What are the diagnostic criteria and treatment options for strep throat?

Diagnostic Criteria and Treatment Options for Strep Throat

The diagnosis of strep throat should be based on the Centor Criteria (tonsillar exudates, tender anterior cervical lymph nodes, lack of cough, and fever), followed by laboratory confirmation with rapid antigen detection test (RADT) and/or throat culture, with treatment consisting of penicillin or amoxicillin for 10 days as first-line therapy. 1

Diagnostic Criteria

Clinical Assessment

• Use the Centor Criteria to assess the likelihood of Group A Streptococcal (GAS) pharyngitis:

  1. Tonsillar exudates
  2. Tender anterior cervical lymph nodes
  3. Lack of cough
  4. Fever 1

• Clinical presentation typically includes:

  • Abrupt onset of sore throat
  • Fever and chills
  • Malaise and headache
  • Pharyngeal or tonsillar exudate 2

• Signs suggesting viral rather than streptococcal etiology:

  • Presence of cough
  • Coryza (nasal discharge)
  • Conjunctivitis
  • Diarrhea 2

Testing Algorithm

Based on Centor Criteria score:

• Score 0-1: Likely viral cause, no testing needed
• Score 2-3: Consider RADT
• Score 4: High likelihood of GAS, consider empiric treatment or testing 1

Laboratory Confirmation

1. Rapid Antigen Detection Test (RADT):

   • Quick results (minutes)
   • High specificity but lower sensitivity than culture 3, 1
   • Negative RADT should be confirmed with throat culture, especially in children and adolescents 4

2. Throat Culture:

   • Gold standard for diagnosis 3, 2
   • Results take 24-48 hours
   • Higher sensitivity than RADT 5

Treatment Options

First-Line Antibiotic Therapy

• Penicillin V or Amoxicillin for 10 days 1, 6
  • Penicillin remains drug of choice due to:
    • Narrow spectrum of activity
    • Long-standing proven efficacy
    • No documented resistance
    • Cost-effectiveness 7
  • Amoxicillin dosage: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1

Alternative Antibiotics for Penicillin-Allergic Patients

• First-generation cephalosporins (for non-anaphylactic penicillin allergy) 1, 4
• Clindamycin: 300-450 mg orally three times daily for 10 days 1
• Azithromycin: 12 mg/kg once daily (max 500 mg) for 5 days 1, 8
  • Note: Some regions report significant resistance to azithromycin 4
  • Azithromycin should not be relied upon for prevention of rheumatic fever 8

Important Treatment Considerations

• Complete the full 10-day course of antibiotics (except for 5-day azithromycin) to prevent complications such as acute rheumatic fever 1, 6
• Patients should complete at least 24 hours of antibiotics before returning to school or work to reduce transmission risk 1
• Monitor for treatment failure - patients with worsening symptoms after antibiotic initiation or symptoms lasting 5+ days after starting treatment should be reevaluated 4

Symptomatic Relief

• NSAIDs are more effective than acetaminophen for fever and pain 1
• Medicated throat lozenges used every two hours 1
• Cold liquids or ice chips, gargling with cold water 1
• Avoid hot liquids and spicy foods that may irritate the throat 1

Prevention of Complications

• Primary goal of treatment is to prevent:

  1. Acute rheumatic fever
  2. Suppurative complications
  3. Reduction in transmission of GAS 3, 7

• Continuous antimicrobial prophylaxis is recommended for patients with a history of rheumatic fever to prevent recurrences 1, 7

• Tonsillectomy is rarely recommended as a preventive measure, only considered for:

  • ≥7 episodes of streptococcal pharyngitis in 1 year, OR
  • ≥5 episodes per year for 2 consecutive years, OR
  • ≥3 episodes per year for 3 consecutive years 1, 4

Common Pitfalls to Avoid

• Treating viral pharyngitis with antibiotics - only 10% of adults with sore throat have GAS pharyngitis, yet 60% or more receive antibiotics 4
• Relying solely on clinical presentation without laboratory confirmation 3, 5
• Incomplete antibiotic courses increasing the risk of complications and antibiotic resistance 6
• Using broad-spectrum antibiotics when narrow-spectrum options are effective 7
• Failing to confirm negative RADT with throat culture in children and adolescents 4