What is the recommended treatment for a patient with a colony count of Beta-hemolytic Group B Streptococcus (GBS) greater than 100,000 Colony-Forming Units per milliliter (CFU/mL)?

Treatment of GBS Bacteriuria >100,000 CFU/mL in Pregnancy

For a pregnant patient with GBS bacteriuria >100,000 CFU/mL, treat the acute urinary tract infection immediately with appropriate antibiotics AND provide intrapartum antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier in pregnancy. 1

Immediate Treatment of the Acute UTI

First-line antibiotic options:

• Penicillin G is the preferred agent due to its narrow spectrum and universal GBS susceptibility 1, 2
• Ampicillin is an acceptable alternative, though it has broader spectrum activity 1, 2
• Treatment should follow standard pregnancy UTI protocols with pregnancy-safe antibiotics based on susceptibility testing 1

For penicillin-allergic patients:

• Cefazolin (2 g IV initial dose, then 1 g IV every 8 hours) for patients NOT at high risk for anaphylaxis 1, 3
• Clindamycin (900 mg IV every 8 hours) if the isolate is confirmed susceptible, for patients at high risk for anaphylaxis 1, 3
• Vancomycin (1 g IV every 12 hours) if susceptibility testing is unavailable or the isolate is resistant to clindamycin 1, 3

Critical Clinical Context: Why Both Treatments Are Required

GBS bacteriuria at ANY concentration during pregnancy is a marker for heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease. 1, 2 The colony count of >100,000 CFU/mL confirms significant bacteriuria requiring immediate attention.

Treating the UTI alone does NOT eliminate GBS colonization from the genitourinary tract—recolonization after oral antibiotics is typical. 1, 2 This is why intrapartum IV prophylaxis remains mandatory even if bacteriuria was treated earlier in pregnancy.

Mandatory Intrapartum Antibiotic Prophylaxis During Labor

All pregnant women with GBS bacteriuria at any point during the current pregnancy MUST receive intrapartum antibiotic prophylaxis during labor, regardless of when or if the UTI was treated. 1, 2

Recommended intrapartum regimen:

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

For penicillin-allergic patients during labor:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until delivery (for non-severe allergy) 1, 3
• Clindamycin: 900 mg IV every 8 hours until delivery (if susceptible, for severe allergy) 1, 3
• Vancomycin: 1 g IV every 12 hours until delivery (if resistance or unknown susceptibility) 1, 3

Timing and Efficacy

Intrapartum prophylaxis administered ≥4 hours before delivery is 78% effective in preventing early-onset neonatal GBS disease. 1, 2 However, even 2 hours of antibiotic exposure has been shown to reduce GBS vaginal colony counts and decrease clinical neonatal sepsis. 5

Obstetric interventions should NOT be delayed solely to achieve 4 hours of antibiotic administration before delivery. 4, 5

Common Pitfalls to Avoid

• Do NOT assume that treating the UTI eliminates the need for intrapartum prophylaxis—this is the most critical error, as recolonization is typical and the risk of neonatal disease persists 1, 2
• Do NOT use oral antibiotics alone for GBS prophylaxis—they are inadequate and ineffective 4, 2
• Do NOT treat asymptomatic GBS colonization before labor—antimicrobial agents should not be used before the intrapartum period as this does not eliminate carriage and may promote resistance 1, 2
• Ensure laboratories are informed the specimen is from a pregnant woman so they report GBS at concentrations ≥10,000 CFU/mL 1
• Verify penicillin allergy history carefully, as many reported allergies are not true IgE-mediated reactions, and patients may be candidates for penicillin rather than alternatives 1, 3

Susceptibility Testing Requirements

For penicillin-allergic patients at high risk for anaphylaxis, susceptibility testing for clindamycin and erythromycin MUST be performed on the GBS isolate. 4, 1, 2 Testing for inducible clindamycin resistance is necessary for isolates susceptible to clindamycin but resistant to erythromycin. 1