Diagnosis and First-Line Treatment of Group A Streptococcal Pharyngitis
In a healthy patient with suspected strep throat and no drug allergies, confirm the diagnosis with a rapid antigen detection test (RADT) followed by throat culture if negative (in children/adolescents), then treat with oral penicillin V or amoxicillin for 10 days.
Diagnostic Confirmation
Laboratory testing is mandatory before prescribing antibiotics—clinical features alone cannot reliably distinguish bacterial from viral pharyngitis. 1
Testing Strategy by Age
Adults: A negative RADT alone is sufficient to rule out Group A Streptococcus; no backup throat culture is needed because the prevalence is only 5-10% and the risk of acute rheumatic fever is extremely low. 1
Children and adolescents: A negative RADT must be confirmed with a throat culture because RADT sensitivity is only 80-90%, missing 10-20% of true infections, and this age group has higher prevalence (20-30%) and greater risk of rheumatic fever. 1
Positive RADT: No culture needed—specificity is ≥95%, making false positives rare. 1
When to Test
Perform testing when patients present with:
- Sudden-onset sore throat
- Fever
- Tonsillopharyngeal erythema with exudate
- Tender anterior cervical lymphadenopathy
- Absence of viral features (cough, rhinorrhea, hoarseness, conjunctivitis) 1, 2
Do not test children under 3 years old except when an older sibling has confirmed Group A Streptococcus, because strep pharyngitis and rheumatic fever are rare in this age group. 1
First-Line Antibiotic Regimen
Penicillin V or amoxicillin for a full 10-day course is the definitive first-line treatment, offering proven efficacy, narrow spectrum, excellent safety, and low cost, with no documented penicillin resistance in Group A Streptococcus worldwide. 3, 4
Specific Dosing
Penicillin V:
- Children <27 kg: 250 mg orally 2-3 times daily for 10 days 1
- Children ≥27 kg and adults: 500 mg orally 2-3 times daily for 10 days 1
Amoxicillin (preferred for better palatability and once-daily dosing):
- Children: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
- Adults: 500 mg twice daily or 1000 mg once daily for 10 days 4
Intramuscular benzathine penicillin G (when adherence is uncertain):
Why 10 Days Is Mandatory
A complete 10-day course is essential to achieve maximal pharyngeal eradication and prevent acute rheumatic fever—shortening the course by even a few days dramatically increases treatment failure rates and rheumatic fever risk, even if symptoms resolve within 3-4 days. 3, 1, 4
Treatment can be safely delayed up to 9 days after symptom onset and still prevent rheumatic fever, allowing time for culture confirmation without compromising outcomes. 3, 1
Common Pitfalls to Avoid
Do not prescribe antibiotics based on clinical appearance alone—up to 70% of patients with sore throat receive unnecessary antibiotics, while only 20-30% of children and 5-10% of adults actually have Group A Streptococcus. 1
Do not test or treat asymptomatic household contacts—up to one-third may be asymptomatic carriers, and prophylactic treatment does not reduce subsequent infection rates. 1
Do not order routine follow-up cultures in asymptomatic patients after completing therapy—positive post-treatment tests often reflect carrier status rather than treatment failure. 3, 1
Do not shorten the antibiotic course below 10 days (except azithromycin's 5-day regimen)—this markedly increases treatment failure and rheumatic fever risk. 1, 4
Timing of Contagiousness
Patients are generally non-contagious after 24 hours of appropriate antibiotic therapy and can return to school or work at that time. 4, 5
When to Reassess
If symptoms worsen or persist beyond 5 days after starting appropriate antibiotics, reassess for suppurative complications (peritonsillar abscess, cervical lymphadenitis) or alternative diagnoses. 1, 2