What does the presence of beta-hemolytic streptococcus (Group B streptococcus) group B with a colony count of 25,000 to 50,000 Colony-Forming Units per milliliter (CFU/mL) in a urine culture indicate?

Group B Streptococcus (GBS) Bacteriuria at 25,000-50,000 CFU/mL

A colony count of 25,000-50,000 CFU/mL of Group B Streptococcus in urine represents clinically significant bacteriuria that requires treatment, particularly in pregnant women, and warrants intrapartum antibiotic prophylaxis regardless of the colony count. 1

Clinical Significance

For pregnant women specifically:

• Any colony count of GBS in urine during pregnancy is an indication for intrapartum antibiotic prophylaxis, as GBS bacteriuria at any concentration is a marker for heavy genital tract colonization and increases the risk of early-onset neonatal GBS disease. 1
• The CDC guidelines since 2002 recommend reporting GBS present in any concentration in urine, moving away from requiring the traditional ≥100,000 CFU/mL threshold. 1
• Women with documented GBS bacteriuria at any level should receive appropriate intravenous antibiotics during labor or after rupture of membranes to prevent early-onset neonatal disease. 2
• GBS bacteriuria occurs in 2-7% of pregnant women and is associated with increased risk for early-onset disease in newborns. 1

For non-pregnant adults:

• Colony counts between 25,000-50,000 CFU/mL may represent significant infection, especially when obtained via catheterization, where counts as low as 10,000 CFU/mL can be clinically significant. 3
• GBS accounts for approximately 2% of positive urine cultures in non-pregnant adults and should not be dismissed as a contaminant. 4
• The presence of a single organism (GBS alone) rather than mixed flora supports true infection rather than contamination. 3

Interpretation Context

Key factors affecting clinical significance:

• Collection method matters: Catheterized specimens have lower thresholds for significance (≥10,000 CFU/mL) compared to clean-catch specimens. 3
• Clinical presentation: Interpretation must consider presence of pyuria, bacteriuria on urinalysis, and urinary symptoms. 3
• Patient characteristics: 85% of non-pregnant adults with GBS bacteriuria are women, and 95% have underlying conditions such as urinary tract abnormalities (60%) or chronic renal failure (27%). 4

Management Approach

For pregnant women:

• Treat with appropriate antibiotics if symptomatic or if colony count ≥100,000 CFU/mL. 2
• Provide intrapartum antibiotic prophylaxis (penicillin, ampicillin, or cefazolin) regardless of colony count, as any GBS bacteriuria indicates colonization status. 1, 2
• Do not re-screen with genital tract or urinary cultures in the third trimester, as these women are presumed to be GBS colonized. 2
• Intrapartum prophylaxis administered ≥4 hours before delivery is 78% effective in preventing early-onset GBS disease. 1

For non-pregnant adults:

• GBS is universally sensitive to beta-lactam antibiotics (penicillin, ampicillin, cephalosporins) but resistant to gentamicin. 4
• Screen for underlying urinary tract abnormalities, as 60% of patients with GBS bacteriuria have structural abnormalities. 4
• Clinical manifestations affect upper and lower urinary tract equally (37% and 38% respectively). 4

Common Pitfalls to Avoid

• Do not dismiss GBS as a contaminant when isolated in urine culture, particularly at counts of 25,000-50,000 CFU/mL. 4, 5
• Do not fail to provide intrapartum prophylaxis in pregnant women with any level of GBS bacteriuria, as this is a critical intervention for preventing neonatal disease. 1, 2
• Do not use aminoglycosides (gentamicin) for GBS treatment, as all isolates show resistance. 4
• Do not overlook the need for urologic evaluation in non-pregnant adults, as the majority have underlying urinary tract abnormalities requiring investigation. 4