What is the recommended treatment for Group B Streptococcus (GBS) in urine during the third trimester of pregnancy?

Treatment of GBS in Urine During Third Trimester

Women with Group B Streptococcus detected in urine during the third trimester should receive immediate antibiotic treatment for the urinary tract infection according to standard pregnancy UTI protocols, followed by mandatory intrapartum antibiotic prophylaxis during labor, regardless of subsequent culture results or colony count. 1, 2

Immediate Management of GBS Bacteriuria

Treat the UTI promptly using pregnancy-safe antibiotics, regardless of whether symptoms are present. 1, 2 The key principle is that GBS bacteriuria at any concentration is a marker for heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease. 3

Critical Understanding

• GBS bacteriuria indicates heavy colonization of the genital tract, not just a simple urinary infection. 3
• All GBS isolates in urine should be treated regardless of colony count—even low counts (<10⁴ CFU/mL) warrant treatment. 1, 2
• Attempting to eradicate GBS colonization with antibiotics before labor is ineffective; recolonization after treatment is typical. 3, 1

Intrapartum Antibiotic Prophylaxis (The Critical Component)

All women with GBS bacteriuria at any point during the current pregnancy must receive intrapartum antibiotic prophylaxis during labor. 1, 2 This is the intervention that actually prevents neonatal disease, not the prenatal treatment of the UTI.

For Women WITHOUT Penicillin Allergy

First-line regimen:

• Penicillin G: 5 million units IV initial dose, then 2.5-3 million units IV every 4 hours until delivery 2, 4
• Alternative: Ampicillin 2 g IV initial dose, then 1 g IV every 4 hours until delivery 2

The 4-hour dosing interval is critical—more frequent dosing does not increase efficacy, and longer intervals may allow inadequate coverage. 4

For Women WITH Penicillin Allergy

If NOT at high risk for anaphylaxis:

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

If at high risk for anaphylaxis:

• Perform susceptibility testing on the GBS isolate for clindamycin and erythromycin 2
• If susceptible to clindamycin: Clindamycin 900 mg IV every 8 hours until delivery 2
• If resistant or susceptibility unknown: Consult infectious disease specialist 2

Important Management Points

No Need for Repeat GBS Screening

Women with documented GBS bacteriuria during the current pregnancy do not need the routine 35-37 week vaginal-rectal GBS screening. 1, 2 They are already designated for intrapartum prophylaxis regardless of later screening results.

Timing and Effectiveness

Intrapartum antibiotic prophylaxis is highly effective when administered correctly:

• 91% effective in preventing early-onset GBS disease in term infants 5
• 86% effective in preterm infants 5
• Requires at least 4 hours of antibiotic administration before delivery for optimal effectiveness 3, 5

Exception: Planned Cesarean Delivery

Women undergoing planned cesarean delivery before onset of labor and with intact amniotic membranes do not require intrapartum prophylaxis, regardless of GBS status. 3, 2 The risk of early-onset GBS disease in this scenario is extremely low.

Common Pitfalls to Avoid

Do not skip intrapartum prophylaxis even if:

• The prenatal UTI was treated successfully 1, 2
• Subsequent cultures are negative 1
• The woman is asymptomatic at the time of labor 2

Do not rely on prenatal antibiotic treatment alone. Antibiotics given before labor do not eliminate GBS from the genitourinary and gastrointestinal tracts; recolonization is typical. 3, 2 The intrapartum prophylaxis is what prevents neonatal disease by reducing bacterial load during delivery.

Ensure proper antibiotic selection in penicillin-allergic patients. The risk of anaphylaxis (approximately 5 per 10,000 treatments) must be balanced against neonatal risk. 6 Detailed allergy history is essential to guide appropriate alternative therapy.

Clinical Impact

Since implementation of universal screening and intrapartum prophylaxis protocols, early-onset GBS disease has decreased 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 by 2010. 5 This represents over 70,000 prevented cases of invasive neonatal GBS disease. 5