What is the recommended treatment for pregnant women colonized with Group B Streptococcus (GBS)?

Management of Group B Streptococcus (GBS) Colonization in Pregnancy

All pregnant women colonized with GBS should receive intrapartum antibiotic prophylaxis during labor, not antepartum treatment, as prenatal antibiotics are ineffective at preventing neonatal disease and may cause harm. 1, 2

Universal Screening Strategy

• Screen all pregnant women at 35-37 weeks' gestation with both vaginal and rectal swabs to identify GBS colonization 1, 2
• Collect specimens by swabbing the lower vagina (vaginal introitus) first, then inserting the swab through the anal sphincter into the rectum 1
• Place swabs in non-nutritive transport medium (Amies or Stuart's without charcoal) and label clearly for GBS culture 2
• Do not use a speculum or collect cervical cultures, as these reduce detection sensitivity 1

Who Receives Intrapartum Antibiotic Prophylaxis

Prophylaxis is indicated for:

• Women with positive GBS screening culture at 35-37 weeks in the current pregnancy 1, 2
• Women with GBS bacteriuria at any concentration during the current pregnancy (no additional screening needed) 1, 2
• Women who previously delivered an infant with invasive GBS disease (no screening needed) 1, 2
• Women with unknown GBS status at labor onset who have any of these risk factors: gestational age <37 weeks, membrane rupture ≥18 hours, or temperature ≥100.4°F (≥38.0°C) 1, 2

Prophylaxis is NOT indicated for:

• Women with negative vaginal-rectal GBS screening at 35-37 weeks, regardless of risk factors 1
• Women undergoing planned cesarean delivery before labor onset with intact membranes, regardless of GBS status 1
• Women with GBS colonization in a previous pregnancy (unless current pregnancy has an indication) 1

Intrapartum Antibiotic Regimens

For women without penicillin allergy:

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery (preferred agent) 1, 2, 3
• Ampicillin: 2g IV initial dose, then 1g IV every 4 hours until delivery (acceptable alternative) 1, 2, 3

For women with penicillin allergy NOT at high risk for anaphylaxis:

• Cefazolin: 2g IV initial dose, then 1g IV every 8 hours until delivery 3

For women at high risk for anaphylaxis (history of anaphylaxis, angioedema, urticaria, or respiratory distress with penicillin):

• Clindamycin: 900 mg IV every 8 hours until delivery (only if GBS isolate confirmed susceptible) 1, 3
• Vancomycin: 1g IV every 12 hours until delivery (if susceptibility unknown or isolate resistant to clindamycin) 1, 3
• Susceptibility testing for clindamycin and erythromycin must be performed on prenatal GBS isolates from these women 3

Critical Timing Considerations

• Optimal prophylaxis requires at least 4 hours of antibiotic administration before delivery to achieve adequate fetal drug levels 1, 4
• IAP effectiveness is 91% for term infants and 86% for preterm infants when first-line therapy is given for ≥4 hours 4
• Do not delay medically necessary obstetric procedures to achieve 4 hours of prophylaxis 1

Special Clinical Situations

Threatened preterm labor:

• Obtain vaginal-rectal swab for GBS culture and start GBS prophylaxis immediately 2
• If determined not to be in true labor, discontinue prophylaxis 2

Preterm premature rupture of membranes (pPROM):

• Obtain GBS culture and start antibiotics for latency 2, 5
• Ampicillin 2g IV once, followed by 1g IV every 6 hours for at least 48 hours is adequate for both latency and GBS prophylaxis 2, 5
• If GBS culture returns negative, no additional GBS prophylaxis needed at labor onset (negative screen valid for 5 weeks) 5

GBS urinary tract infection:

• Treat the UTI according to standard protocols during pregnancy 1, 2, 3
• These women must still receive intrapartum antibiotic prophylaxis during labor regardless of prior treatment 2, 3
• No additional GBS screening at 35-37 weeks is needed 2, 3

Common Pitfalls to Avoid

• Never use antibiotics before the intrapartum period to eradicate GBS colonization—this is ineffective at eliminating carriage, does not prevent neonatal disease, and may promote antibiotic resistance 1, 2, 3
• Do not withhold intrapartum prophylaxis for women with GBS bacteriuria in the current pregnancy, even if subsequent cultures are negative 3
• Erythromycin is no longer acceptable for intrapartum prophylaxis in penicillin-allergic women 1
• Do not use amoxicillin/clavulanic acid for pPROM due to increased risk of neonatal necrotizing enterocolitis 5
• Oral antibiotics alone are inadequate for GBS prophylaxis 5

Impact of Universal Screening Strategy

• Universal screening and IAP have reduced early-onset GBS disease incidence by more than 80% in the United States, from 1.8 cases per 1,000 live births in the early 1990s to 0.26 cases per 1,000 live births in 2010 4
• An estimated 70,000 cases of early-onset GBS disease were prevented between 1994 and 2010 4
• However, late-onset disease (after 7 days of life) has not been impacted by IAP 4