Management of Streptococcus agalactiae (Group B Streptococcus) Bacteremia in Older Men
For an older man with Streptococcus agalactiae bacteremia, initiate high-dose intravenous penicillin G (12–24 million units/day divided every 4–6 hours) combined with gentamicin for the first 2 weeks, then continue penicillin alone for a total of 4 weeks if endocarditis is present, or 2–4 weeks for other invasive infections. 1, 2
Initial Antibiotic Regimen
Penicillin G remains the drug of choice for Group B Streptococcus bacteremia because all GBS isolates remain universally susceptible to penicillin, with no documented resistance worldwide. 3, 4, 5
High-dose penicillin G (12–20 million units/day IV divided every 4–6 hours) is required because GBS has somewhat higher minimal inhibitory concentrations than Group A Streptococcus, necessitating higher doses for adequate bactericidal activity. 1, 5
Add gentamicin for synergy during the first 2 weeks of treatment for serious invasive infections including bacteremia, sepsis, and endocarditis, as the combination enhances effectiveness against GBS. 1, 6
Ampicillin (2 g IV every 4–6 hours) is an acceptable alternative to penicillin G and is FDA-approved for GBS septicemia and endocarditis, with equivalent efficacy. 6
Treatment Duration Based on Clinical Presentation
For endocarditis caused by GBS, treat for 4 weeks minimum with penicillin or ampicillin; gentamicin should be given for the first 2 weeks only. 1
For primary bacteremia without endocarditis, treat for 2–4 weeks depending on clinical response and presence of metastatic foci. 1, 4
For skin and soft tissue infections with bacteremia, treat for 2–3 weeks after source control and clinical improvement. 5
For osteomyelitis or septic arthritis with bacteremia, treat for 4–6 weeks with consideration for surgical debridement. 5, 7
Mandatory Diagnostic Evaluation
Obtain echocardiography (preferably transesophageal) in all cases of GBS bacteremia to rule out endocarditis, as this complication occurs in 2–10% of cases and dramatically alters treatment duration. 1, 3
Assess for metastatic foci including bone/joint infections, meningitis, and deep abscesses, as GBS can cause suppurative complications requiring surgical intervention. 5, 7
Identify the portal of entry by examining skin/soft tissues (most common source at 24%), urinary tract, respiratory tract, and intravenous access sites. 3, 8, 7
Management of Penicillin Allergy
For non-anaphylactic penicillin allergy, use cefazolin 2 g IV every 8 hours as a first-generation cephalosporin with excellent GBS coverage and only 0.1% cross-reactivity risk. 9, 2
For immediate/anaphylactic penicillin allergy, use vancomycin 15 mg/kg IV every 12 hours plus clindamycin 600–900 mg IV every 8 hours as all GBS isolates remain susceptible to vancomycin. 1, 2
Avoid macrolides (erythromycin, azithromycin) for empiric treatment because erythromycin resistance increased from 8% to 18% during the 1990s and continues to rise; macrolides should not be used empirically in penicillin-allergic patients. 3
Test clindamycin susceptibility before use because approximately 20% of GBS isolates are resistant to clindamycin, making susceptibility testing mandatory. 10
Risk Stratification and Prognostic Factors
Older age (≥65 years), high Pitt bacteremia score (≥4), absence of fever, altered consciousness, and shock are independent predictors of 30-day mortality in GBS bacteremia. 4
Overall mortality ranges from 16–33%, with attributable mortality of 7.8–25.5%, making this a serious infection requiring aggressive management. 3, 4, 7
Underlying conditions are present in 64–70% of patients, most commonly diabetes mellitus (27.5–35%), malignancy (33%), liver disease (35%), chronic kidney disease, and alcoholism. 3, 4, 5
Nosocomial acquisition occurs in 70% of cases, and polymicrobial bacteremia (often with Staphylococcus aureus) occurs in 43% of episodes, requiring broader empiric coverage until cultures finalize. 3, 8
Surgical Considerations
Surgical debridement is required for soft tissue infections, osteomyelitis, and septic arthritis in addition to antibiotic therapy for successful treatment outcomes. 5
Drainage of abscesses and removal of infected hardware (catheters, prosthetic joints) is essential when present, as antibiotics alone are insufficient. 5
Monitoring and Follow-Up
Repeat blood cultures 48–72 hours after initiating therapy to document clearance of bacteremia; persistent bacteremia suggests endocarditis or undrained focus. 4
Continue IV antibiotics until the patient demonstrates obvious clinical improvement, fever has been absent for 48–72 hours, and no further surgical procedures are needed. 2
Monitor renal function closely when using gentamicin, especially in elderly patients, and adjust dosing based on creatinine clearance to prevent nephrotoxicity. 1
Common Pitfalls to Avoid
Do not use standard-dose penicillin (as used for Group A Streptococcus pharyngitis); GBS requires high-dose penicillin G due to higher MICs. 1, 5
Do not assume low-grade or transient bacteremia is benign; even brief bacteremia can lead to endocarditis and metastatic complications requiring prolonged therapy. 8
Do not overlook polymicrobial infection; 43% of GBS bacteremia cases involve co-pathogens (especially S. aureus), requiring empiric coverage until cultures finalize. 3, 8
Do not discharge patients early; GBS bacteremia in elderly patients carries 18.9% overall mortality and requires complete treatment courses. 7