Should a pregnant woman with a positive rectovaginal Group B Streptococcus culture at 35‑37 weeks receive intrapartum antibiotic prophylaxis, and should asymptomatic non‑pregnant adults colonized with GBS be treated?

Management of Group B Streptococcus Colonization

Pregnant women with positive rectovaginal GBS cultures at 35–37 weeks must receive intravenous intrapartum antibiotic prophylaxis during labor, but asymptomatic non-pregnant adults colonized with GBS should never be treated.

Pregnant Women: Universal Screening and Intrapartum Prophylaxis

Screening Protocol

• All pregnant women should undergo vaginal-rectal GBS screening between 36 0/7 and 37 6/7 weeks of gestation using a single swab collected first from the lower vagina then inserted through the anal sphincter into the rectum. 1, 2, 3
• The specimen must be placed in non-nutritive transport medium and incubated 1–4 hours at 35–37°C in enrichment broth to maximize GBS recovery. 1, 2
• A negative GBS screen remains valid for only 5 weeks; beyond this window, rescreening is required. 1, 2

When Intrapartum Prophylaxis Is Mandatory

• Positive vaginal-rectal GBS culture at 36 0/7–37 6/7 weeks requires IV antibiotics during labor. 1, 2, 3
• Any concentration of GBS bacteriuria during any trimester of the current pregnancy mandates both immediate UTI treatment and intrapartum prophylaxis during labor, regardless of whether the UTI was treated earlier. 1, 4
• Previous infant with invasive GBS disease automatically qualifies the mother for prophylaxis in subsequent pregnancies. 1, 2
• Unknown GBS status at labor onset with any of the following: delivery <37 weeks, membrane rupture ≥18 hours, or intrapartum temperature ≥38.0°C. 1, 2

Antibiotic Regimens for Intrapartum Prophylaxis

For women without penicillin allergy:

• Penicillin G 5 million units IV initially, then 2.5–3.0 million units IV every 4 hours until delivery is the preferred agent due to narrow spectrum and universal GBS susceptibility. 1, 3, 5
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery is an acceptable alternative when penicillin G is unavailable. 1, 3

For women with low-risk penicillin allergy (no anaphylaxis, angioedema, respiratory distress, or urticaria):

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery is the preferred alternative. 1, 3, 5

For women with high-risk penicillin allergy:

• Susceptibility testing for clindamycin and erythromycin must be performed on the antenatal GBS isolate. 1, 2, 5
• If susceptible to both agents: Clindamycin 900 mg IV every 8 hours until delivery. 1, 3
• If resistant to either agent or susceptibility unknown: Vancomycin 1 g IV every 12 hours until delivery. 1, 3
• D-zone testing is required for isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible resistance. 1, 2

Timing and Effectiveness

• Administering antibiotics ≥4 hours before delivery reduces early-onset neonatal GBS disease by 78–89%, though prophylaxis should begin as soon as labor starts and not be delayed to reach this interval. 1, 3, 5
• Even 2 hours of antibiotic exposure reduces GBS vaginal colony counts and decreases clinical neonatal sepsis diagnoses. 3
• Obstetric interventions should never be delayed solely to provide 4 hours of antibiotic administration. 3, 5

Critical Pitfall: Never Treat Asymptomatic Colonization Before Labor

Oral or IV antibiotics given before the intrapartum period are completely ineffective at eliminating GBS colonization and should never be used for asymptomatic vaginal colonization. 1, 2, 4

• Treating GBS colonization before labor does not prevent neonatal disease, promotes antibiotic resistance, and causes unnecessary adverse drug effects. 1, 2
• Recolonization after oral antibiotics is typical, which is why intrapartum IV prophylaxis remains mandatory even if bacteriuria was treated earlier in pregnancy. 1

Non-Pregnant Adults: Do Not Treat Asymptomatic Colonization

Asymptomatic GBS bacteriuria in non-pregnant adults should never be treated, regardless of colony count. 1

Evidence Against Treatment

• The 2019 Infectious Diseases Society of America (IDSA) guidelines provide a strong recommendation against treating asymptomatic bacteriuria in non-pregnant populations, stating it leads to unnecessary antibiotic exposure, resistance development, and adverse drug effects without clinical benefit. 1
• Treating asymptomatic bacteriuria in hospitalized patients with delirium did not improve outcomes and was associated with higher rates of Clostridioides difficile infection and worse functional recovery. 1

Specific Non-Pregnant Populations Who Should NOT Be Treated

• Adults with diabetes mellitus. 1
• Elderly or institutionalized individuals. 1
• Patients with indwelling urinary catheters (short-term or long-term). 1
• Individuals with neurogenic bladder on intermittent catheterization. 1
• Patients undergoing non-urologic surgery (including orthopedic/arthroplasty). 1
• Patients with a history of recurrent UTIs. 1

Only Exception for Non-Pregnant Adults

• Treatment is indicated only when the patient is scheduled for an endoscopic urologic procedure involving mucosal trauma. 1
• Antibiotic therapy is also appropriate when classic urinary symptoms (dysuria, frequency, urgency, suprapubic pain, flank tenderness) or systemic signs of infection (fever, rigors, hemodynamic instability) are present. 1

Special Pregnancy Scenarios

Preterm Labor (<37 Weeks)

• Women presenting with signs of preterm labor and unknown GBS status should receive IV prophylaxis immediately at hospital admission without awaiting culture results. 1, 2
• Prophylaxis should be discontinued if the patient is not in true labor or if a GBS culture becomes available and is negative. 1, 2

Preterm Premature Rupture of Membranes (PPROM)

• Ampicillin 2 g IV once, followed by 1 g IV every 6 hours for at least 48 hours, is adequate for both latency prolongation and GBS prophylaxis. 1
• Patients with GBS-positive status and PPROM after 34 weeks are not candidates for expectant management due to higher rates of neonatal infectious complications. 6

GBS Bacteriuria in Pregnancy

• Any concentration of GBS in urine during pregnancy—including counts as low as 10,000 CFU/mL—requires immediate treatment of the UTI and mandatory intrapartum prophylaxis during labor. 1, 4
• GBS bacteriuria is a marker for heavy genital tract colonization and significantly increases the risk of early-onset neonatal disease. 1, 4
• Women with documented GBS bacteriuria at any point in pregnancy should not be re-screened with vaginal-rectal cultures in the third trimester, as they are presumed to be GBS colonized. 1