How do I differentiate and treat bacterial vs viral pharyngitis (inflammation of the pharynx) in a patient, considering factors such as fever, tonsillar exudates, and cervical lymphadenopathy, and a potential history of penicillin allergy?

Differentiating and Treating Bacterial vs Viral Pharyngitis

Use the modified Centor criteria to stratify patients, perform rapid antigen detection testing (RADT) for Group A Streptococcus (GAS) in those with ≥2 criteria, and treat confirmed GAS pharyngitis with penicillin or amoxicillin for 10 days (or azithromycin for 5 days in penicillin-allergic patients). 1

Clinical Differentiation: Viral vs Bacterial Features

Features Strongly Suggesting Viral Etiology (Do NOT Test or Treat)

• Cough, rhinorrhea (runny nose), conjunctivitis, hoarseness, or diarrhea strongly indicate viral pharyngitis and testing for GAS is not recommended 1
• Oropharyngeal ulcers or vesicles suggest viral infection 1
• Most pharyngitis cases (70-85% in adults, 65-85% in children) are viral, caused by rhinovirus, coronavirus, adenovirus, influenza, Epstein-Barr virus, or other viruses 1

Features Suggesting Bacterial (GAS) Pharyngitis

• Sudden onset of sore throat 1, 2
• Fever (temperature >100.4°F/38°C) 1, 3
• Tonsillar exudates (white patches on tonsils) 1, 3
• Tender anterior cervical lymphadenopathy (swollen, painful neck lymph nodes) 1, 3
• Absence of cough 1
• Additional supportive findings: scarlatiniform rash, palatal petechiae, swollen tonsils, headache, nausea/vomiting 1, 2
• Peak age 5-15 years; presentation in winter/early spring 1, 2

Diagnostic Algorithm Using Modified Centor Criteria

The modified Centor criteria assign 1 point each for: 1, 4

1. History of fever
2. Tonsillar exudates
3. Tender anterior cervical adenopathy
4. Absence of cough

Testing Strategy Based on Score:

• 0-1 criteria: Do NOT test or treat - likelihood of GAS is <10%, viral etiology most likely 1, 4

• 2-3 criteria: Perform RADT - treat only if positive 1, 4

  • If RADT is negative in children and adolescents, confirm with throat culture due to higher risk of rheumatic fever 1
  • If RADT is negative in adults, backup culture is NOT routinely needed due to low rheumatic fever risk and lower GAS prevalence 1

• 4 criteria: Either perform RADT or treat empirically - GAS probability is 40-60% 4

Critical caveat: Clinical features alone cannot definitively diagnose GAS pharyngitis even in experienced hands; microbiological confirmation is essential to avoid unnecessary antibiotic use 1

Special Considerations: Infectious Mononucleosis

• Suspect EBV (infectious mononucleosis) when: generalized lymphadenopathy (not just anterior cervical), significant fatigue, posterior cervical adenopathy, splenomegaly, and absence of cough/rhinorrhea 5
• The sore throat of mononucleosis mimics streptococcal pharyngitis but typically lacks the classic exudates pattern 5
• NEVER prescribe amoxicillin or ampicillin if EBV is suspected - causes severe maculopapular rash in 80-90% of cases 6
• Patients may be GAS carriers experiencing concurrent viral mononucleosis; if both EBV and GAS are confirmed, treat the streptococcal infection appropriately 5

Red Flags Requiring Urgent Evaluation

Immediately evaluate for serious complications if patient has: 1

• Difficulty swallowing or drooling
• Neck tenderness or swelling
• Unilateral tonsillar swelling (consider peritonsillar abscess)
• Severe symptoms in adolescents/young adults (consider Fusobacterium necrophorum and Lemierre syndrome)

Treatment Recommendations

For Confirmed GAS Pharyngitis (Positive RADT or Culture):

First-line therapy (non-penicillin allergic): 1, 7

• Penicillin V 250-500 mg orally 2-3 times daily for 10 days 1, 7
• OR Amoxicillin 500 mg twice daily for 10 days (equally effective, more palatable) 1, 3
• These are preferred due to narrow spectrum, low cost, and no reported GAS resistance 1

For penicillin-allergic patients (non-anaphylactic): 1

• First-generation cephalosporin for 10 days 1

For penicillin-allergic patients (anaphylactic or severe allergy): 1, 8

• Azithromycin 12 mg/kg once daily for 5 days (pediatrics) or standard adult dosing 1, 8
• OR Clindamycin for 10 days 1
• OR Clarithromycin for 10 days 1
• Note: Approximately 1% of GAS isolates develop azithromycin resistance post-therapy 8

For Viral Pharyngitis (Negative Testing or <2 Centor Criteria):

Supportive care only - NO antibiotics: 1

• Acetaminophen or NSAIDs (ibuprofen) for pain and fever control 1
• Avoid aspirin in children due to Reye syndrome risk 1
• Warm saline gargles, adequate hydration 6
• Symptoms typically resolve in 3-7 days without treatment 1

Common Pitfalls to Avoid

• Do not prescribe antibiotics based on clinical impression alone without microbiological confirmation - this leads to massive antibiotic overuse 1, 9
• Do not test children <3 years old unless high-risk factors present (e.g., older sibling with GAS) - GAS pharyngitis and rheumatic fever are rare in this age group 1
• Do not perform follow-up cultures after treatment unless special circumstances exist 1
• Do not test or treat asymptomatic household contacts 1
• Recognize chronic GAS carriers (positive tests despite appropriate treatment) who are experiencing recurrent viral infections - these patients are at low risk for complications and generally do not need treatment 1, 3
• Corticosteroids are NOT recommended as adjunctive therapy 1