What is the difference in treatment between Strep A (Streptococcus pyogenes) and Strep B (Streptococcus agalactiae) throat infections?

Strep A vs Strep B in Throat Infections

Group A Streptococcus (Streptococcus pyogenes) is the primary bacterial pathogen requiring diagnosis and antibiotic treatment in pharyngitis, while Group B Streptococcus (Streptococcus agalactiae) rarely causes pharyngitis and does not require the same diagnostic or therapeutic approach. 1, 2

Clinical Significance and Pathogenicity

Group A Streptococcus (GAS) is the only bacterial pharyngeal pathogen that mandates specific etiologic diagnosis and treatment because it can trigger serious post-infectious complications including acute rheumatic fever and post-streptococcal glomerulonephritis. 3 The primary goal of treating GAS pharyngitis is preventing acute rheumatic fever, not merely providing symptomatic relief. 2, 4

Group B Streptococcus (GBS), in contrast, was historically an animal pathogen that has shifted toward causing human infections, but these are predominantly invasive infections in neonates, pregnant women, and immunocompromised adults—not pharyngitis. 5 GBS pharyngitis is exceedingly rare and does not cause rheumatic fever or require the same treatment protocols as GAS. 2

Diagnostic Approach

For Suspected GAS Pharyngitis

• Laboratory confirmation is mandatory because clinical symptoms of GAS and viral pharyngitis overlap extensively. 2
• Use rapid antigen detection test (RADT) or throat culture in patients with clinical features suggesting bacterial infection (sudden onset, intense sore throat, fever, tonsillar exudate, tender anterior cervical lymph nodes, absence of cough/coryza). 1, 3
• In adults, a negative RADT is sufficient to rule out streptococcal pharyngitis without confirmatory culture. 2
• In children, confirm negative RADT with throat culture due to higher prevalence and rheumatic fever risk. 2
• RADTs have excellent specificity (≥95%) but sensitivity of 80-90%, meaning positive tests are reliable but negative tests require culture backup in children. 1, 6

For GBS

• Do not routinely test for GBS in pharyngitis, as it is not a clinically significant pharyngeal pathogen requiring treatment. 5
• Standard throat culture methods using bacitracin disk testing differentiate GAS from other β-hemolytic streptococci (≥95% of GAS show inhibition zones). 1

Treatment Protocols

Group A Streptococcus Treatment

For patients without penicillin allergy:

• Oral penicillin V or amoxicillin for 10 days is the standard of care. 1, 2, 4
• Amoxicillin (50 mg/kg/day once daily, maximum 1000 mg) offers improved adherence with once-daily dosing. 2
• Intramuscular benzathine penicillin G (600,000 U for <27 kg; 1,200,000 U for ≥27 kg) as single dose for patients unlikely to complete oral therapy. 1, 2, 4

For non-anaphylactic penicillin allergy:

• First-generation cephalosporins (cephalexin 20 mg/kg twice daily or cefadroxil 30 mg/kg once daily) for 10 days. 7, 2
• Up to 10% cross-reactivity exists with immediate penicillin hypersensitivity, so avoid cephalosporins in those patients. 1, 7

For immediate/anaphylactic penicillin allergy:

• Clindamycin 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days. 7, 2
• Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days—the only antibiotic requiring less than 10 days due to prolonged tissue half-life. 7, 2
• Clarithromycin 7.5 mg/kg twice daily (maximum 250 mg per dose) for 10 days. 7, 2

Critical duration requirement: The 10-day course is necessary for maximal pharyngeal eradication with most antibiotics and prevention of acute rheumatic fever. 1, 2, 4 Therapy can be safely postponed up to 9 days after symptom onset and still prevent rheumatic fever. 1, 7

Group B Streptococcus

No specific pharyngitis treatment protocol exists for GBS because it does not cause the clinical syndrome of streptococcal pharyngitis requiring intervention. 5 If GBS is incidentally isolated from a throat culture, it does not warrant antibiotic treatment in the context of pharyngitis.

Post-Treatment Management

For GAS

• Do not perform routine follow-up throat cultures after completing therapy in asymptomatic patients. 1, 2, 4
• Follow-up testing is justified only in special circumstances: patients with history of rheumatic fever, community outbreaks of rheumatic fever or post-streptococcal glomerulonephritis. 1, 4
• Patients become non-contagious after 24 hours of appropriate antibiotic therapy. 2, 4, 8

For GBS

• No follow-up testing or treatment protocols apply, as GBS pharyngitis is not a recognized clinical entity requiring management. 5

Common Pitfalls to Avoid

• Never treat pharyngitis based on clinical symptoms alone without laboratory confirmation—this leads to massive antibiotic overuse. 2
• Do not use trimethoprim-sulfamethoxazole (Bactrim) for strep throat—it has high resistance rates (50%) and does not eradicate GAS. 7
• Do not confuse Group C and Group G streptococcal pharyngitis with GAS—these do not cause rheumatic fever and do not require the same treatment approach. 2, 5
• Do not test or treat asymptomatic household contacts of GAS pharyngitis patients. 2
• Do not prescribe shorter courses than recommended (except azithromycin's 5-day regimen)—this leads to treatment failure and complications. 7, 2