What is the recommended treatment for Streptococcus agalactiae infections?

Treatment of Streptococcus agalactiae (Group B Streptococcus) Infections

Penicillin or ampicillin remain the first-line antibiotics for all Streptococcus agalactiae infections, as universal susceptibility to beta-lactams has been consistently demonstrated and no penicillin resistance has ever been documented. 1, 2, 3, 4

Treatment by Clinical Syndrome

Neonatal Infections (Early and Late Onset Disease)

• Combination therapy with penicillin G (or ampicillin) plus gentamicin is the standard treatment for neonatal GBS sepsis and meningitis 5, 3
• Penicillin G dosing for neonates: 200,000 to 300,000 units/kg/day (administered as 50,000 units/kg every 4 to 6 hours) for 10 to 14 days 1
• For meningitis specifically: 250,000 units/kg/day in equal doses every 4 hours for 10 to 14 days 1
• For endocarditis: 250,000 units/kg/day in equal doses every 4 hours for 4 weeks 1
• Gentamicin is added for synergy, particularly important in severe infections 3

Adult Infections

Soft Tissue Infections and Cellulitis

• For nonpurulent cellulitis, empirical therapy targeting beta-hemolytic streptococci (including GBS) with beta-lactam antibiotics is recommended 6
• Penicillin G: 12 to 20 million units/day in divided doses for serious infections 1
• Alternative oral options: cephalexin 500 mg every 6 hours or cefazolin 0.5-1 g every 8 hours IV 6
• Duration: 5-10 days based on clinical response 6

Endocarditis

• For highly penicillin-susceptible streptococcal endocarditis (including GBS), a 4-week regimen of intravenous aqueous crystalline penicillin G achieves high cure rates 6
• Adult dosing: 12 to 20 million units/day for 4 to 6 weeks 1
• Ceftriaxone once daily is an acceptable alternative for the full 4-week course 6
• For prosthetic valve endocarditis: extend therapy to 6 weeks with penicillin, ampicillin, or ceftriaxone combined with gentamicin for the first 2 weeks 6

Urinary Tract Infections

• Ampicillin demonstrates high in vitro sensitivity (>95%) for GBS urinary infections 7
• Augmentin (amoxicillin-clavulanate), cephalothin, or rifampicin are alternatives with 100% susceptibility to rifampicin documented 7
• Identify and treat reservoirs (vagina, urethra, gastrointestinal tract) to prevent recurrence 7

Penicillin Allergy Management

Mild Allergic Reactions

• Cefazolin is the preferred alternative for patients with non-severe penicillin allergy 6
• Cephalexin 500 mg every 6 hours orally is an option for outpatient management 6

Severe Allergic Reactions (Anaphylaxis)

• Vancomycin 15 mg/kg every 12 hours IV is the recommended alternative 6
• Clindamycin is NOT reliably effective due to significant resistance rates 6, 2

Critical Resistance Patterns

Macrolide and Lincosamide Resistance

• Erythromycin resistance ranges from 12-32% and clindamycin resistance from 7-44% in recent surveillance data 6, 2, 4
• Resistance has increased significantly over time: erythromycin resistance rose from 4.7% (1993-1997) to 12% (1999) in German surveillance 3
• Do NOT use clindamycin or erythromycin empirically without susceptibility testing 6, 2

Universal Beta-Lactam Susceptibility

• All GBS isolates remain 100% susceptible to penicillin, ampicillin, and cefotaxime 2, 3, 4
• This universal susceptibility has been maintained across all geographic regions and time periods studied 2, 3, 4

Intrapartum Antibiotic Prophylaxis (IAP)

• Penicillin G or ampicillin are first-line agents for IAP to prevent neonatal transmission 2, 5
• For penicillin-allergic pregnant women at low risk of anaphylaxis: cefazolin 2
• For severe penicillin allergy: vancomycin (NOT clindamycin due to resistance) 2
• Antimicrobial susceptibility testing should be performed before IAP given the high macrolide resistance rates 2

Duration of Therapy

• Maintain antibiotic therapy for Group A and Group B beta-hemolytic streptococcal infections for at least 10 days to reduce complications 1
• Endocarditis: 4 weeks for native valve, 6 weeks for prosthetic material 6, 1
• Meningitis: 10-14 days 1
• Soft tissue infections: 5-10 days based on clinical response 6
• Continue treatment for at least 48-72 hours after the patient becomes asymptomatic 1

Common Pitfalls

• Avoid clindamycin or erythromycin without documented susceptibility due to resistance rates exceeding 20-40% in many regions 6, 2, 4
• Do not use rifampin as monotherapy or adjunctive therapy for soft tissue infections 6
• Gentamicin must be included in susceptibility testing when treating chorioamnionitis, as it is used synergistically with penicillin 2
• For urinary tract infections, identify extraurinary reservoirs to prevent treatment failure 7