What are the diagnostic criteria and treatment for strep throat in a teenager using the Centor criteria (Clinical prediction rule for Group A Streptococcal pharyngitis)?

Centor Criteria for Strep Throat in Teenagers

The Centor criteria are an essential clinical prediction tool for diagnosing Group A Streptococcal (GAS) pharyngitis in teenagers, with a score of 3-4 criteria indicating a 28-56% risk of streptococcal infection and warranting either rapid antigen detection testing or empiric antibiotic treatment. 1, 2

Centor Criteria Components

The Centor criteria include four clinical features:

1. Tonsillar exudates (white or yellow coating on tonsils)
2. Tender anterior cervical lymphadenopathy (swollen, painful lymph nodes in neck)
3. Absence of cough
4. History of fever (>100.4°F/38°C)

Each criterion present adds one point to the score (0-4 points total).

Modified Centor Score (McIsaac Score)

For teenagers, the Modified Centor Score adds an age criterion to the original four components:

• Age 3-14 years: +1 point
• Age 15-44 years: 0 points
• Age ≥45 years: -1 point

This modification improves diagnostic accuracy by accounting for the higher prevalence of GAS in children and adolescents. 1, 2

Risk Stratification Based on Centor Score

Centor Score	Risk of GAS Infection	Recommended Approach
0-1	1-10%	No testing or antibiotics needed
2	11-17%	Consider RADT; treat if positive
3	28-35%	Perform RADT; treat if positive
4	51-56%	Consider empiric treatment or perform RADT

1, 2

Diagnostic Testing Recommendations

When to Test

• Score 0-1: No testing recommended (low probability of GAS)
• Score 2-4: Perform Rapid Antigen Detection Test (RADT)

Testing Considerations

• RADT has high specificity (≥95%) but variable sensitivity (~90%)
• In teenagers, a negative RADT should be backed up by throat culture due to:
  • Higher prevalence of GAS in this age group
  • Risk of acute rheumatic fever if GAS is missed
• Proper throat swab technique is crucial: sample both tonsils and posterior pharyngeal wall 1, 2

Treatment Recommendations

If GAS is confirmed:

• First-line treatment: Penicillin V or amoxicillin for 10 days

  • Penicillin remains drug of choice due to narrow spectrum, low cost, and effectiveness
  • Amoxicillin is equally effective and more palatable

• For penicillin-allergic patients:

  • Non-anaphylactic allergy: First-generation cephalosporin for 10 days
  • Anaphylactic allergy: Clindamycin or clarithromycin for 10 days, or azithromycin for 5 days 1, 3

• Adjunctive therapy:

  • Acetaminophen or ibuprofen for pain/fever management
  • Avoid aspirin in teenagers due to risk of Reye syndrome 1

Clinical Pearls and Pitfalls

Features Suggesting Viral Etiology (Against GAS)

• Cough
• Rhinorrhea (runny nose)
• Hoarseness
• Conjunctivitis
• Oral ulcers
• Diarrhea 1, 2, 4

Additional Clinical Sign to Consider

Recent research suggests that palatal petechiae (small red spots on the roof of the mouth) may be a significant predictor of GAS pharyngitis not included in the Centor criteria. In one study, 75% of patients with palatal petechiae had positive throat cultures for GAS. 5

Common Pitfalls

1. Over-reliance on clinical features alone without confirmatory testing
2. Treating viral pharyngitis with antibiotics (70% of sore throats receive antibiotics, but only 20-30% are due to GAS)
3. Poor swabbing technique leading to false-negative results
4. Failure to recognize carriers versus acute infection 1, 2

Conclusion

The Centor criteria provide a valuable clinical prediction tool for assessing the likelihood of GAS pharyngitis in teenagers. When combined with appropriate testing (RADT with culture backup for negative results), this approach helps optimize antibiotic use while ensuring appropriate treatment of true GAS infections to prevent complications like acute rheumatic fever.