Modified Centor Score (McIsaac) for Strep Pharyngitis

In children and adults with sore throat, should a clinical scoring system be used to determine who should be tested for GAS? 

On October 14, 2025, the Infectious Diseases Society of America (IDSA) released a Part 1 update to the 2012 IDSA Guideline on Diagnosis and Management of Group A Streptococcal (GAS) Pharyngitis. The IDSA include recommendations on risk assessment for GAS using clinical scoring systems in children and adults. In children and adults with sore throat, the IDSA suggest using a clinical scoring system to determine who should be tested for GAS. The Modified/McIsaac Score, an adaptation of the Centor Score, is one of the tools recommended. 

The IDSA emphasizes the following remarks in the 2025 Part 1 update:

1. Clinical scoring systems are most helpful in identifying patients with low probability of GAS pharyngitis, in whom further evaluation by diagnostic testing is unlikely to be helpful. 
2. High-risk individuals should be strongly considered for testing even if their clinical scores are low. Examples of high-risk individuals include those presenting with sore throat who have had household exposure to GAS (e.g., living or sleeping in the same indoor shared space as a person diagnosed with GAS infection), a history of a previous rheumatic fever diagnosis, or symptoms or signs suggestive of complicated local or systemic GAS infection (e.g., peritonsillar or retropharyngeal abscess, scarlet fever and/or toxic shock syndrome). 
3. Given the lack of evidence favoring any particular scoring system, clinicians and patients may favor clinical scoring systems that do not include laboratory test(s).   
4. The recommendation to use a scoring system does not apply to children under three years of age as GAS infection in this age group may not present with typical clinical features represented in these scoring systems.

Usage 
 

The Centor Score assists clinicians in identifying patients that are at higher risk for strep pharyngitis. The latest 2012 guidelines from the IDSA (Infectious Disease Society of America) recommends testing patients that are at higher risk for strep pharyngitis. Additionally, not to give antibiotics until a rapid test is positive or a throat culture is positive. Guidelines no longer recommend empiric treatment for patients alone.

Most cases of pharyngitis are viral. The incidence of rheumatic fever is rare. Additionally, early antibiotics to prevent complications, such as peritonsillar abscess is questionable in the general population. Therefore, antibiotic stewardship is essential to preventing harm (i.e. resistance) from overprescribing.

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Summary 
 

The Centor Score assists in risk stratifying patients when there is concern for strep pharyngitis. The Modified/McIsaac Score includes an age component.

Rules

Interpretation

Management Considerations:

• Steroids (i.e. dexamethasone) and NSAIDS can be used to provide symptom relief and resolution similar to antibiotics.
• Antibiotics do not prevent the suppurative complications (i.e. peritonsillar abscess) of streptococcal pharyngitis.
• Carefully consider other etiologies (below) when a patient presents with symptoms greater than 3 days or red flag symptoms.
  • Peritonsillar abscess
  • Lemierre Syndrome
  • Viral infections in adult populations (mononucleosis or acute HIV)

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• Use only in patients with a recent onset of 3 or more days of acute pharyngitis.
• The recommendation to use a scoring system does not apply to children under three years of age as GAS infection in this age group may not present with typical clinical features represented in these scoring systems.