiple bacterial species strongly suggests contamination, particularly when accompanied by low colony counts and epithelial cells on urinalysis. 1

Clinical Decision Algorithm

Step 1: Assess Collection Method

• If collected by bag or non-clean catch method: This result is highly unreliable and should be disregarded. 1
• If collected by catheterization: While more reliable than bag collection, polymicrobic growth still indicates contamination. 1
• If collected by suprapubic aspiration: Any growth would be significant, but polymicrobic growth is extremely rare with this method. 1

Step 2: Review Urinalysis Findings

• Check for pyuria (≥10 WBCs/HPF or ≥10 WBCs/mm³): Absence of pyuria strongly suggests contamination rather than infection. 1
• Check for bacteriuria on microscopy: True infection requires both pyuria AND bacteriuria. 2
• Evaluate leukocyte esterase and nitrites: Negative dipstick results with polymicrobic growth confirm contamination. 1

Step 3: Correlate with Clinical Presentation

• If patient is asymptomatic: No further action needed—this is contamination. 1
• If patient has UTI symptoms (dysuria, urgency, frequency, fever): Recollect specimen using proper technique before considering treatment. 1

Diagnostic Criteria for True UTI (When to Recollect)

For febrile infants and children (2-24 months), true UTI requires BOTH: 2

• Urinalysis showing pyuria and/or bacteriuria
• ≥50,000 CFU/mL of a single uropathogen from catheterized specimen

For adults with acute pyelonephritis, true infection requires: 2

• 10,000 CFU/mL of a uropathogen

• Clinical symptoms (fever, flank pain)
• Pyuria on urinalysis

When to Recollect the Specimen

Recollect using catheterization or suprapubic aspiration if: 1

• Patient has persistent fever without source (especially infants <24 months)
• Strong clinical suspicion for UTI based on symptoms
• Urinalysis shows pyuria (≥10 WBCs/HPF) despite polymicrobic culture

Do NOT recollect if: 1

• Patient is asymptomatic
• Urinalysis is negative for pyuria and bacteriuria
• Clinical suspicion for UTI is low

Critical Pitfalls to Avoid

Never treat polymicrobic growth from bag specimens without confirmation by catheterization. 1 Bag collection has contamination rates of 65-68%, making positive results unreliable. 1

Do not assume heavy mixed growth rules out infection. 1 While rare, heavy mixed growth may occasionally mask a true pathogen, requiring recollection if clinical suspicion remains high. 1

Avoid using outdated colony count thresholds. 1 The threshold of ≥50,000 CFU/mL (not 100,000 CFU/mL) is now standard for catheterized specimens in febrile children. 2

Do not treat based on culture alone without urinalysis correlation. 2 Bacteriuria without pyuria represents asymptomatic bacteriuria or contamination, not infection requiring treatment.

Proper Collection Technique for Future Specimens

To reduce contamination rates: 1

• Cleanse the perineal area before collection (reduces contamination from 23.9% to 7.8%)
• Use catheterization for most reliable results (contamination rate 4.7% vs. 27% for clean-catch)
• Discard the first few milliliters when catheterizing, then collect subsequent urine
• Process specimen within 1 hour or refrigerate immediately