Treatment of Streptococcus agalactiae Bacteremia
For Streptococcus agalactiae (Group B Streptococcus) bacteremia in adults, initiate intravenous penicillin G or ampicillin as first-line therapy, with treatment duration of 2-4 weeks depending on source and complications. 1
Initial Antibiotic Selection
Penicillin remains the drug of choice for GBS bacteremia, as all strains maintain 100% susceptibility to penicillin and ampicillin. 2, 3 The recommended regimens include:
- Penicillin G 12-18 million units/day IV in divided doses for uncomplicated bacteremia 1
- Ampicillin is equally effective and may be preferred in some settings given its broader availability 3
- Ceftriaxone 2g IV once daily is an acceptable alternative for penicillin-susceptible strains 1
For penicillin-allergic patients, vancomycin is the most reliable alternative, as resistance has not been documented. 2 This is critical because erythromycin resistance rates reach 25% and clindamycin resistance 13% in recent surveillance data. 2
Treatment Duration Based on Source
The duration of therapy must be tailored to the infection source and presence of complications:
- Uncomplicated bacteremia: 2 weeks minimum 4
- Complicated bacteremia with metastatic foci: 4-6 weeks 4
- Endocarditis: 4 weeks for native valve, 6 weeks for prosthetic material 4, 1
- Meningitis: 2-3 weeks (though this is more common in neonates) 5
Critical Source Control Measures
Identify and address the anatomical source within 12 hours of diagnosis. 4 Common portals of entry in adults include:
- Skin and soft tissue infections (most common at 24.4% of cases, particularly in women) 6
- Urinary tract (more common in men, requires evaluation for structural abnormalities) 3, 6
- Bone and joint infections (more common in women) 6
- Primary bacteremia (50% of cases have no identifiable source) 6
If intravascular catheters are present, remove them promptly after establishing alternative access, as catheter-associated GBS bacteremia may not resolve until the device is removed. 4
Essential Monitoring Requirements
Obtain repeat blood cultures 2-4 days after initiating therapy to document clearance. 1 This is particularly important because:
- GBS bacteremia typically clears within several days of appropriate therapy 4
- Persistent bacteremia suggests inadequate source control or endocarditis 4
Perform echocardiography on all patients with streptococcal bacteremia to exclude endocarditis, especially in those with underlying cardiac disease, prolonged bacteremia, or no obvious source. 1
High-Risk Populations Requiring Intensified Management
Elderly patients (≥60 years account for 62% of cases) and those with underlying conditions face higher mortality risk (overall 18.9%, attributable 7.8%). 6 Specific risk factors include:
- Liver disease (more common in males) 6
- Malignancy (more common in females) 6
- Diabetes mellitus 6
- Immunocompromised states 2
Common Pitfalls to Avoid
Do not use erythromycin or clindamycin empirically for penicillin-allergic patients without susceptibility testing, given resistance rates of 25% and 13% respectively. 2 Use vancomycin instead until sensitivities are available.
Do not assume uncomplicated bacteremia without thorough evaluation for metastatic foci, including skin examination, joint assessment, and urinary tract evaluation, as these determine treatment duration. 3, 6
In women, always evaluate the genitourinary tract as a potential reservoir, as the vagina serves as a colonization site that may require local treatment in addition to systemic antibiotics for successful eradication. 7, 3