Streptococcal Pharyngitis:

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By Jolien Aalbers University of Nijmegen

• Streptococcal Pharyngitis
• A Systematic Review of the Predictive Value of
  Signs and Symptoms and the External Validation of
  the Centor Score CPR

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Outline

• Background
• Methods1. Diagnostic accuracy of signs and
  symptoms2. Validation of the Centor Score
• Results1. Diagnostic accuracy of signs and
  symptoms2. Validation of the Centor Score

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Background

• Group A ß-haemolytic Streptococcal (GABHS)
  pharyngitis can lead to serious complications
• GABHS infection is the only indication for
  treatment with antibiotics
• Antibiotic resistance is an important public
  health issue
• A prediction rule to reduce unnecessary
  antibiotic prescriptions would help to decrease
  antibiotic resistance

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Clinical prediction rule

• A tool that quantifies the contribution of
  symptoms, clinical signs and available diagnostic
  tests to stratify patients according to the
  probability of having a target disorder
• The outcome can have a diagnostic, prognostic
  or therapeutic value

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Levels of evidence for the development of a CPR
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The Centor Score

• 4 items 1. Tonsillar exudate
• 2. Tender cervical anterior adenopathy
• 3. History of fever (or gt38.0?C)
• 4. Absence of cough
• Cumulative score (0-4 points) 0. 2.5
• (post-test probabilities) 1. 6.5 (6.0-6.9)
• 2. 15.4 (14.1-16.6)
• 3. 31.6 (30.1-34.1)
• 4. 55.7

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Other diagnostic tests

• Throat swab gold standard
• Takes 24-48 hours for results
• Expensive
• A proportion of patients with positive cultures
  are carriers
• Rapid Antigen Detection Test (RADT)
• Not as sensitive as the throat swab
• Possible lack of cost-effectiveness

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Study methods (1)

• Search strategy
• PubMed, EMBASE, Cochrane database, Google Scholar
  and MEDION
• Hand-checking references of filtered papers
• Inclusion and exclusion-criteria
• Population participants were recruited upon 1st
  presentation from an ambulatory care setting with
  sore throat as their main presenting complaint,
  and had to be at least 15 years of age or older

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Study methods (2)

• Study design the studies had to assess either
  the diagnostic accuracy of signs and symptoms
  and/or apply the Centor score
• Reference standard a throat swab
• Retrospective and prospective studies were
  included
• No criteria were set for the size of the
  population
• Quality assessment modified QUADAS tool
• (QUality Assessment of Diagnostic Accuracy
  Studies)

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Methods (3) data extraction and analysis of
diagnostic accuracy of signs and symptoms

• Signs and symptoms Exudate
• Absence of cough
• Fever (gt38.0 ?C)
• Tender Adenopathy
• Adenopathy
• Data extraction from 2x2 tables
• Analysis with likelihood ratios, ROC-curves,
  probability nomogram
• I²-index for heterogeneity
• Where heterogeneity is acceptable, likelihood
  ratios can be pooled

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Methods (4) data extraction and analysis of
validation of the Centor score

• Predicted versus observed
• Forest plots using Random effect model
• I²-index for heterogeneity
• Prevalence correction

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Results (1)

• 340 potentially relevant articles
• 16 studies included- 16 studies signs and
  symptoms 3371 patients
• - 11 studies validation of the Centor score
  1603 patients
• Large variability in prevalence 4.7 - 36.8

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Positive likelihood ratios
Sign of any exudates
Pooled Positive LR 1.95 (1.63 2.32) I²
74.2 (heterogeneity)
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Negative likelihood ratios
Sign of Absence of cough
Pooled Negative LR 0.59 (0.50 0.69) I²
22.7 (heterogeneity)
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Results (2) Diagnostic accuracy of signs and
symptoms

• Very heterogeneous results
• No powerful likelihood ratios
• Conclusion no sign or symptom on its own is
  powerful enough to rule in or rule out the
  diagnosis of streptococcal pharyngitis

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Results (3) Validation of the Centor score

• The Centor score
• four items 1. Tonsillar exudate
• 2. Tender cervical anterior adenopathy
• 3. History of fever (or gt38.0?C)
• 4. Absence of cough
• Each item gets 1 point. Score 0-4 points

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Forest plot for Centor score 0-1
I² 5 of heterogeneity Z 2.77, P 0.006
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Forest plot for Centor score 2-3
I² 62 of heterogeneity Z 1.15, P 0.25
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Forest plot for Centor score 4
I² 7 of heterogeneity Z 1.33, P 0.18
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Prevalence correction
Adjusted for pooled prevalence of 21.9
Centor Score 1
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Results (4) Validation of the Centor score

• Conclusions
• Heterogeneity is acceptable
• Underprediction for Centor score 0-1
• No significant difference between predicted and
  observed values in Centor score 2-4
• Underprediction in studies with a higher
  prevalence and overprediction in studies with a
  lower prevalence, compared with Centors
  prevalence
• Correction with a pooled prevalence is possible