What is the recommended treatment for a pregnant woman with a Strep (Streptococcus) agalactiae urinary tract infection (UTI)?

Treatment of Group B Streptococcus (Strep agalactiae) UTI in Pregnant Women

Pregnant women with GBS bacteriuria at any concentration must receive immediate treatment of the acute UTI followed by mandatory intravenous antibiotic prophylaxis during labor, regardless of when the UTI was treated. 1

Immediate Treatment of Acute UTI

First-Line Antibiotic Options

• Ampicillin 500 mg orally every 8 hours for 7-10 days is the preferred oral agent for treating the acute infection in pregnancy 1, 2
• Amoxicillin 500 mg orally every 6-8 hours for 7-10 days is an acceptable alternative 2
• For severe presentations or inability to tolerate oral therapy, ampicillin 2 g IV every 4-6 hours can be used initially, then transition to oral therapy once stable 1

Penicillin-Allergic Patients

• Cefazolin 2 g IV initially, then 1 g IV every 8 hours for patients not at high risk for anaphylaxis 1
• Clindamycin 300-450 mg orally every 8 hours (or 900 mg IV every 8 hours) if the isolate is confirmed susceptible, for patients at high risk for anaphylaxis 1
• Vancomycin 1 g IV every 12 hours if clindamycin susceptibility is unknown or the isolate is resistant 1
• Susceptibility testing must be performed for penicillin-allergic patients at high risk for anaphylaxis, including testing for inducible clindamycin resistance 1

Critical Understanding: Why Intrapartum Prophylaxis is Mandatory

Treating the UTI during pregnancy does NOT eliminate GBS colonization from the genitourinary tract—recolonization after oral antibiotics is typical. 1 This is why intrapartum IV prophylaxis remains mandatory even if bacteriuria was treated earlier in pregnancy.

Key Clinical Context

• GBS bacteriuria at any concentration is a marker for heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease 1
• Women with GBS bacteriuria are presumed to be heavily colonized and automatically qualify for intrapartum prophylaxis, regardless of colony count 1
• Intrapartum prophylaxis administered ≥4 hours before delivery is 78% effective in preventing early-onset neonatal GBS disease 1

Mandatory Intrapartum Antibiotic Prophylaxis During Labor

First-Line Intrapartum Regimen (No 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
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery is an acceptable alternative 1, 3

Alternative Intrapartum Regimens (Penicillin Allergy)

• For non-high-risk allergy: Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery 1, 3
• For high-risk allergy with susceptible isolate: Clindamycin 900 mg IV every 8 hours until delivery 1, 3
• For high-risk allergy with resistant or unknown susceptibility: Vancomycin 1 g IV every 12 hours until delivery 1, 3

High-risk for anaphylaxis includes history of immediate hypersensitivity reactions (anaphylaxis, angioedema, urticaria) or history of asthma that would make anaphylaxis more dangerous 1

Special Pregnancy Scenarios

Preterm Labor (<37 weeks)

• Women admitted with signs and symptoms of preterm labor with GBS bacteriuria should receive GBS prophylaxis immediately at hospital admission 1

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 and GBS prophylaxis 1

Planned Cesarean Delivery

• Women undergoing planned cesarean delivery before labor onset with intact membranes do not routinely require intrapartum prophylaxis 1, 3

Critical Pitfalls to Avoid

Common Dangerous Errors

• Never assume that treating the UTI eliminates the need for intrapartum prophylaxis—this is a common and dangerous error that significantly increases neonatal risk 1
• Never use oral antibiotics before labor to "treat" GBS colonization—this is completely ineffective at eliminating colonization and promotes antibiotic resistance 1, 3
• Women with GBS bacteriuria should not be re-screened with vaginal-rectal cultures at 35-37 weeks, as they are presumed colonized 1

Documentation Requirements

• Ensure laboratory reports of GBS bacteriuria are communicated to both the anticipated site of delivery and the ordering provider 1
• Laboratories should report GBS present at ≥10,000 CFU/mL (≥10⁴ CFU/mL) as the threshold for clinical significance in pregnancy 1

Antibiotic Resistance Patterns

• All GBS strains remain fully sensitive to penicillin, ampicillin, and vancomycin 4
• High resistance exists for clindamycin (77%) and tetracycline (88%), making susceptibility testing essential before using clindamycin 4
• Resistance to clindamycin ranges from 3-15% in various populations, reinforcing the need for testing 1