What is the recommended approach for diagnosing and treating a strep infection?

Diagnosing and Treating Strep Infection

The recommended approach for diagnosing strep infection is to use a Rapid Antigen Detection Test (RADT) with throat culture backup for negative results in children, while adults with negative RADTs do not routinely require backup cultures due to their lower incidence of Group A Streptococcal (GAS) pharyngitis and minimal risk of rheumatic fever. 1, 2

Diagnostic Approach

When to Test

• Do not test patients with clinical features strongly suggesting viral etiology (cough, rhinorrhea, hoarseness, oral ulcers) 1
• Do not test children under 3 years old (unless they have specific risk factors like an older sibling with GAS infection) 1
• Consider testing when Centor Criteria suggest higher likelihood of GAS:
  • Fever
  • Tonsillar exudates
  • Tender anterior cervical lymphadenopathy
  • Absence of cough 2

Testing Methods

1. Rapid Antigen Detection Test (RADT)

   • High specificity (>95%) 1, 2
   • Sensitivity around 90-95% 2
   • Results available within minutes

2. Throat Culture

   • Gold standard with 90-95% sensitivity when properly performed 1
   • Results typically available in 24-48 hours
   • Should be obtained from both tonsils (or tonsillar fossae) and posterior pharynx 1

Age-Specific Testing Recommendations

• Children and adolescents: Perform RADT; negative results should be backed up with throat culture 1
• Adults: RADT alone is sufficient; backup cultures not routinely necessary due to low incidence of GAS and minimal risk of rheumatic fever 1, 2

Treatment Approach

Antibiotic Options

For confirmed GAS pharyngitis:

1. First-line treatment:

   • Penicillin V: 250 mg four times daily or 500 mg twice daily for 10 days 2, 3
   • Amoxicillin: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2, 4

2. For penicillin-allergic patients:

   • Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 2
   • Clindamycin: 300-450 mg orally three times daily for 10 days 2

Treatment Duration

• Minimum 10 days of treatment is recommended for GAS pharyngitis to prevent acute rheumatic fever 1, 4, 3
• Patients should complete the full course of antibiotics even if symptoms resolve earlier 3

Return to School/Work

• Patients should be excluded from school/work until they have completed 24 hours of appropriate antibiotic therapy 2, 5
• A study showed that 83% of patients became culture-negative within 24 hours of starting antibiotics, supporting this recommendation 5

Common Pitfalls to Avoid

1. Overdiagnosis and overtreatment: Clinical features alone cannot reliably distinguish between GAS and viral pharyngitis 1

   • Physicians often overdiagnose streptococcal pharyngitis, leading to unnecessary antibiotic use 6

2. Inadequate treatment duration: Failing to complete the full 10-day course of antibiotics increases the risk of:

   • Treatment failure
   • Development of acute rheumatic fever 4, 3

3. Testing asymptomatic contacts: Diagnostic testing or empiric treatment of asymptomatic household contacts is not routinely recommended 1, 2

4. Post-treatment testing: Follow-up cultures after treatment are not routinely recommended unless special circumstances exist 1

5. Treating viral pharyngitis with antibiotics: Using antibiotics for viral infections increases antibiotic resistance risk 3

By following these evidence-based recommendations for diagnosis and treatment, clinicians can effectively manage strep infections while minimizing unnecessary antibiotic use and preventing complications.