In a young adult with sore throat, fever and exudative tonsillitis, how should I differentiate viral from group A beta‑hemolytic streptococcal infection and what is the appropriate work‑up and management?

Differentiating Viral from Bacterial Pharyngitis in Young Adults with Exudative Tonsillitis

Clinical features alone cannot reliably distinguish viral from Group A streptococcal pharyngitis, even by experienced physicians, and microbiological confirmation with rapid antigen detection testing (RADT) or throat culture is mandatory before prescribing antibiotics. 1

Clinical Assessment: Features Suggesting Bacterial vs. Viral Etiology

Features Favoring Group A Streptococcus (GAS)

• Sudden onset of sore throat with high fever (>101°F/38.3°C) 1
• Severe dysphagia (pain on swallowing) 2
• Tonsillopharyngeal erythema with patchy discrete exudate 1
• Tender, enlarged anterior cervical lymph nodes 1
• Palatal petechiae 3
• Absence of viral upper respiratory symptoms (no cough, rhinorrhea, hoarseness, conjunctivitis) 1, 3
• Headache, nausea, vomiting, or abdominal pain 1

Features Strongly Suggesting Viral Etiology

• Presence of cough, rhinorrhea (coryza), hoarseness, or conjunctivitis 1, 3
• Discrete oral ulcers or ulcerative stomatitis 3
• Diarrhea 1
• Gradual onset of symptoms 3

Critical caveat: GAS causes only 5-10% of acute pharyngitis cases in adults (compared to 15-30% in children aged 5-15 years), making viral etiologies far more common in young adults. 1

Diagnostic Algorithm

Step 1: Initial Clinical Screening

• If obvious viral features are present (cough, rhinorrhea, conjunctivitis, oral ulcers), do not perform GAS testing and manage supportively. 3
• If viral features are absent and bacterial features are present (fever, exudate, tender anterior cervical nodes, absence of cough), proceed to microbiological testing. 3

Step 2: Microbiological Confirmation

• Perform RADT as the initial test for suspected GAS pharyngitis. 3
• A positive RADT is diagnostic and warrants immediate antibiotic therapy. 3
• In young adults, a negative RADT does not require backup throat culture due to the low risk of rheumatic fever in this population and the generally high specificity (90-96%) of RADT. 1, 3
• Throat culture on sheep blood agar remains the gold standard with 90-95% sensitivity but requires 24-48 hours for results. 1

Important pitfall: Clinical scoring systems (Centor, McIsaac) help identify low-risk patients who don't need testing, but they cannot definitively diagnose GAS pharyngitis—microbiological confirmation is still required for treatment decisions. 1

Management Based on Test Results

Confirmed GAS Pharyngitis (Positive RADT or Culture)

• First-line therapy: Penicillin V or amoxicillin for 10 days due to proven efficacy, narrow spectrum, safety, low cost, and zero resistance. 3
• For non-anaphylactic penicillin allergy: narrow-spectrum cephalosporin (cefadroxil or cephalexin) for 10 days. 3
• For true penicillin allergy/anaphylaxis: clindamycin (≈1% GAS resistance) or macrolide (5-8% resistance, use with caution). 3
• Complete the full 10-day course to ensure bacterial eradication and prevent rheumatic fever. 3

Viral Pharyngitis (Negative Testing or Obvious Viral Features)

• Do not prescribe antibiotics. 3
• Supportive care only: analgesics (acetaminophen or NSAIDs), adequate hydration, warm saline gargles, topical anesthetics, and rest. 3

Special Considerations in Young Adults

Infectious Mononucleosis (EBV)

• Suspect when exudative pharyngitis is accompanied by generalized lymphadenopathy (especially posterior cervical), splenomegaly, and prolonged fatigue. 1, 4
• Never prescribe amoxicillin or ampicillin if EBV is suspected—these cause a severe maculopapular rash in 80-100% of infectious mononucleosis cases. 4
• Confirm with heterophile antibody test (monospot) or EBV-specific serology. 4, 5

Other Bacterial Causes (Uncommon)

• Groups C and G streptococci can cause exudative pharyngitis but are far less common than GAS. 1, 6
• Arcanobacterium haemolyticum may cause pharyngitis with scarlatiniform rash in adolescents/young adults. 3
• Mycoplasma pneumoniae and Chlamydia pneumoniae are uncommon pharyngitis causes. 1

Common Pitfalls to Avoid

• Do not treat based on clinical impression alone—this leads to unnecessary antibiotic use in 50-70% of cases, as viral causes predominate. 1
• Do not assume all exudative pharyngitis is bacterial—viruses (especially adenovirus, EBV) frequently cause exudative tonsillitis. 1, 7
• Do not test or treat asymptomatic household contacts. 1
• Do not perform routine post-treatment testing unless symptoms persist or recur. 1
• Recognize that a positive test may represent asymptomatic GAS carriage (10-15% of population) with concurrent viral pharyngitis, especially if clinical features are atypical. 1, 3