Distinguishing Features of GAS and Viral Pharyngitis
The most reliable way to differentiate between Group A Streptococcal (GAS) pharyngitis and viral pharyngitis is through laboratory testing, as clinical features alone do not reliably discriminate between the two conditions except when overt viral features like rhinorrhea, cough, oral ulcers, and hoarseness are present. 1
Key Clinical Features
GAS Pharyngitis Features:
- Sudden onset of sore throat
- Pain on swallowing
- Fever
- Headache
- Nausea, vomiting, and abdominal pain (especially in children)
- Tonsillopharyngeal inflammation
- Patchy tonsillopharyngeal exudates
- Palatal petechiae
- Anterior cervical adenitis (tender nodes)
- Typically occurs in winter or early spring
- History of exposure to streptococcal pharyngitis
- Scarlatiniform rash may be present
- Most common in children 5-15 years of age 1
Viral Pharyngitis Features:
- Conjunctivitis
- Coryza (nasal discharge)
- Cough
- Diarrhea
- Hoarseness
- Discrete ulcerative stomatitis
- Viral exanthem (rash)
- Rhinorrhea 1, 2
Diagnostic Approach
The Infectious Diseases Society of America (IDSA) emphasizes that clinical features alone cannot reliably differentiate between GAS and viral pharyngitis 1. Even experienced clinicians cannot make this diagnosis with certainty based solely on clinical grounds 2.
When to Test:
- Test patients with sore throat without overt viral features
- Testing is not recommended when clinical features strongly suggest viral etiology (cough, rhinorrhea, hoarseness, oral ulcers) 1, 2
- Testing is generally not indicated for children <3 years old due to the rarity of acute rheumatic fever in this age group 1
Diagnostic Methods:
Rapid antigen detection test (RADT)
- A positive RADT is diagnostic for GAS pharyngitis
- Highly specific but variable sensitivity
Throat culture
- Gold standard for diagnosis
- In children and adolescents, negative RADT should be backed up with throat culture
- Backup culture is not routinely necessary for adults due to low incidence of GAS pharyngitis and exceptionally low risk of acute rheumatic fever 1
Clinical Pitfalls to Avoid
Relying solely on clinical features: The signs and symptoms of GAS and viral pharyngitis have substantial overlap, making clinical diagnosis unreliable 1, 3.
Treating without testing: Except when overt viral features are present, laboratory confirmation is necessary before initiating antibiotic therapy 1, 4.
Overtesting: Testing is not recommended for patients with clear viral symptoms or children under 3 years without specific risk factors 1.
Misinterpreting carriers vs. acute infection: Some patients may be GAS carriers experiencing viral pharyngitis. Consider this possibility in recurrent or persistent cases 1.
Ignoring non-GAS streptococcal pharyngitis: Groups C and G streptococci can also cause pharyngitis, particularly in college students and adults 1.
Treatment Considerations
- Penicillin or amoxicillin is the treatment of choice for confirmed GAS pharyngitis 1, 4
- For penicillin-allergic patients, first-generation cephalosporins (if not anaphylactically sensitive), clindamycin, clarithromycin, or azithromycin are alternatives 1, 5
- Antibiotics should not be used for viral pharyngitis 2
By following these guidelines and understanding the distinguishing features, clinicians can more accurately diagnose and appropriately treat pharyngitis, reducing unnecessary antibiotic use while ensuring proper management of GAS infections.