Do we treat Group B Streptococcus (GBS) bacteriuria with colony counts of 10,000 to 49,000 Colony-Forming Units per Milliliter (CFU/mL)?

Treatment of GBS Bacteriuria with Colony Counts 10,000-49,000 CFU/mL

Treatment depends entirely on pregnancy status: pregnant women with ANY concentration of GBS in urine require both immediate treatment of the UTI and intrapartum antibiotic prophylaxis during labor, while non-pregnant patients should only be treated if symptomatic or have urinary tract abnormalities. 1, 2

For Pregnant Women

All pregnant women with GBS bacteriuria at any concentration—including 10,000-49,000 CFU/mL—must receive treatment at diagnosis followed by intrapartum prophylaxis during labor, regardless of symptoms. 3, 1, 4

Rationale for Treatment in Pregnancy

• GBS bacteriuria during pregnancy is a marker for heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease 3, 1
• The CDC guidelines specify that laboratories should report GBS present at ≥10^4 CFU/mL (10,000 CFU/mL), establishing this as the threshold for clinical significance in pregnancy 3, 1
• Treatment of the acute UTI does NOT eliminate GBS colonization from the genitourinary tract, and recolonization after antibiotics is typical—this is why intrapartum prophylaxis is still required even after treating the UTI 1

Treatment Protocol for Pregnant Women

Immediate UTI Treatment Options:

• Amoxicillin 500 mg orally three times daily for 3-7 days 2
• Cephalexin 500 mg orally four times daily for 3-7 days 2
• Nitrofurantoin 100 mg orally twice daily for 5-7 days (avoid in late pregnancy) 2

Mandatory Intrapartum Prophylaxis During Labor:

• Penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery (preferred agent) 1, 2
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative) 1
• For penicillin-allergic patients not at high risk for anaphylaxis: Cefazolin 2 g IV initially, then 1 g IV every 8 hours 1, 2
• For high-risk penicillin allergy: Clindamycin 900 mg IV every 8 hours (if susceptible) or vancomycin 1 g IV every 12 hours 1

Critical Points for Pregnancy Management

• No repeat GBS screening at 35-37 weeks is needed for women with documented GBS bacteriuria during pregnancy—they are presumed colonized 2, 4
• Intrapartum prophylaxis reduces early-onset GBS disease by 78% when administered ≥4 hours before delivery 1
• Women undergoing planned cesarean delivery before labor onset and membrane rupture do not require GBS prophylaxis 2

For Non-Pregnant Patients

Non-pregnant patients with GBS bacteriuria at 10,000-49,000 CFU/mL should NOT be treated unless they are symptomatic or have underlying urinary tract abnormalities. 3, 5

Rationale Against Treatment in Non-Pregnant Asymptomatic Patients

• The 2019 IDSA guidelines provide strong evidence against screening for or treating asymptomatic bacteriuria in non-pregnant populations 3, 5
• GBS in urine with colony counts 10,000-49,000 CFU/mL in asymptomatic non-pregnant patients represents asymptomatic bacteriuria that should not be treated 5
• Treating asymptomatic bacteriuria leads to unnecessary antibiotic exposure, resistance development, and potential adverse drug effects without clinical benefit 5

When Treatment IS Indicated in Non-Pregnant Patients

Treat if the patient has:

• Symptomatic UTI (dysuria, frequency, urgency, suprapubic pain) 5
• Fever or systemic symptoms suggesting pyelonephritis 5
• Underlying urinary tract abnormalities (neurogenic bladder, structural abnormalities, immunosuppression) 5

Treatment Options for Symptomatic Non-Pregnant Patients:

• Penicillin G 500 mg orally every 6-8 hours for 7-10 days (preferred) 5
• Ampicillin 500 mg orally every 8 hours for 7-10 days 5
• Clindamycin 300-450 mg orally every 8 hours (for penicillin allergy, with susceptibility testing) 5

Common Pitfalls to Avoid

• Do not apply pregnancy guidelines to non-pregnant patients: The CDC mandate to treat all GBS bacteriuria applies specifically to pregnant women to prevent neonatal disease and should not be extrapolated to non-pregnant individuals 5
• Do not skip intrapartum prophylaxis in pregnancy: Even if the UTI was treated earlier in pregnancy, intrapartum prophylaxis is still mandatory because treatment does not eliminate colonization 1, 4
• Do not treat asymptomatic non-pregnant patients: This represents overtreatment and contributes to antibiotic resistance without clinical benefit 3, 5
• Do not use colony count thresholds to decide on intrapartum prophylaxis in pregnancy: Any concentration of GBS in urine during pregnancy mandates intrapartum prophylaxis 3, 1