What is the diagnostic and treatment approach for streptococcal pharyngitis using the Centor score?

Diagnostic and Treatment Approach for Streptococcal Pharyngitis Using the Centor Score

The Centor score is an effective clinical decision tool for diagnosing group A streptococcal pharyngitis, with patients scoring 3-4 criteria having a 28-53% risk of streptococcal infection and should be considered for rapid antigen testing, while antibiotics should be withheld in patients with scores of 0-2 due to low probability of streptococcal infection. 1, 2

Centor Score Components and Interpretation

• The Centor score consists of four clinical features: fever by history, tonsillar exudates, tender anterior cervical adenopathy, and absence of cough 1, 2

• Risk of group A streptococcal infection increases with the number of criteria present 1:

  • 4 criteria: 51-56% risk
  • 3 criteria: 28-35% risk
  • 2 criteria: 11-17% risk
  • 1 criterion: 5-10% risk
  • 0 criteria: 1-2.5% risk

• The modified Centor score (McIsaac) adds age as a criterion, validated in both adults and children (3-15 years old) 1

• The utility of Centor criteria appears lower in children than adults due to different clinical presentation in the first years of life 2

Diagnostic Algorithm

1. Clinical Assessment with Centor Score 1, 2:

   • Count the number of criteria present (fever, tonsillar exudate, tender cervical adenopathy, absence of cough)
   • Stratify patients based on total score

2. Testing Recommendations Based on Score 1, 2:

   • Scores 0-2: No testing needed (low probability of streptococcal infection)
   • Scores 3-4: Consider rapid antigen testing (RAT)

3. Interpretation of Test Results 1, 3:

   • If RAT is performed, throat culture is not necessary after a negative RAT in adults
   • RAT has high specificity (≥95%) but variable sensitivity (86-95%)
   • RAT should be performed by trained staff on both the posterior pharyngeal wall and tonsils for maximum accuracy

Treatment Approach

1. For Patients with Low Centor Scores (0-2) 1, 2:

   • Antibiotics should not be used
   • Provide symptomatic relief with either ibuprofen or paracetamol

2. For Patients with High Centor Scores (3-4) 1, 2:

   • If RAT is positive: Consider antibiotic therapy
   • If RAT is negative: No antibiotics needed (in adults)
   • Weigh modest benefits of antibiotics against side effects, impact on microbiota, increased antibiotic resistance, medicalization, and costs

3. Antibiotic Selection When Indicated 1, 2:

   • Penicillin V is the recommended first-line treatment, twice or three times daily for 10 days
   • Azithromycin can be considered as an alternative in penicillin-allergic patients 4

Important Considerations and Pitfalls

• Test Performance Variability: The accuracy of RAT depends on the skill and experience of the person obtaining the throat swab 1, 3
• Spectrum Bias: RAT performance varies based on the clinical characteristics of patients selected for testing 1
• Low Positive Predictive Value: Even with high Centor scores (3-4), the positive predictive value is only around 48%, meaning clinical scoring alone is insufficient for definitive diagnosis 5, 6
• Recent Evidence: A 2024 systematic review found that both Centor and McIsaac scores are equally ineffective at triaging patients with pharyngitis in hospital settings, with high thresholds missing true positive cases and low thresholds leading to antibiotic overprescription 7
• Prevention of Complications: The prevention of suppurative complications is not a specific indication for antibiotic therapy in sore throat 1

Special Populations

• Children: In children, a negative RAT should be confirmed with a throat culture due to higher prevalence of strep infections and risk of complications 3
• Adults: Confirmation of a negative RAT with throat culture is generally not necessary due to lower incidence of streptococcal infection and extremely low risk of rheumatic fever 3

By following this evidence-based approach using the Centor score and appropriate testing, clinicians can more accurately diagnose streptococcal pharyngitis and make informed decisions about antibiotic therapy, ultimately reducing unnecessary antibiotic use while ensuring appropriate treatment for those who need it.