What is the recommended treatment for Streptococcus agalactiae (Group B Streptococcus, GBS) infections?

Treatment of Streptococcus agalactiae (Group B Streptococcus) Infections

Penicillin G is the first-line treatment for Streptococcus agalactiae (Group B Streptococcus, GBS) infections due to its proven efficacy and the absence of clinically significant resistance. 1, 2

First-Line Treatment Options

For Invasive GBS Infections:

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours 1
• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours 1

For GBS Urinary Tract Infections:

• Treatment should follow standard UTI protocols with penicillin or ampicillin as first-line agents
• Continue treatment for 5-7 days for uncomplicated UTIs and 10-14 days for complicated UTIs 1

Alternative Treatment Options for Penicillin-Allergic Patients

For Patients with Non-Anaphylactic Penicillin Allergy:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 3, 1

For Patients with High Risk of Anaphylaxis:

• Clindamycin: 900 mg IV every 8 hours (if isolate is confirmed susceptible) 3, 1
• Vancomycin: 1 g IV every 12 hours (if susceptibility results unavailable or resistance to clindamycin) 3, 1

Antimicrobial Resistance Considerations

• GBS remains universally susceptible to penicillin and ampicillin 2, 4
• Increasing resistance to macrolides and clindamycin has been observed:
  • Erythromycin resistance rates: 4.7-30% 4, 5
  • Clindamycin resistance rates: 7-28% 4, 5
• Susceptibility testing is essential when using alternatives to penicillin 3, 5
• The macrolide-lincosamide-streptogramin B (MLSB) phenomenon occurs in approximately 4% of isolates, causing inducible clindamycin resistance 2

Intrapartum Antibiotic Prophylaxis for GBS

Intrapartum antibiotic prophylaxis is indicated for:

• Women with positive GBS vaginal/rectal culture at 35-37 weeks gestation
• Women with GBS bacteriuria during the current pregnancy
• Women with previous infant with invasive GBS disease
• Women with unknown GBS status who deliver at <37 weeks, have rupture of membranes ≥18 hours, or develop intrapartum fever ≥38°C 1

Prophylaxis Regimens:

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

Treatment of Neonatal GBS Disease

For neonates with suspected or confirmed GBS disease:

• Full diagnostic evaluation including blood culture, CBC with differential, and lumbar puncture if stable
• Initiate antibiotic therapy directed at GBS and other common pathogens (including E. coli)
• Continue antibiotics for at least 48-72 hours after symptoms resolve 3

Important Clinical Considerations

1. Penicillin preference: Penicillin G is preferred over ampicillin for routine prophylaxis due to its narrower spectrum, which may reduce selection of resistant organisms 3

2. Susceptibility testing: For penicillin-allergic patients, susceptibility testing of GBS isolates to clindamycin and erythromycin is essential due to increasing resistance 3, 5

3. Inducible resistance: If a GBS isolate is resistant to erythromycin but susceptible to clindamycin, testing for inducible clindamycin resistance should be performed 3

4. Treatment duration: Continue treatment until clinical improvement and for at least 48-72 hours after symptoms resolve 1

5. Vaccine development: A pentavalent GBS vaccine currently in trials may provide coverage for up to 97% of isolates, potentially reducing the need for antibiotic prophylaxis in the future 2, 6