Treatment of Group B Streptococcal Infections in Non-Pregnant Adults
For non-pregnant adults with Group B streptococcal (GBS) infections, penicillin G remains the drug of choice, with ampicillin as an acceptable alternative. 1, 2
First-Line Treatment Options
Penicillin G: The preferred first-line agent
- Dosing: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours
- Note: GBS requires higher doses of penicillin compared to Group A streptococci, as minimum inhibitory concentrations are 4-8 fold higher 1
Ampicillin: An acceptable alternative
- Dosing: 2 g IV initial dose, then 1 g IV every 4 hours
For Penicillin-Allergic Patients
Treatment should be guided by antimicrobial susceptibility testing due to increasing resistance patterns:
For patients with non-severe penicillin allergy:
- Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours
For patients with severe penicillin allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):
- If GBS isolate is susceptible to clindamycin:
- Clindamycin: 900 mg IV every 8 hours
- If susceptibility testing is unavailable or isolate is resistant to clindamycin:
- Vancomycin: 1 g IV every 12 hours
- If GBS isolate is susceptible to clindamycin:
Important Considerations
Antimicrobial Resistance
- Resistance to erythromycin and clindamycin is increasing significantly 1
- Clindamycin resistance rates range from 14-26.6% among GBS isolates
- Erythromycin is no longer recommended for GBS infections due to resistance rates of 14.5-32.9%
- Always order susceptibility testing for isolates from penicillin-allergic patients
Clinical Presentations
GBS in non-pregnant adults commonly presents as:
- Skin and soft tissue infections (31.9%)
- Primary bacteremia (34%)
- Urinary tract infections
- Less commonly: pneumonia, meningitis, endocarditis, and osteoarticular infections 1
Risk Factors
Patients at increased risk for invasive GBS disease include:
- Elderly individuals
- Those with diabetes mellitus (42.6% of cases)
- Patients with malignancy (43.6% of cases)
- Liver cirrhosis (16% of cases)
- Neurological impairment 1, 2
Treatment Duration
- Duration of therapy should be determined by the site and severity of infection
- For bacteremia without focus: minimum 10-14 days
- For endocarditis: 4-6 weeks
- For meningitis: 2-3 weeks
- For soft tissue infections: 1-2 weeks after clinical improvement
Combination Therapy Considerations
- The addition of gentamicin to penicillin contributes to faster killing at low penicillin concentrations, but only within the first few hours
- After 24 hours, penicillin alone is bactericidal and synergism is not observed 3
- Combination therapy with gentamicin may be considered for severe infections like endocarditis, but is not routinely required for most GBS infections
Treatment Monitoring
- Monitor clinical response within 48-72 hours
- Follow-up blood cultures in bacteremic patients to ensure clearance
- Be aware that recurrent infection occurs in approximately 4.3% of survivors 1
Remember that GBS infections in non-pregnant adults are increasing, particularly in elderly persons and those with significant underlying diseases, and are associated with substantial mortality in these populations 2.