In a patient with streptococcal bacteremia, which Lancefield groups are most common and what empiric antibiotic regimen should be started (including alternatives for severe penicillin allergy and possible endocarditis)?

Group A Streptococcal Bacteremia: Common Lancefield Groups and Empiric Antibiotic Management

Most Common Lancefield Groups in Streptococcal Bacteremia

Group B streptococci are the most common cause of streptococcal bacteremia (50%), followed by Group G (22.9%), Group A (23.6%), and Group C (3.6%). 1

• Group A (Streptococcus pyogenes) accounts for approximately 23.6% of beta-hemolytic streptococcal bacteremia cases 1
• Group B streptococci represent the single largest proportion at 50% of cases 1
• Group G streptococci (Streptococcus dysgalactiae subspecies equisimilis) cause 22.9% of cases, predominantly in elderly patients (median age 76 years) with underlying diseases 1, 2
• Group C streptococci are relatively uncommon at 3.6% of bacteremia cases 1, 3

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Empiric Antibiotic Regimen for Streptococcal Bacteremia

First-Line Therapy (No Penicillin Allergy)

Initiate intravenous penicillin G 2–4 million units every 4–6 hours or ceftriaxone 2 g IV once daily immediately upon suspicion of streptococcal bacteremia. 4

• Penicillin G or ceftriaxone remain the drugs of choice for all beta-hemolytic streptococcal infections, with no documented penicillin resistance worldwide among Group A streptococci 4, 5
• Duration: 4 weeks for uncomplicated bacteremia; 4–6 weeks for Group A, B, C, or G streptococcal endocarditis 4
• Add gentamicin for the first 2 weeks when treating Group B, C, or G streptococcal endocarditis: penicillin or ceftriaxone plus gentamicin 1 mg/kg IV every 8 hours 4

Severe Penicillin Allergy (Immediate/Anaphylactic Reactions)

For patients with anaphylaxis, angioedema, or urticaria to penicillin, prescribe vancomycin 15 mg/kg IV every 12 hours (adjust for renal function) for 4–6 weeks. 4

• Vancomycin is the only recommended alternative for severe penicillin allergy in streptococcal bacteremia, as cephalosporins carry up to 10% cross-reactivity risk with immediate penicillin hypersensitivity 4, 5
• Do not add gentamicin to vancomycin regimens for streptococcal endocarditis, as the combination provides no additional benefit 4
• Vancomycin should not be used when beta-lactam–susceptible streptococci are confirmed, as it has higher failure rates and slower bacteremia clearance than penicillin or ceftriaxone 4

Non-Immediate (Delayed) Penicillin Allergy

First-generation cephalosporins such as cefazolin 2 g IV every 8 hours are safe and effective alternatives for patients with delayed, non-anaphylactic penicillin reactions. 4, 5

• Cross-reactivity risk is only 0.1% with delayed penicillin reactions 5, 6
• Cefazolin provides excellent streptococcal coverage and is preferred over vancomycin when beta-lactams can be safely administered 4

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Special Considerations for Possible Endocarditis

Diagnostic Evaluation

Obtain transesophageal echocardiography (TEE) in all patients with streptococcal bacteremia to identify endocarditis, as this determines treatment duration (4 weeks vs. 4–6 weeks). 4

• TEE has superior sensitivity compared to transthoracic echocardiography and should be performed unless contraindicated 4
• Patients with negative TEE results who have had their catheter or infection source removed should receive 14 days of systemic antibiotic therapy 4

Endocarditis Treatment Modifications

If endocarditis is confirmed, extend therapy to 4–6 weeks and consider adding gentamicin for the first 2 weeks when treating Group B, C, or G streptococcal endocarditis. 4

• For Group A (S. pyogenes) endocarditis: penicillin G IV for 4–6 weeks is reasonable; ceftriaxone is an acceptable alternative 4
• For Group B, C, and G streptococcal endocarditis: add gentamicin to penicillin or ceftriaxone for at least the first 2 weeks of a 4–6 week course 4
• Early cardiac surgical intervention may improve survival in beta-hemolytic streptococcal endocarditis, particularly for Group A infections 4

Prosthetic Valve Endocarditis

Prosthetic valve endocarditis caused by streptococci requires 6 weeks of therapy with penicillin or ceftriaxone, with or without gentamicin for the first 2 weeks. 4

• For highly penicillin-susceptible strains (MIC ≤0.12 μg/mL), 6 weeks of penicillin or ceftriaxone with optional gentamicin for 2 weeks is recommended 4
• For relatively resistant strains (MIC >0.12 μg/mL), 6 weeks of penicillin or ceftriaxone plus gentamicin for the entire duration is required 4

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Common Pitfalls to Avoid

• Do not use vancomycin when beta-lactam antibiotics can be safely administered, as vancomycin has inferior efficacy and slower bacteremia clearance for streptococcal infections 4
• Do not prescribe cephalosporins to patients with immediate/anaphylactic penicillin reactions due to the ~10% cross-reactivity risk 4, 5, 6
• Do not omit TEE in streptococcal bacteremia, as undiagnosed endocarditis will be undertreated with shorter antibiotic courses 4
• Do not shorten therapy below 4 weeks for bacteremia or 4–6 weeks for endocarditis, even if clinical improvement occurs earlier 4

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Clinical Context and Outcomes

• Group C and G streptococcal bacteremia carry high mortality rates (15–25%), especially in elderly patients with underlying cardiovascular disease or malignancy 1, 2, 3
• Delayed diagnosis of endovascular infections (endocarditis, infected thrombi) contributes to poor outcomes 1, 3
• Most Group G bacteremia cases are community-acquired (88%) and occur in patients over 60 years old with underlying diseases 2
• Prior animal exposure is reported in approximately 24% of Group C streptococcal bacteremia cases 3