Calculated Decisions | Diagnosis and Management of Group A Streptococcal Pharyngitis

Diagnosis and Management of Group A Streptococcal Pharyngitis and Associated Complications

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Calculated Decisions

Centor Score
Centor Score (Modified/McIsaac) for Strep Pharyngitis
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Centor Score (Modified/McIsaac) for Strep Pharyngitis

The Centor Score estimates the probability that pharyngitis is streptococcal and suggests the management course.
Points & Pearls 
  • The Centor Score correlates directly with the risk of a throat culture that is positive for group A Streptococcus (GAS).
  • The most recently updated guideline from the Infectious Diseases Society of America for diagnosis and management of GAS pharyngitis no longer recommends empiric treatment. The new recommendation is to test patients who are at higher risk for GAS pharyngitis, but give antibiotics only when a patient’s rapid antigen detection test or throat culture is positive for GAS (Shulman et al 2012).
  • The modified criteria designated by McIsaac et al (2004) include an age component, along with tonsillar swelling. GAS is incredibly rare in patients aged < 3 years, and is also less common in older adults, so the age component can help clinicians risk stratify patients.
  • Most cases of pharyngitis are viral in origin. Given the rare incidence of acute rheumatic fever, along with the questionable benefits of early antibiotics to prevent sequelae like peritonsillar abscess, antibiotics are now prescribed much less often. Steroids (such as dexamethasone) and NSAIDs (nonsteroidal anti-inflammatory drugs) often provide similar pain relief and resolution of symptoms to antibiotics.

Why and When to Use, and Next Steps 

Why to Use

Most pharyngitis is viral and does not respond to antibiotic treatment. The Centor Score attempts to predict which patients will have culture-confirmed GAS infections of the pharynx, to help determine which patients to test in the first place.

The newer FeverPAIN Score is similar, but the Centor Score has the advantage of distinguishing adolescents and young adults from preadolescents, which is important because streptococcal carrier rates for preadolescents are higher than for adolescents and young adults, and older patients exhibit more severe symptoms and develop suppurative complications more frequently (Mitchell et all 2011).

When to Use

  • For use in children with pharyngitis, primarily; the risk of GAS decreases significantly with age into adulthood.

  • Use only in patients with recent onset (≤ 3 days) of acute pharyngitis.

Next Steps

Steroids and NSAIDs improve symptoms; antibiotics are often indicated in GAS pharyngitis, but do not prevent its suppurative complications, such as peritonsillar abscess.


Calculator Review Authors 

Graham Walker, MD  

Department of Emergency Medicine

Kaiser Permanente San Francisco 

San Francisco, CA

Rachel Kwon, MD


Critical Actions

It is still important to carefully consider patients with symptom duration longer than 3 days, even though the Centor Score does not apply. While symptoms are not compatible with a diagnosis of acute pharyngitis, these patients require evaluation for suppurative complications (eg, peritonsillar abscess or Lemierre syndrome), or viral infections in adult patients (eg, infectious mononucleosis or acute HIV) (Centor 2017).

Evidence Appraisal

The goal of the original study by Centor et al was to develop criteria to diagnose GAS infection in adult patients presenting to the emergency department with a sore throat (Centor et al 1981). The original model designated 4 criteria: tonsillar exudates; swollen, tender anterior cervical nodes; absence of cough; and history of fever. Patients exhibiting all 4 variables had a 56% probability of having a group A beta strep-positive culture; the probability was 32% in patients with 3 variables, 15% in patients with 2 variables, 6.5% in patients with 1 variable, and 2.5% in patients with none of the variables.

The Centor Score was later modified to include age (McIsaac et al 1998) and was validated (McIsaac et al 2004) for use in both children and adults presenting with a sore throat. McIsaac et al (1998) determined that using the Centor Score would reduce the number of unnecessary initial antibiotic prescriptions by 48%, without increasing throat culture use.

The Centor Score and its modifications were derived in relatively small samples (n = 286 and n = 521, respectively). In order to more precisely classify the risk of GAS infection, Fine et al (2012) performed a national-scale validation of the score on a geographically diverse population of > 140,000 patients presenting in a clinical setting. The study was carried out over the course of more than a year, mitigating any impact of seasonality of GAS incidence on the results. This analysis provided more precise interpretations of risk for each category of the Centor Score and still fell within the 95% confidence interval of the original study by Centor et al (1981), which had a much smaller sample size.

In their comparison of the Centor Score with other identification and treatment strategies, McIsaac et al (2004) found that use of the score resulted in fewer overall tests (throat cultures and rapid antigen detection tests) per person, but more throat cultures (96.1% of adults) than other strategies. As a result, the Centor Score represented a compromise, requiring the least diagnostic testing, providing 100% sensitivity and greater than 90% specificity in both children and adults, and producing significant reductions in unnecessary use of antibiotics, compared with other strategies.

Harris et al (2016) encouraged the use of the Centor Score primarily to identify patients with a low probability of GAS pharyngitis who do not warrant further testing, citing the low positive predictive value of the criteria.

Calculator Creator

Robert M. Centor, MD

Read more about Dr. Centor.


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Publication Information

Michelle N. Vazquez, MD; Jennifer E. Sanders, MD

Publication Date

December 2, 2017

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