Does a positive urine culture with Group B Streptococcus (GBS) require antibiotic treatment?

Management of Group B Streptococcus in Urine Culture

Women with Group B Streptococcus (GBS) bacteriuria in any concentration during pregnancy should receive appropriate treatment at the time of diagnosis as well as intrapartum antibiotic prophylaxis for prevention of early-onset neonatal GBS disease. 1

Understanding GBS Bacteriuria in Pregnancy

GBS bacteriuria is an important clinical finding during pregnancy for several reasons:

• It serves as a marker for heavy genital tract colonization 1
• It increases the risk of delivering an infant with early-onset GBS disease 1
• It can cause both symptomatic and asymptomatic urinary tract infections 1

Significance of Colony Count

The CDC guidelines have evolved regarding the significance of GBS colony counts in urine:

• In 2002, CDC guidelines recommended reporting GBS in urine at any concentration (e.g., 10³ CFU/mL) 1
• The 2010 revised CDC guidelines specify that laboratories should report GBS in urine when present at concentrations of ≥10⁴ CFU/mL in pure culture or mixed with a second microorganism 1

Management Algorithm for GBS Bacteriuria

1. Acute Management of GBS Bacteriuria

• Symptomatic GBS UTI: Treat according to current standards of care for urinary tract infection during pregnancy 1

  • Appropriate antibiotics include nitrofurantoin, first-generation cephalosporins, or other pregnancy-safe antibiotics based on susceptibility testing
  • Avoid ampicillin due to high resistance rates (81.6% in some populations) 2

• Asymptomatic GBS bacteriuria ≥10⁴ CFU/mL: Treat with appropriate antibiotics 1, 3

• Asymptomatic GBS bacteriuria <10⁴ CFU/mL: The 2012 JOGC guideline recommends against treating with antibiotics solely for prevention of adverse outcomes such as pyelonephritis, chorioamnionitis, or preterm birth 3

2. Intrapartum Management

• All women with documented GBS bacteriuria during pregnancy (regardless of colony count) should receive intrapartum antibiotic prophylaxis during labor or when membranes rupture 1, 3
• No repeat screening with vaginal/rectal cultures at 35-37 weeks is necessary for these women 1, 3

3. Antibiotic Recommendations for Intrapartum Prophylaxis

• First-line: Penicillin G, 5 million units IV initial dose, then 2.5 million units IV every 4 hours until delivery 1
• Alternative: Ampicillin, 2 g IV initial dose, then 1 g IV every 4 hours until delivery 1
• For penicillin-allergic women without history of anaphylaxis: Cefazolin, 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1
• For penicillin-allergic women with high risk for anaphylaxis:
  • If GBS is susceptible: Clindamycin, 900 mg IV every 8 hours until delivery OR erythromycin, 500 mg IV every 6 hours until delivery
  • If susceptibility unknown or resistant: Vancomycin, 1 g IV every 12 hours until delivery 1

Important Clinical Considerations

Pitfalls to Avoid

1. Failure to identify GBS bacteriuria: Ensure urine specimens from pregnant women are clearly labeled to assist laboratory processing 1

2. Unnecessary repeat screening: Women with GBS bacteriuria should not be re-screened by genital tract culture or urinary culture in the third trimester, as they are presumed to be GBS colonized 3

3. Inappropriate antibiotic use: In the absence of GBS urinary tract infection, antimicrobial agents should not be used before the intrapartum period to treat asymptomatic GBS colonization, as such treatment is not effective in eliminating carriage or preventing neonatal disease 1

4. Antibiotic resistance concerns: Recent studies show increasing resistance to antibiotics among GBS isolates, with one study reporting 18.3% resistance to penicillin, 81.6% to ampicillin, 23.3% to clindamycin, and 30% to vancomycin 2

Special Circumstances

• Planned cesarean delivery: Women with planned cesarean delivery before labor onset and with intact membranes are at low risk for having an infant with early-onset GBS disease and do not routinely require intrapartum prophylaxis 1

• Threatened preterm delivery: Management is challenging as GBS screening is typically done at 35-37 weeks. If GBS status is unknown and there is substantial risk for preterm delivery, intrapartum antibiotic prophylaxis should be provided pending culture results 1

By following these evidence-based recommendations, clinicians can effectively manage GBS bacteriuria in pregnancy to reduce the risk of adverse maternal and neonatal outcomes, particularly early-onset neonatal GBS disease.