Scoring System for Streptococcal Pharyngitis
Use the Centor criteria (or modified McIsaac score) to determine which patients need laboratory testing, but never treat based on clinical score alone—always confirm with rapid antigen detection test (RADT) or throat culture before prescribing antibiotics. 1, 2
The Centor/McIsaac Clinical Scoring System
The scoring system assigns points based on these clinical features:
- Fever >38°C (100.4°F): 1 point 1, 3
- Absence of cough: 1 point 1
- Tender anterior cervical lymphadenopathy: 1 point 1
- Tonsillar swelling or exudate: 1 point 1
- Age modification (McIsaac): Age 3-14 years adds 1 point; age 15-44 years adds 0 points; age ≥45 years subtracts 1 point 3
How to Use the Score Algorithmically
Score 0-1: Do NOT test
- These patients have very low probability of Group A Streptococcus (GAS) and should not undergo testing 1
- Treat symptomatically with analgesics only 1
Score 2-3: Perform RADT or throat culture
- In children and adolescents: Perform RADT; if negative, back up with throat culture because RADT sensitivity is <90% in pediatrics 1
- In adults: Perform RADT; negative results do NOT require backup culture due to low disease prevalence (5-15%) and minimal rheumatic fever risk 1
Score 4: Perform RADT or consider empiric treatment
- High probability of GAS infection, but laboratory confirmation is still recommended before treatment 1
- Even patients with all clinical features have confirmed streptococcal pharyngitis only 35-50% of the time 1
Critical Age-Specific Considerations
Children under 3 years should NOT be tested routinely because GAS pharyngitis is uncommon in this age group, acute rheumatic fever is exceptionally rare, and the classic presentation is atypical. 4, 5 Testing may be considered only when an older sibling or household contact has documented GAS infection. 4
Peak age for testing is 5-15 years, when GAS causes 15-30% of acute pharyngitis cases. 1, 5, 3
Adults have lower disease prevalence (5-15% of pharyngitis), making the threshold for testing appropriately higher. 1
Treatment Algorithm After Positive Test
First-line therapy:
- Penicillin V: 250 mg twice or three times daily for 10 days 1, 6
- Amoxicillin: Alternative penicillin option for 10 days 7
For penicillin allergy (non-anaphylactic):
For penicillin allergy (anaphylactic-type):
- Clindamycin, clarithromycin, or azithromycin 7, 8
- Note: Macrolide resistance exists in some geographic regions 9
Common Pitfalls to Avoid
The most critical error is overtesting and overtreating. Over 60% of adults with sore throat receive antibiotics, yet only 20-30% of pediatric pharyngitis and 5-15% of adult pharyngitis is actually due to GAS. 1, 2 This leads to:
- Identification of asymptomatic carriers (20% of school children carry GAS asymptomatically) rather than true infections 1
- Unnecessary antibiotic prescriptions contributing to antimicrobial resistance 1, 2
- Increased costs and medicalization 1
Never diagnose or treat based on clinical features alone, even with high scores—the clinical overlap between viral and bacterial pharyngitis is too broad for accurate diagnosis without laboratory confirmation. 1, 2
Recognize viral features that make testing unnecessary: cough, rhinorrhea, hoarseness, conjunctivitis, and diarrhea strongly suggest viral etiology regardless of other symptoms. 4, 2
Benefits of Appropriate Antibiotic Treatment
When GAS is confirmed, antibiotics provide modest symptom relief (shortening duration by 1-2 days, with number needed to treat of 6 at day 3 and 21 at week 1). 1 More importantly, treatment prevents:
- Acute rheumatic fever (particularly important in children 5-15 years) 1, 7
- Suppurative complications like peritonsillar abscess 1, 7
- Disease transmission to close contacts 1, 7
Treatment within 9 days of symptom onset still prevents acute rheumatic fever, so there is no need to rush treatment before laboratory confirmation. 2