Do we treat Group B Streptococcus (GBS) colonization with 1000-9000 Colony-Forming Units per Milliliter (CFU/mL) that is hemolytic?

Management of Group B Streptococcus Colonization with 1000-9000 CFU/mL

Patients with Group B Streptococcus (GBS) in the urine should be treated at term with antibiotic prophylaxis, regardless of the colony count of the culture. 1

Understanding GBS Colonization and Risk Assessment

GBS colonization is common, affecting approximately 10-30% of pregnant women in the vagina or rectum 2. The presence of GBS in any amount is clinically significant when detected in:

• Vaginal-rectal screening cultures at 36 0/7 to 37 6/7 weeks of gestation
• Urine cultures during pregnancy, regardless of colony count
• Previous history of a baby with invasive GBS disease

Key Points About GBS Colonization:

• GBS in urine, even at low colony counts (1000-9000 CFU/mL), is considered a surrogate marker for heavy maternal colonization 2
• Beta-hemolytic properties of the organism indicate its virulence potential
• GBS colonization can be transient, intermittent, or persistent during pregnancy 2
• The gastrointestinal tract serves as the primary reservoir for GBS and is likely the source of vaginal colonization 2

Management Recommendations

For Pregnant Women:

1. Do not treat GBS colonization with oral antibiotics during pregnancy

   • Oral antibiotics are ineffective in eliminating carriage or preventing neonatal disease 3
   • Treatment should be reserved for intrapartum prophylaxis

2. Provide intrapartum antibiotic prophylaxis (IAP) at onset of labor or rupture of membranes if:

   • GBS is detected in urine at any concentration during pregnancy 2, 3, 1
   • Positive vaginal-rectal screening culture at 36-37 weeks
   • Previous infant with invasive GBS disease
   • Unknown GBS status with risk factors (preterm delivery, prolonged rupture of membranes, fever)

Recommended Antibiotic Regimens for IAP:

First-line therapy:

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery 3

Alternatives:

• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery
• For penicillin-allergic patients with low risk of anaphylaxis: Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours
• For penicillin-allergic patients with high risk of anaphylaxis: Clindamycin or vancomycin based on susceptibility testing 3

Clinical Considerations and Pitfalls

Important Caveats:

1. Colony count is not relevant for treatment decisions

   • Any detection of GBS in urine during pregnancy warrants IAP at delivery, regardless of concentration 1
   • Beta-hemolytic properties indicate potential virulence

2. Timing of IAP is critical

   • Optimal protection occurs when antibiotics are administered at least 4 hours before delivery 3
   • Even 2 hours of antibiotic exposure has been shown to reduce GBS vaginal colony counts

3. Avoid these common errors:

   • Do not treat with oral antibiotics during pregnancy
   • Do not ignore low colony counts in urine specimens
   • Do not wait for symptoms of infection to appear before providing IAP
   • Do not rely on risk factors alone if GBS status is known to be positive

Special Situations:

• Planned cesarean delivery: IAP not required if no labor and membranes intact, even with positive GBS status
• Preterm labor with unknown GBS status: Provide IAP until culture results available
• GBS bacteriuria: Treat symptomatic UTI during pregnancy AND provide IAP at delivery regardless of subsequent cultures 3

By following these evidence-based guidelines, the risk of early-onset GBS disease in neonates can be significantly reduced, which has been demonstrated by the decrease in incidence since implementation of universal screening and IAP protocols 2, 3.